Are wasps attracted to UV light emissions?

Are wasps attracted to UV light emissions?

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I remember seeing a documentary where it was shown that bees and wasps are attracted to UV components of a flower colour (please correct me if I am wrong).

Does this mean that they could be attracted by neon lights (that I suspect are emitting also in the UV part of the spectrum)?

I am asking because I have neon lights in my office and if I have the lights on I can't open the window, or a wasp will almost immediately enter the office. I've experimented a bit, and turning off the light makes the wasp go out rather quickly, hence my hypothesis.

I am located in Europe, if that makes a difference for the species involved. Outside the window we have some tall trees, so we keep some lights on even when the sun is out.

Tuning the white light spectrum of light emitting diode lamps to reduce attraction of nocturnal arthropods

Artificial lighting allows humans to be active at night, but has many unintended consequences, including interference with ecological processes, disruption of circadian rhythms and increased exposure to insect vectors of diseases. Although ultraviolet and blue light are usually most attractive to arthropods, degree of attraction varies among orders. With a focus on future indoor lighting applications, we manipulated the spectrum of white lamps to investigate the influence of spectral composition on number of arthropods attracted. We compared numbers of arthropods captured at three customizable light-emitting diode (LED) lamps (3510, 2704 and 2728 K), two commercial LED lamps (2700 K), two commercial compact fluorescent lamps (CFLs 2700 K) and a control. We configured the three custom LEDs to minimize invertebrate attraction based on published attraction curves for honeybees and moths. Lamps were placed with pan traps at an urban and two rural study sites in Los Angeles, California. For all invertebrate orders combined, our custom LED configurations were less attractive than the commercial LED lamps or CFLs of similar colour temperatures. Thus, adjusting spectral composition of white light to minimize attracting nocturnal arthropods is feasible not all lights with the same colour temperature are equally attractive to arthropods.

1. Introduction

Artificial night lighting is a major convenience in modern society, because an illuminated realm during the night provides more time for humans to safely stay active. Despite its practical application, contemporary night lighting poses risks to human and ecological health [1,2]. Circadian rhythms are biological cycles that run on a daily cycle and can be easily disrupted with exposure to certain wavelengths of light at night [3–5]. Night-time illumination allows humans to be more active at night, while simultaneously drawing vectors closer to humans [6]. Arthropods in particular are strongly affected by light at night, and numbers of phototactic species increase near the light sources throughout the night [7–10], which provides the basis for light traps used widely in entomology [11]. Attraction of insects to artificial lighting is also implicated in alterations in insect species distributions [12] and is a suspected but largely uninvestigated factor in declines of nocturnal species [13].

Spectral composition of light influences degree of positive phototaxis for insects [14–17]. Differences in wavelength, colour saturation and brightness of light are the most important characteristics that influence insect attraction to lights [18]. Similarities in positive phototaxis exist within orders [19]: for instance, mosquitoes and midges (Diptera) are attracted to ultraviolet (UV), blue and green light [20–23]. House flies (Glossina morsitans morsitans and Musca domestica Diptera) show slight variation, exhibiting positive phototaxis to green and red lights in addition to UV [24]. Lepidoptera are strongly attracted to UV and blue [25–29], with a peak around 400 nm [3]. Kissing bugs (Hemiptera) are attracted to blue light and are guided by low intensity white lights [30], whereas honeybees (Hymenoptera) have positive phototaxis peaks in the UV and blue range of light [31].

The current trend in lighting technology is to replace older lamp types with energy-efficient light-emitting diode (LED) lamps for both indoor and outdoor lighting. The earliest LED lamps meant for area lighting consisted of a blue LED that was coated with a phosphor to create a full-spectrum white light that had very high emissions in the blue portion of the spectrum (i.e. a high colour temperature >5000 K high colour temperatures appear ‘cold’, whereas low colour temperatures appear ‘warm’). Subsequent developments have led to LEDs with a range of colour temperatures for outdoor and indoor use (2700–5000 K), but all of these lamp types have more blue light emissions to which flying insects are generally attracted than do some older technologies (e.g. high-pressure sodium and low-pressure sodium lamps) [32]. Experimental investigations into insect attraction to LEDs have been mixed, with one study showing lower attraction of insects to LEDs of a range of colour temperatures than to high-pressure sodium and other lamp types [9] and another study showing greater attraction to a 4000 K LEDs than to high-pressure sodium lamps and no significant differences in attraction of insects to LEDs of different colour temperatures [33]. Furthermore, because of the full-spectrum nature of high-efficiency outdoor lights like LEDs, scientists have warned against increasing ecological effects resulting from greater blue light emissions, pointing to the effects on bats [34], insects [33], circadian rhythms across species [35,36] and ecological interactions [37–39].

Despite concern about the effects of the spectral composition of night lighting on wildlife posed by newer lighting technologies, few tools are available to predict attractiveness of any given source of light to insects. Most studies test representatives of different insect orders against specific wavelengths of light scattered across the spectrum or compare attraction for off-the-shelf lamps of various types and colour temperatures [7,9,15,33]. According to van Grunsven et al. [14], only two studies contain continuous attraction spectra that provide relative attractiveness of each wavelength for an insect group (i.e. [40] for moths and [31] for honeybees). With these curves, the attractiveness of any given light source can be calculated by multiplying the relative output of a given lamp at each wavelength by the reaction strength given for that wavelength in the model and then summing the resulting products [14]. In their recent work, van Grunsven et al. [14] found that these attractiveness curves did not perform well when lamps with high UV emissions (i.e. those measured to be highly attractive in both models) were not included in the evaluation.

In this study, we concentrate on indoor lighting that must be full spectrum to allow colour rendering. We take advantage of LEDs that create a full-spectrum light through use of multiple colours of diodes (red, blue, green RBG) in conjunction with white diodes such that they can be adjusted in ways intended to minimize insect attraction. We use indices based on existing insect attraction curves to develop custom LED configurations and compare them with commercial LEDs and compact fluorescent bulbs of similar colour temperatures intended for indoor use. The results should also apply outdoors where full spectrum light is needed and LED technologies allow tuning of the spectrum. We note at the outset, however, that outdoor installations usually do not require full-spectrum lighting, and even lower colour temperatures and filters to avoid sensitive wavelengths would be environmentally preferable [36,41].

2. Material and methods

(a) Experimental design

We captured arthropods in light traps at night between 17 February 2014 and 14 May 2014 at three sites in Los Angeles County, California (figure 1). An urban site was located in the UCLA Mildred E. Mathias Botanical Garden (34.066°N 118.441°W, Los Angeles, Los Angeles County). Two rural sites were UCLA La Kretz Center Field Station (34.097°N, 118.816°W, Malibu, Los Angeles County) and UCLA Stunt Ranch Santa Monica Mountains Reserve (34.093°N, 118.657°W, Calabasas, Los Angeles County). We erected six traps on each site each night, with a minimum of 11 m between traps. Each trap contained a separate light source—three tuneable LED lights consisting of RGB and W diodes produced by Philips Research Laboratories in Eindhoven, The Netherlands, one of two commercial LEDs with only W diodes, one of two commercial compact fluorescent lamps (CFLs), and an empty light housing as a ‘no light’ control (table 1).

Table 1. Characteristics of lamps used for light traps. A, B and C are customizable LEDs. LED1 and LED2 are two commercial LEDs, and CFL1 and CFL2 are compact fluorescent lamps. Predicted attractiveness to moths [40] and honeybees [31] is listed (see §2c).

Figure 1. Site locations of insect traps and their placement at each field site for collecting in March–May 2014 in Los Angeles County, California. Two sites (La Kretz and Stunt Ranch) are in rural environments and the third (Mildred E. Mathias Botanical Garden) is in an urban environment. (Online version in colour.)

Light traps were PVC pipe tripods from which light sources were suspended above a collection receptacle (figure 2). The lights were fully shielded and directed downward at the pan trap. We constructed the pan trap from the bottom of a white plastic bucket (26 × 7 cm) that we suspended with 2-mm thick wire 10 cm below the light source and filled with soapy water to trap flying arthropods. The non-lighted control trap was an identical collection tray with the same housing but no lamp (figure 2).

Figure 2. Schematic of light trap design, showing total height (2.5 m), collection dish height (1.8 m), distance of light source to collection dish (10 cm), height of collection dish (7 cm), diameter of collection dish (26 cm) and minimum distance between two light traps (11 m). Traps were deployed March–May 2014 in Los Angeles County, California. (Online version in colour.)

After 19 collections, we confirmed with measurements that our commercial LED lamps and CFLs were not producing the illumination specified and we replaced those two bulbs with models with greater output. Illumination produced by each lamp was measured at surface of the pan trap and at 2 m horizontally from the trap with an ExTech light meter (model no. 401027). Light from each of the lamps was directed downward at the pan trap in the same manner.

We collected samples during 32 nights: 16 at the urban site and eight each at the two rural sites. At least one night was skipped between consecutive collections at a field site to minimize any effects from the previous collection and to avoid depleting the number of arthropods.

On each night of collecting, we recorded temperature, humidity and wind speed at the beginning and end of each period of collection. Additionally, we recorded moon phase and position of traps within each site to account for potential environmental effects that could affect the number of arthropods collected in each light. We recorded ambient temperature (±0.1°C) with a digital thermometer and wind speed (±0.1 m s −1 ) with a handheld anemometer.

We turned lights on at sunset and off at sunrise to collect during this period sunset times varied from 17 : 39 to 19 : 47 and sunrise times varied from 06 : 13 to 07 : 06 during the study. We rotated the location of traps each treatment clockwise at each site on successive collection nights to provide at least one night at each position. All specimens collected were immediately removed from traps after one elapsed night of collecting and taken to the laboratory for sorting.

(b) Sorting procedures

We rinsed each sample through a 255 µm mesh and preserved contents in 95% ethanol. We then transferred specimens to a Petri dish filled with 95% ethanol and observed them under a dissecting microscope. We sorted to taxonomic order with guidance from reference figures and descriptions [42,43]. Each order from each night of collecting was then prepared separately and deposited at the Natural History Museum of Los Angeles County.

(c) Light spectrum selection

Lamps with lower colour temperatures are known to attract fewer insects [8,9], so we used two LED lamp configurations that had a colour temperature of approximately 2700 K (2704 and 2728 K) and controls that had a 2700 K colour temperature. For comparison, we included one custom LED configuration with a colour temperature of 3510 K.

The three customizable LED lamps could be tuned to one of six configurations, each with emissions curves provided by the manufacturer. Modifying slightly the approach of van Grunsven et al. [14], we calculated relative attractiveness of each configuration by multiplying percentage total output at each wavelength by percentage total attractiveness for each wavelength for moths [40] and honeybees [31]. In this manner, a lamp that followed each response curve exactly would have an attractiveness of unity, whereas one that avoided those wavelengths entirely would have an attractiveness of zero. Both the insect attraction curves [31,40] were obtained in digital form from the International Commission on Illumination. We then chose the configurations of the lamps that minimized attractiveness for both curves at 3510 K colour temperature (one lamp, designated A), and at approximately 2700 K colour temperature (two lamps, B and C).

For the commercial CFLs and LEDs (both 2700 K), we used a USB650 red tide spectrometer (Ocean Optics) to measure the spectral profile and then calculated the attractiveness index for each emission spectrum.

(d) Statistical methods

We used a generalized linear model (GLM) with a Poisson distribution and log link function to analyse number of arthropods captured. We tested for and adjusted for overdispersion of the counts by estimating the overdispersion factor and adjusting the likelihood functions and confidence intervals accordingly in JMP P ro v. 11.2 (SAS Inc., Cary, NC). Environmental variables, location, pan illumination and lamp type were used to predict the number of specimens trapped for each order that contained a sufficient sample size the remaining orders were pooled together. Illumination measured horizontally from the trap correlated highly with vertical illumination at the pan (Pearson's r = 0.97) and is not included in any models. We standardized environmental variables by their mean and range, so that all parameters ranged from zero to unity and thus their coefficients in the model could be compared. We evaluated alternative models with Akaike's information criterion scores corrected for sample size (AICc) [44].

We also performed, with a Bayesian probabilistic model, pairwise comparisons of the effect of lamp type on number of arthropods captured. A Bayesian approach reduces the risk of falsely finding a significant difference when making multiple pairwise comparisons. We computed the posterior probability distribution of the effect of lamp type conditioned to the data observed via Markov chain Monte Carlo simulations with JAGS v. 3.3.0 and R v. 3.0.1 software programs. We extracted samples from five chains, and a 5000 iteration burn-in period was used to dilute the influence of initial values in the results. Samples were thinned at five steps to reduce the time correlation between them. The correlation between successive samples was inspected with autocorrelation plots. We standardized environmental variables by their mean and standard deviation to improve the mixing properties of the chain. We also transformed the predicted variable by adding 1 to each value of captured arthropods to avoid taking the log of zero in the model.

We also calculated at the correlation (Pearson's r) between the GLM coefficients for each lamp type and the attractiveness values calculated for the lamps and did the same for the Bayesian model coefficients.

The dataset supporting this article is provided as the electronic supplementary material.

3. Results

(a) Characterization of lamps

The spectral output of the 2700 K tuneable LEDs (B and C) differed substantially from that of the commercial LEDs (figure 3). The tuneable 2700 K LEDs are characterized by peaks of emission at 450 and 525 nm with the greatest output at 675 nm, whereas the commercial LEDs had a higher output across the shorter wavelengths. The 3500 K LED had emission peaks similar to the 2700 K lamps, but also had greater output at all wavelengths between those peaks. The two commercial LEDs and two CFLs used as controls were so similar in output that they were considered to be the same treatment for the remainder of the calculations (figure 3). Lamps B and C were very similar except that C had slightly more emissions in the red portion of the spectrum.

Figure 3. Insect attraction and lamp output curves by wavelength. Top: response curves for moths (Cleve) [40] and honeybees (Menzel) [31]. Middle: output from 3500 K custom LED (A), 2700 K custom LEDs (B,C, with differences so minor they are not visible at this scale) and commercial 2700 K LEDs (LED representing two lamps with minor differences). Bottom: output from commercial 2700 K compact fluorescent lamp (CFL representing two lamps with minor differences). (Online version in colour.)

(b) Insect collections

We collected 5579 arthropods over 32 nights. Mean numbers of arthropods varied greatly by order and lamp type (figure 4). Diptera made up 67.5% of the specimens, Lepidoptera accounted for 12.0% and all remaining orders for the remaining 20% with Collembola (7.5%) and Hymenoptera (4.4%) making the greatest proportion.

Figure 4. Mean of the number of specimens caught per night for all specimens, Diptera, Lepidoptera and other orders combined for each lamp type (n = 32 nights) for collections March–May 2014 in Los Angeles County, California. 95% confidence intervals calculated from generalized linear model for each grouping (see §2d). A, 3510 K custom LED B, 2704 K custom LED C, 2728 K custom LED CFL, 2700 K compact fluorescent lamps LED, commercial 2700 K LEDs NO, control. (Online version in colour.)

(c) Environmental conditions

Overnight temperature ranged from 9.65°C to 23.25°C, humidity ranged from 19 to 89%, and winds ranged from calm to 1.6 m s −1 . Temperature, wind speed and humidity were correlated, but did not exceed an absolute value of 0.55 and so were included in the multivariate analyses. Percentage moon visible ranged from 9.9 to 99.8, but we did not include it in the models because it correlated with weather variables such that results would be spurious: the high degree of light pollution in Los Angeles County would certainly confound levels of light from different moon phases, especially under cloud cover [45], and the time of moonrise may or may not occur during periods of peak invertebrate flights.

(d) Generalized linear models

With a GLM, we compared all lamp types to investigate the effect on number of total specimens, Diptera, Lepidoptera and other orders combined. Candidate models included mean temperature, relative humidity, maximum wind speed, lamp type, lamp placement in the field and illumination from the lamp as explanatory variables.

The best models (lowest AICc) for each group only included lamp type (table 2). For the Lepidoptera, the coefficient for the 2700 K CFL was greatest, followed by the commercial LED, the 3500 K LED, then the two 2700 K LEDs (table 3). For the Diptera and other orders model, the 3500 K LED was more attractive than the commercial LED, but CFL was most attractive and the tuneable 2700 K LEDs were least attractive.

Table 2. Generalized linear models assessing contribution of lamp type, illumination, location and environmental conditions on number of Diptera, Lepidoptera, and other orders of invertebrates captured per night at two rural (n = 8 each) and one urban (n = 16) site in Los Angeles County, California, March–May, 2014.

Table 3. Coefficients for best generalized linear model explaining attraction of all specimens, Diptera, Lepidoptera, and other orders (mean 95% confidence interval and chi-squared p-values). Data collected over 32 total nights at two rural and one urban site in Los Angeles County, California, March–May 2014.

(e) Bayesian comparisons of attractiveness

Using a Bayesian log linear Poisson model, we assessed statistical significance of the difference in effects caused by lamp type on number of arthropods captured. Variables included in the model were mean temperature, mean relative humidity, lamp type, lamp placement in the field and maximum wind speed. From this statistical model, we computed a set of posterior probability distributions of the random variables representing the effect difference of two types of lamps on the number of arthropods captured. A positive value for this difference indicates that the trap illuminated by the first lamp is expected to capture more arthropods than the trap with the second lamp. The reverse is valid if the difference is negative. The difference is considered statistically significant if the 95% highest density interval (HDI) of its posterior distribution data does not contain the value zero. The mean and 95% HDI for a set of pairwise comparisons between lamp types (table 4) notably shows that the custom LEDs attracted significantly fewer insects than a commercial LED of the same colour temperature.

Table 4. Difference of effect of different lamp types on the number of invertebrates captured in traps. Data collected over 32 total nights split among two rural (eight nights each) and one urban site (16 nights) in Los Angeles County, California, March–May 2014.

(f) Performance of attractiveness indices

The modelled attractiveness index for bees correlated significantly with the GLM model coefficients for Lepidoptera (r = 0.99 p = 0.0003). The modelled attractiveness index for moths correlated with GLM coefficients for Diptera (r = 0.89, p = 0.04), Lepidoptera (r = 0.91 p = 0.02). When data from the CFL were excluded (as suggested by van Grunsven et al. [14]), the modelled bee attractiveness index correlated poorly with Diptera attraction (n.s.), but extremely well with Lepidoptera attraction (r = 0.98 p = 0.015), and weakly with attraction for other orders (n.s.). Similar results were found for correlations with coefficients from the Bayesian analysis.

4. Discussion

All lamp types attracted more arthropods than the no-light control thus, it is likely that in this regard, reducing arthropods attracted to light with currently available technology will always be a matter of mitigating the effects, which is true for many of the adverse effects of artificial night lighting [1,46,47]. Inasmuch as all light attracts arthropods, our finding that LEDs generally attract substantially fewer moths and other arthropods than a CFL with the same colour temperature is consistent with previous research [9,14,15,26,27]. It contradicts the broad claim by Pawson & Bader [33] that LEDs always worsen ecological light pollution, which was derived from comparisons of 4000 K LEDs to high-pressure sodium vapour lights (which have a lower colour temperature). Colour temperature mattered in our results, again differing from Pawson & Bader [33], with our 3500 K tuneable LED generally being more attractive to arthropod groups than the commercial 2700 K LEDs. The 3500 K LED, however, was as attractive to Diptera as the 2700 K CFL. The difference in the response of Diptera may reflect a different response spectrum for flies compared with moths and other insects flies exhibit attraction to green and red light as well as to shorter wavelengths [24] and the 3500 K LED had emissions spread through the green and into the red.

We found that our two tuneable 2700 K LEDs were 20% and 21% less attractive to all orders combined than the commercial 2700 K LED in the Bayesian models. Because of slight differences in the housings for the lamps, the amount of light delivered on the pan traps was higher for the custom LEDs than for the commercial LED, so this result does suggest that spectrum was the dominant variable in the differences observed—a more intense custom spectrum was less attractive to arthropods than the corresponding commercially available spectrum at the same colour temperature. Notwithstanding recent results [33], previous research has shown lower colour temperature LEDs attract fewer arthropods than higher colour temperatures [9]. Our results show for the first time, to the best of our knowledge, that even at the same colour temperature, adjustment of spectral composition can influence insect attraction. For example, the two 2700 K custom LEDs attracted around three times fewer Hemiptera than the commercial 2700 K LEDs (table 4).

It may surprise some that illumination was not found to be important in predicting the attraction of invertebrates to the different light sources. The numbers of insects captured at light traps, however, does not increase linearly with illumination, but rather it increases with the square root of the ratio of the illumination from the lamp to the background illumination [48] or as a function of the logarithm of the luminance as suggested by Stevens' power law [49] and its application to sensory phenomena in insects [50]. That is, a doubling of light intensity does not result in a doubling of insects captured at light traps, meaning the influence of the intensity of our lamps on insect attraction can be expected to be smaller than the absolute differences in luminance or illumination would suggest. In our results, therefore, the spectral composition of the lamps was significantly more important than the range in illumination produced (275–1830 lux).

The experiment was designed to focus on spectrum and not on light intensity because effect of intensity will not be the same across lamp types—every lamp of a particular spectral composition will have its own curve relating light intensity to insect attraction. For example, if the spectrum of a certain lamp attracts no insects, then insect attraction and intensity are independent variables and the slope of the curve will be zero. Conversely, this slope is expected to be positive for a different lamp emission spectrum that does attract insects. Thus, any model of insect attraction that incorporates light intensity must also incorporate the interaction spectral emissions and light intensity, and these models likely would differ for taxonomic groups. Our experimental design did not include sampling at different light intensities that would have been necessary to build such a model (the lamps A, B, C were tested at only one intensity each, and commercial CFL and LEDs at only two intensities each).

Our results should encourage continued research into the usefulness of insect spectral response curves to predict the number of arthropods attracted to lights. In previous research, when lamps with UV emissions were excluded, the attractiveness curves did not explain the number of insects captured at remaining light traps [14]. In contrast, we found that for some orders the attractiveness indices correlated well with arthropods captured for four LED lamps. Several issues arise with these results. First, despite the strong correlation between the bee attractiveness spectrum [31] and model coefficients indicating Lepidoptera attraction, both with and without CFLs, these correlations are with four or five values only and many more lamps should be compared. This line of enquiry is an important direction for future research. Second, we lack an explanation or mechanism to account for the superior performance of the bee attraction curve [31] compared with the moth attraction curve [40] in predicting moth attraction. Third, partial light response curves for a range of insects suggest that outside of the general patterns (i.e. most insects are attracted to blue and UV, but some orders are also attracted to red and green), species groups may each have distinctive patterns of attraction to light and it may be unwise to seek one response curve to guide development of lamps to minimize attraction of all insect groups. Beyond minimizing blue and eliminating UV, human exposure to insect vectors may require directed experiments with individual vector species.

The pattern of attraction of individuals by Order was more similar to that previously recorded in temperate zones than in the tropics. The most common Order collected in this study was Diptera, similar to results comparing different lamp types including LEDs in an agricultural setting in The Netherlands [14], along a river in Germany [9] and between a coniferous forest and coastal grassland in New Zealand [33], whereas a similar study in an urban tropical habitat in Brazil was dominated by Isoptera [15]. The relative contributions of different orders varied by lamp type, which supports order-specific analysis of attraction. Differences between orders is likely to be important relative to managing insect vectors, where attraction of Hemiptera and Diptera are exceedingly more important than attraction of Lepidoptera. Removing wavelengths that are attractive to moths may be insufficient to minimize risk of attracting vectors, and indeed, in this study, a custom 3500 K LED was almost as attractive to Diptera as was a 2700 K CFL, whereas the same custom LED was substantially less attractive to Lepidoptera than the CFL.

Overall, our results suggest that indoor lighting sources with full spectrum light can be designed to reduce insect attraction. Some trade-off in colour rendering index and lamp efficiency is probably necessary to minimize insect attraction, but values of our prototype examples were acceptable for indoor use. Our LEDs are tuneable through use of RGB and W diodes so the efficiency penalty normally associated with RGB lamps is offset by also using W to achieve the desired colour temperature. Use of a white diode along with RGB improves the colour rendering index, because colour rendering is related to continuity of the spectrum.

Although we did not identify to species and therefore did not document individual disease vectors, the results represent progress towards development of energy-efficient indoor lighting that has promise to reduce insect-borne disease while simultaneously providing high-quality light. Potential harm to humans arises from disease-vectoring insects that transmit life-threating diseases that are documented worldwide, especially in tropical environments where protection against insects is scarce and lights at night are necessary for habitation [51]. Malaria, leishmaniasis and Chagas disease are major diseases vectored by species of Diptera and Hemiptera that can be influenced by artificial lights [52]. Transmissions of these diseases vary with species of insects involved as well as intensity and spectrum of light [6]. Fly species (Phlebotomus spp.) responsible for transmitting leishmaniasis are attracted to lights, lending evidence that exterior lighting should be considered a risk factor [53], and the hemipteran vectors of Chagas disease (Triatoma spp., Paratiatoma spp. Reduviidae) are positively phototactic, so the importance of lighting as a continued research topic for vector borne disease is well established [6,52]. The connection between malaria and night lighting is still not fully understood, perhaps because light traps with a passive collection technique (e.g. pan traps) do not often capture mosquitos. Mosquitos do exhibit positive phototaxis, however, and are captured at lights with suction traps [6,54,55]. Disease transmission by mosquitos may, therefore, increase with artificial lighting [6], but this aspect has not yet been fully investigated. Further research into the relationship between spectral output of lamps and insect vectors is necessary to realize the potential of reducing exposure through better indoor (and outdoor) lighting.

The implications of night-time lighting for attraction of disease vectors [6], when combined with the expanding research on the effects of light on circadian rhythms and ecosystem functions [38,56–58], may persuade lighting engineers to follow a new standard that extends beyond display, price and durability, to include improved environmental and human health outcomes as well. Spectral characteristics that minimize insect attraction probably also reduce impacts on circadian rhythms, with its peak response to blue light [2]. We have demonstrated a proof-of-concept approach to minimize some of the ecological effects of both indoor and outdoor lighting installations by customizing lights to avoid sensitive portions of the visible spectrum, as has been suggested for ecological and chronobiological reasons [36,41,46]. Outdoor lighting, however, may need to be further restricted to avoid full spectrum lighting altogether to avoid adverse effects on human health, astronomical observation and ecosystems [36,41].


The evolution of light detection has allowed animals to monitor ambient brightness for circadian rhythms, determine the intensity of light from different directions for phototaxis, and form images for proper spatial vision 1 . With images, animals track and correct their own motion, target or avoid objects, and sometimes infer more elusive properties of a scene, such as object nearness or time until a collision. Although some animals achieve spatial vision without dedicated structures, like the diffuse photoreception of sea urchins 2 , overwhelmingly, acuity is captured by eyes, the diverse and convergently evolved organs that arrange screening pigments, optical lenses, and photoreceptors, to focus and capture images 3 . When light is sufficient, some estimate of its wavelength composition can improve object discrimination even under diverse or uneven lighting 4 . This perception of color requires photoreceptors with different wavelength sensitivities whose signals are then compared by underlying opponent processes 5 .

Wavelength sensitivities result largely (but not wholly) from a photoreceptor’s visual pigments, which are formed by joining a light-sensitive, retinal-based chromophore to an opsin, a seven-transmembrane-domain G protein-coupled receptor protein. When a chromophore responds to a photon absorption that changes its conformation, the opsin transduces this into a biologically meaningful signal by activating an internal G protein signaling cascade. Large-scale phylogenomic analyses have found many duplications and losses in the opsin protein family across invertebrates 6,7 . The water flea, Daphnia pulex possesses 46 opsins 8 , dragonflies have 15–33 opsins 9,10,11 and mantis shrimp have 12–33 opsins 12 . However, any more than four spectral channels offer diminishing returns in extracting information from natural scenes 13,14 , so why do some animals have so many opsins?

Since they regulate visual light transduction, opsins are subject to strong adaptive evolution, but they can also evolve through non-adaptive mechanisms. Non-adaptive forces usually cause random sequence evolution, and unless the duplicated opsins are co-opted for visual use, they usually become pseudogenes. Adaptive evolutionary forces are more likely to cause consistent, repeated, and persistent patterns of opsin retention and diversification 15 , such as with mate choice in guppies and butterflies 16,17 , flower foraging in bees and wasps 18 and changing light intensity environment with many nocturnal animals 19,20 .

Sensory modalities such as smell, electromagnetic reception, and touch can be more reliable than vision in dim environments 19 . Resource allocation trade-offs can cause a loss of stabilizing selection on genes of inefficient sensory systems, resulting in their downregulation or them becoming pseudogenes. This has been seen in nocturnal mammals 21 , cave-dwelling crayfish 22 , and deep-sea organisms 23,24,25 . If diminished light availability causes reduced opsin expression and loss, abundant light, conversely, may cause higher opsin expression, or prevent the loss of duplicated opsins and eventually lead to functional divergence. A comparison of visual genes between diurnal and nocturnal Lepidoptera revealed elevated opsin expression in the diurnal species 26 . Similarly, a study of opsin evolution across fireflies found higher amino acid transition rates in diurnal fireflies, across four independent diel switches 27 .

Lepidoptera opsin diversity has been studied in a handful of model taxa—mostly diurnal butterflies 26,28,29 —but has yet to be studied comprehensively across the entire order and multiple diel niches. Opsins are characterized by the wavelength to which their response is maximum (λmax). The λmax is sufficient to approximate the response curve of most opsins 30 . Lepidoptera opsins are usually classified as UV/RH4, Blue/RH5, and LW/RH6 opsins with corresponding maximal responses (λmax) in the ultraviolet (UV) (300–400 nm), blue (400–550 nm), and green/red (450–620 nm) wavelengths (LW). RH4–6 are implicated in color vision, but Lepidoptera also possess the non-visual RH7, which is associated with light sensing needed to maintain circadian rhythm 31 .

Earlier studies on Lepidoptera opsin evolution include work by Briscoe 28 , who analyzed the visual genes of eight Lepidoptera species including two moths, Xu et al. 32 , who analyzed 30 species including 12 moths, and Feuda et al. 31 who analyzed 10 species including four moths. However, due to small sample sizes, these studies had limited statistical power. They used gene trees instead of species trees for selection analyses, which, if different from the species tree topology, can bias results 33 . The few studies that examined opsin diversity and diel-niche association 31,32 compare butterflies and moths, effectively using only a single diel switch. But Lepidoptera have more than 100 recorded diel transitions 34 , and only by examining multiple independent diel-niche switches can we understand how light environment and diel-niche drive the evolution of their visual systems. To test if bright environments drive opsin diversification, we mine genomes and transcriptomes of 175 Lepidoptera species for visual opsins, combine our annotations with natural history diel-niche from the literature and map these traits onto a well resolved tree 35 to examine their evolution.

Polistes chinensis antennalis (Asian paper wasp)

The Asian paper wasp (Polistes chinensis antennalis) is native to areas of Japan and China and is currently a widespread introduced species in New Zealand. Research on its impact on native fauna is lacking but as it .

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CaptionPolistes chinensis antennalis (Asian paper wasp) close view of an adult on nest.
Copyright©Philip Spradbery
CaptionPolistes chinensis antennalis (Asian paper wasp) general view of nest with adults present.
Copyright©Philip Spradbery
CaptionPolistes chinensis antennalis (Asian paper wasp) adults on nest.
Copyright©Koji Tsuchida/Gifu University, Yanagido, Japan


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Summary of Invasiveness

The Asian paper wasp (Polistes chinensis antennalis) is native to areas of Japan and China and is currently a widespread introduced species in New Zealand. Research on its impact on native fauna is lacking but as it consumes insects it may potentially threaten native invertebrate species. It may also compete with native fauna for invertebrate and nectar resources.

Taxonomic Tree

  • Domain: Eukaryota
  • Kingdom: Metazoa
  • Phylum: Arthropoda
  • Subphylum: Uniramia
  • Class: Insecta
  • Order: Hymenoptera
  • Family: Vespidae
  • Genus: Polistes
  • Species: Polistes chinensis antennalis


Paper wasps are distinguished from vespulid wasps by their body shape. They have slender 13mm to 25mm reddish brown to black bodies with yellow rings and reddish areas on abdomen. Their wings are reddish or amber brown and they have long legs that especially noticeable in flight when they hang down.
Please see PaDIL (Pests and Diseases Image Library) Wasps: Asian paper wasp Polistes chinensis antennalis Perez for high quality diagnostic and overview images.


Native range: Eastern Asia, including parts of Japan and China ( Valentine and Walker 1991 ).
Known introduced range: Asian paper wasps are widespread in New Zealand ( Toft and Harris 2004 ).

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.



The Asian paper wasp frequently constructs its nest on man-made structures such as houses or other buildings ( Clapperton and Lo 1999 ). It commonly builds its nest in trees or bushes, usually on the branches, but sometimes on stems and leaves. Often nests are hidden inside dense shrubs, making them difficult to locate ( Toft and Harris 2004 ).
Large populations are more likely to develop in warm, lowland areas of open habitat, such as shrublands, swamps and salt meadows (Clapperton et al. 1996). Although the Asian paper wasp prefers to colonise urban habitats it may penetrate dense forests to establish nests near forest clearings (Clapperton, Tilley and Pierce 1996 ).
The Asian paper wasp’s native range in China and northern Japan includes areas where the winters can be severe the minimum threshold for egg development, however, is 14.8°C which may be a limiting factor to population growth ( Yoshikawa 1962 Valentine and Walker 1991 , Miyano 1981 , in Clapperton et al. 1996).

Habitat List

Terrestrial ManagedUrban / peri-urban areas Present, no further details Harmful (pest or invasive)
Terrestrial Natural / Semi-naturalWetlands Present, no further details Harmful (pest or invasive)
Terrestrial Natural / Semi-naturalScrub / shrublands Present, no further details Harmful (pest or invasive)

Host Animals

Biology and Ecology

Asian paper wasps prey on invertebrates and collect nectar and honeydew from flowers. Asian paper wasps rely heavily on the larvae and caterpillars of Lepidopteran insects (moths and butterflies) for their protein sources ( Rabb and Lawson 1957 Rabb 1960 ).

Over-wintering female wasps (which have been inseminated the preceding autumn) emerge in spring and begin nest cell construction and egg laying ( Kasuya 1983 Clapperton and Lo 1999 ). The first broods to emerge in late spring or early summer are comprised only of females ( Clapperton and Dymock 1997 ). There is no clear division into workers and queens and all females, even small ones, are potentially fertile ( Cumber 1951 ). Egg production in a colony is, however, dominated by one or only a few females ( Clapperton and Lo 1999 ). Males are produced from haploid eggs from early summer onwards and following the onset of production of male workers no more female progeny are produced for the season ( Cumber 1951 Clapperton and Dymock 1997 Clapperton and Lo 1999 ). Male wasps are particularly conspicuous in early autumn when they perform characteristic courtship behaviour ( Dymock 2000 ).

Means of Movement and Dispersal

Introduction pathways to new locations
Natural dispersal: Paper wasps are weak fliers. The maximum flight distance recorded is 72 m ( Suzuki 1978 )
Ship: Asian paper wasps may build their nests on shipping containers, ships or fishing vessels, potentially hitching a ride to anywhere on the globe ( Dymock 2000 ).

Local dispersal methods
Boat: Asian paper wasps may build their nests on shipping containers, ships or fishing vessels, potentially hitching a ride to anywhere on the globe ( Dymock 2000 ).
Natural dispersal (local)

Pathway Vectors

Impact Summary


The Asian paper wasp may consume a significant amount of invertebrate prey, putting prey species at direct risk of population decline, and indirectly threatening native insectivores by exerting competitive pressures on them (these may include native invertebrates or reptile species) ( Clapperton 1999 , Kleinpaste 2000 , in Toft and Harris 2004 ). For example, it may prey on larvae of native Lepidoptera species, such as the monarch butterfly (Danais plexippus), significantly reducing their population size. The Asia paper wasp may also compete with honeybees and native bird species for available honeydew and nectar resources (Clapperton et al. 1996). Secondary flow down effects are also possible from these disruptions to ecosystem processes is possible (ie: the disruption of pollination due to honeybee population decline).
The Asian paper wasp is a considerable public nuisance, stinging people when it is disturbed and constructing its nest on houses according to one survey they are held accountable for the greatest number of stings received in Auckland (Dymock et al. 1994, in Clapperton et al. 1996).

Similarities to Other Species/Conditions

The Australian paper wasp (Polistes humilis (Fab.)) has been in New Zealand since the 1880s ( Miller 1984 ). It has probably finished expanding its range, unless there are climatic or environmental changes.The two species are easily distinguished. P. c. antennalis is coloured black with yellow stripes while P. humilis is reddish-brown ( Clapperton et al. 1996 ).

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Preventative measures: The early detection of establishing populations is important as the next line of defence after initial quarantine procedures. Landcare Research has conducted research into generalised invertebrate surveillance techniques in recognition of the gap in biosecurity surveillance. These include malaise traps, mini-malaise traps, window traps, sticky traps, pitfall traps, UV light traps, flat ant traps, baited ant pottles, spurr wasp traps, ground bottle traps, yellow pan traps and beating. Of these, malaise traps, mini-malaise traps, window traps, sticky traps (for small wasps), UV traps, spurr wasp traps and ground bottle traps were found to be effective at catching wasps. Please follow this link for descriptions of trapping methods: .

Chemical: There are two ways of reducing a local wasp problem: either finding and destroying all nests in the area, or using poison bait ( Landcare Research 2007 ). Manual destruction of nests over large areas of shrub land is likely to be difficult and labour intensive ( Toft and Harris 2004 ). The advantage of poison bait is that foraging wasps carry the poison back to the nest, meaning it is unnecessary to locate nests or approach those that are very large or difficult to get at ( Landcare Research 2007 ). Unlike Vespula wasps, Polistes wasps are not attracted to dead bait (such as chicken meat or fish meat). This factor needs to be considered in any control strategy ( Toft and Harris 2004 ). On the other hand, the use of carbohydrate based bait is more likely to have negative impacts on non-target species such as honeybees (important pollinators) or and other native fauna ( Spurr 1996 , in Toft and Harris 2004 ). Manual destruction of nests over large areas of shrubland is apparently difficult and labour intensive ( Toft and Harris, 2004 ).
Both methods will only alleviate the problem for the current season and workers foraging for food will reinvade the area. The area will almost certainly be reinvaded next season by queen wasps, which can fly up to 30 kilometres in their search for suitable nesting sites ( Landcare Research 2007 ).


Clapperton, B. K. and Dymock, J. J. 1997. Growth and survival of colonies of the Asian paper wasp, Polistes chinensis antennalis (Hymenoptera: Vespidae), in New Zealand. New Zealand Journal of Zoology 24: 9-15.

Clapperton, B. K., and Lo, P. L. 2000. Nesting Biology of Asian Paper Wasps Polistes chinensis antennalis Perez, and Australian Paper Wasps P. humilis (Fab.) (Hymenoptera: Vesipade) in Northern New Zealand. New Zealand journal of Zoology, 27: 189-195.

Clapperton, B. K., Tilley, J. A. V. and Pierce, R. J. 1996. Distribution and abundance of Asian paper wasps Polistes chinensis antennalis Perez and Australian paper wasps P.humilis (Fab.) (Hymenoptera:Vespidae) in various habitats in New Zealand. New Zealand Journal of Zoology 23: 19-25

Clapperton, B.K. 1999. Abundance of Wasps and Prey Consumption of Paper Wasps (Hymenoptera, Vespidae: Polistinae) in Northland, New Zealand. New Zealand Journal of Ecology 23: 11-19.

Cumber, R. A. 1951. Some Observations on the Biology of the Australian Wasp, Polistes humilis Fabr. (Hymenoptera: Vespidae) in North Auckland (New Zealand), with Special Reference to the Nature of the worker caste. Proceedings of the Royal Entomological Society, London (A) 26: 11-16.

Dymock, J. J. 2000. Risk Assessment for Establishment of Polistine (Polistes spp.) and Vespine (Vespula spp.) Wasps on the Three Kings Islands in the Far North of New Zealand. Science for Conservation 156:18.

Dymock, J. J. Forgic, S. A. Ameratunga, R. 1994: A survey of wasp sting injuries in urban Auckland from December to April in 1991/2 and 1992/3. New Zealand Medical Journal 9 February: 32—33.

Harris, A., 2002 Paper Wasp heads South, in Stowaway Newsletter No.2 October 2002, Landcare Research, New Zealand

Harris, R J. and P.E.C. Read., 1999. Enhanced biological control of wasps. SCIENCE FOR CONSERVATION 115

Ito, Y. 1986. Spring Behaviour of an Australian Paper Wasp, Polistes humilis synoecus: Colony Founding by haplometrosis and Utilization of Old Nests. Kontyu 54: 191-202.

Kasuya, E., Hibino, Y., and Ito, Y. 1980. On “Intercolonial” Cannibalism in Japanese paper Wasps, Polistes chinensis antennalis Pérez and P. Jadwigale Dalla Torre (Hymenoptera: Vespidae). Researches on Population Ecology 22: 255-262.

Kasuya, E.1983. Social Behaviour of Early Emerging Males of a Japanese Paper Wasp, Polistes chinensis antennalis (Hymenoptera: Vespidae). Researches on Population Ecology 25:143-149.

Kudo, K. 2000. Variable investments in nests and worker production by the foundresses of Polistes chinensis (Hymenoptera : Vespidae). Journal of Ethology, 18, 37-41.

Kudo, K. 2005. Effects of body mass on nest and brood development in the paper wasp, Polistes chinensis (Hymenoptera : Vespidae). Sociobiology, 46, 647-654.

Landcare Research. 2007a. Home > Research > Biodoversity and Conservation > Invasive invertebrates > Identification & surveillance.

Landcare Research. 2007b. Home > Research > Biodoversity and Conservation > Invasive invertebrates > Wasps > Distribution> Distribution of Social Wasps in New Zealand.

Landcare Research. 2007c. Home > Research > Biodoversity and Conservation > Invasive invertebrates > Wasps > Impact in New Zealand.

Landcare Research. 2007d. Home > Research > Biodoversity and Conservation > Invasive invertebrates > Wasps > Wasp Control.

Rabb R.L. 1960. Biological studies of Polistes in North Carolina (Hymenoptera: Vespidae). Annals of the Entomological Society of America. 53:111–121. Find this article online

Rabb, R. L. & F. R. Lawson, 1957. Some factors influencing the predation of Polistes wasps on the tobacco hornworm. J. Econ. Entomol. 50: 778–784.

Spurr, E.B., 1996. Carbohydrate bait preferences of wasps (Vespula vulgaris and V. germanica) (Hymenoptera: Vespidae) in New Zealand. New Zealand Journal of Zoology 23: 315–324.

Suzuki, T. 1978. Area, efficiency and time foraging in Polistes chinensis antennalis Perez (Hymenoptera, Vespidae). Japanese Journal of Ecology, 28, 179-189.

Toft, R. J. and Harris, R. J. 2004. Short Communication: Can trapping control Asian paper wasp (Polistes chinensis antennalis) population? New Zealand. New Zealand Journal of Ecology 28(2): 272-282.

Valentine, E. W. and Walker, A. K. 1991. Annotated catalogue of New Zealand Hymenoptera. DSIR Plant Protection Report No. 4.

Walker, K. 2007. Asian paper wasp (Polistes chinensis antennalis) Pest and Diseases Image Library


Distribution References

CABI, Undated. Compendium record. Wallingford, UK: CABI

CABI, Undated a. CABI Compendium: Status inferred from regional distribution. Wallingford, UK: CABI

CABI, Undated b. CABI Compendium: Status as determined by CABI editor. Wallingford, UK: CABI

Principal Source


 Reviewed by: Jacqueline Beggs School of Biological Sciences, Tamaki Campus University of Auckland. New Zealand


Our results suggest that egg deposition by the pentatomid bug N. viridula stimulates production of host-induced synomones that attract the egg parasitoid T. basalis. Oviposition-induced synomones have been described in only two other tritrophic systems. First, oviposition by the elm leaf beetle Xanthogaleruca luteola Muller stimulates elm leaves(Ulmus minor Miller) to produce volatiles that attract the eulophid wasp Oomyzus gallerucae (Fonscolombe)(Meiners and Hilker, 1997). Second, oviposition by the pine sawfly Diprion pini (L.) induces odour production in needles of Pinus sylvestris L. to attract the eulophid wasp Chrysonotomyia ruforum (Krausse)(Hilker et al., 2002b). Although our results are not yet as extensive and detailed as in these two systems, several similarities and differences are already apparent.

Results on our tritrophic system show, for the first time, that annual plants can produce oviposition-induced synomones. As was suggested by Hilker et al. (2002a), annual plants,having a short life cycle and a relatively small biomass, may benefit more than larger perennial plants from egg parasitoid activity, which indirectly reduces the number of feeding larvae.

Synomones induced by oviposition by elm leaf beetle and pine sawfly, which have restricted host ranges, are characterized by a high specificity of response in their egg parasitoids (Hilker et al., 2002a). By contrast, N. viridula is highly polyphagous, developing on more than 150 species within ∼30 plant families, although it has a distinct preference for leguminous plants(Todd, 1989 Panizzi et al., 2000). We demonstrated that N. viridula oviposition apparently induced synomones in two different leguminous annual plants. Because of N. viridula's broad host range, we predict that synomones induced by N. viridula oviposition will be found in other annual and perennial host plants.

Unlike elm leaf beetle and pine sawfly, N. viridula females do not cut or otherwise physically damage the host substrate during oviposition. Instead, eggs are laid on the leaf surface in clusters that adhere to each other and to the plant by a sticky oviduct secretion. This secretion accumulates at the base of the egg while it descends the ovariole, and, once in contact with the air, the secretion rapidly oxidizes to a light brown film that extends over the egg mass border (Bin et al., 1993). Females of elm leaf beetle and pine sawfly also coat their eggs with oviduct secretion, with two resulting effects. First, the secretion induces production of synomones in the host plant when in contact with host tissues wounded during oviposition(Meiners and Hilker, 1997 Hilker et al., 2002b) elm leaf beetle females remove leaf lower surface prior to oviposition with their mouthparts, and pine sawfly females incise pine needles to insert the eggs(Meiners and Hilker, 2000 Hilker et al., 2002b). Second,the secretion is used as a contact kairomone that induces host acceptance behaviour in their egg parasitoids (Bin et al., 1993 Meiners and Hilker,1997).

To date, our experiments have not yet characterized the elicitor associated with N. viridula oviposition nor its specific mechanism of action. Because of the absence of any apparent plant injury at the time of oviposition, elicitors other than those associated with oviduct secretions may be possible, such as those associated with the surface chemistry of the eggs,as is the case with hydrocarbons present in the surface wax of Colorado potato beetle (Leptinotarsa decemlineata Say) eggs(Nelson et al., 2003), or even the presence of egg-associated microorganisms(Städler, 2002). Moreover, in the oviposition-induced synomone cases studied by Hilker et al.,the influence of adult feeding activity in inducing the synomones has been excluded (e.g. D. pini adult females do not feed on plants Hilker et al., 2002a). In our experiments, volatiles released by leaves damaged only by N. viridulafeeding activity were no more attractive than volatiles from undamaged leaves,but the volatiles produced by the combination of feeding damage and oviposition appeared to act synergistically. This synergistic activity between feeding and oviposition seems confirmed by the results of chemical and behavioural experiments currently in progress on the odours of bean plants induced by N. viridula adults as a result of their feeding activity,oviposition activity and feeding and oviposition activity combined (S. Colazza, J. S. McElfresh and J. G. Millar, personal observation). Synomones released as a response to attack by phytophagous insects could be produced or released at the site of the attack, as well as systemically by other parts of the plant, or the compounds could be produced at the site of the attack,transported to other sites and released far from the site of the attack(Dicke, 1999 Turlings and Benrey, 1998). All the oviposition-induced synomones investigated to date are emitted from both the leaves carrying the eggs and from insect- and egg-free parts of the same plant (Hilker et al.,2002a present study). A systemically induced response may benefit the plant under attack by increasing the amount of synomones produced and increasing the surface area from which the synomones are released, thus creating a more apparent signal that could increase parasitoid attraction(Dicke and van Loon, 2000 and references therein).

It has been shown that the release of host-induced synomones is timed as a consequence of several factors such as the cost of defence and/or synchronization with the wasp's activity(Turlings and Benrey, 1998). Host egg resources are ephemeral, because host egg quality rapidly decreases with time as the host develops (Vinson,1998). In our system, the age of host egg mass influences the acceptance behaviour of T. basalis(Bin et al., 1993). Therefore,it is expected that the production and/or activity of oviposition-induced synomones should be influenced by the age of the egg mass. Consistent with this hypothesis, leaves bearing eggs that are 72-96 h old still attract the parasitoid, while leaves bearing hatched eggs do not.

In conclusion, our knowledge of synomones induced in plants as a result of insect oviposition is still rudimentary, with the specific elicitors,synomones and mechanisms by which they work remaining to be identified. Work currently in progress aims to identify synomones induced by N. viridula oviposition and/or feeding and to examine the time course of their production as first steps in gaining a better understanding of the cues and signals mediating tritrophic interactions in this system.

These Carnivorous Plants Glow Under Ultraviolet Light to Attract Prey

It's long been known that carnivorous plants lure their insect prey in a range of ways: irresistible nectars, vivid colors and alluring scents that range from rose to rotten flesh.

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But recently, a group of scientists at the Jawaharlal Nehru Tropical Botanic Garden and Research Institute in India discovered a previously hidden means of beckoning among the most ruthless of greenery. Some carnivorous plants, they discovered, lure insects to their death with a fluorescent glow invisible to the human eye.

Sarracenia purpurea, a carnivorous plant native to the Eastern U.S., also glows under UV

Scientists believe that insects are attracted to carnivorous plants by the their odors and colors, but hard evidence as to what exactly lures the bugs to their deaths was previously unknown. In a stroke of serendipity, a team of scientists led by botanist Sabulal Baby put several carnivorous plants they'd been using for unrelated experiments under ultraviolet light, including Nepenthes khasiana, a rare pitcher plant native to India, and photographed what they saw.

"To our great surprise, we found a blue ring on on the pitcher rim," Baby says. "Then, we looked at other Nepenthes species and the prey traps of other carnivorous plants, including the Venus flytrap, and we consistently found UV-induced blue emissions." These colors, found in a total of twenty carnivorous plant species and documented in a study published in Plant Biology, were the first time such distinct fluorescent emissions were ever detected in the plant kingdom.

A pitcher plant under normal light (left) and UV light (right)

Under normal light, these bright, glowing rims would look green to humans. But an ant—which can't see red, but is extremely sensitive to blue and violet light—would see rings of blue florescence, the result of metabolic compounds in the plant that absorb UV radiation from the Sun and re-emit it as visible light. Putting the plants under a UV light in an otherwise dark room, as Baby's team did, amplifies the effect, allowing humans to more clearly see the blue emissions.

To prove that these emissions were involved in the plants' predation, the scientists constructed an elegant experiment. They monitored live pitcher plants in the field for a ten-day period, cutting them open afterward and seeing how many ants each one caught. Some of the plants, though, were painted with an acetone extract that blocks fluorescent emissions. It's not clear exactly why the ants would be attracted to the blue light, but the results, produced several times and in several different locations, pretty clearly indicate that it's the case:

The amount of insects caught over a ten-day period by a pitcher plant painted with a UV-masking compound (left) and a normal plant (right)

He has yet to test the idea, but Baby says that the plants might use their fluorescence for other purposes as well. Recent field studies in Borneo indicated that some species of pitchers may have a symbiotic relationship with small nocturnal mammals, such as rats, bats and tree shrews—these mammals come and drink nectar from the plants, and deposit nutritious feces nearby, which serve as a fertilizer. "Fluorescence emissions by Nepenthes traps could be acting as major visual cues luring these mammals towards them," Baby says.

These sorts of normally invisible signals could be way more prevalent in the plant kingdom than we previously realized. A recent study by British scientists, for instance, revealed that bumblebees can detect electric fields produced by flowers, adding another layer of communication to the symbiotic relationship between these two types of organisms. "There could be many other forms of signaling out there, waiting to be found," Baby says.

About Joseph Stromberg

Joseph Stromberg was previously a digital reporter for Smithsonian.

Fluorescent Geodes?

You might be surprised to learn that some people have found geodes with fluorescent minerals inside. Some of the Dugway geodes, found near the community of Dugway, Utah, are lined with chalcedony that produces a lime-green fluorescence caused by trace amounts of uranium.

Dugway geodes are amazing for another reason. They formed several million years ago in the gas pockets of a rhyolite bed. Then, about 20,000 years ago they were eroded by wave action along the shoreline of a glacial lake and transported several miles to where they finally came to rest in lake sediments. [4] Today, people dig them up and add them to geode and fluorescent mineral collections.

UV lamps: Three hobbyist-grade ultraviolet lamps used for fluorescent mineral viewing. At top left is a small "flashlight" style lamp that produces longwave UV light and is small enough to easily fit in a pocket. At top right is a small portable shortwave lamp. The lamp at bottom produces both longwave and shortwave light. The two windows are thick glass filters that eliminate visible light. The larger lamp is strong enough to use in taking photographs. UV-blocking glasses or goggles should always be worn when working with a UV lamp.

Light Environments Differently Affect Parasitoid Wasps and their Hosts’ Locomotor Activity

In natural environments, organisms must adapt to changing light conditions. Significant research has been done on diurnal pollinating insects’ vision. However, little is known on parasitoid insects. Here, we studied how locomotor activity of the parasitoid wasp Aphidius ervi and its main host, the pea aphid Acyrthosiphon pisum, is affected under controlled artificial illumination. Using LEDs of 5 different wavelengths (361, 450, 500-600, 626 and 660 nm), we created different artificial light spectra that parasitoids and host aphids can encounter in natural environment including leaf-shade and direct sunlight. We found that pea aphid probability of walking depended on interactions between illumination, developmental stage and genotype as expressed in clonal variation. Artificial light intensity did not affect the parasitoid’s probability of walking as opposed to wavelength, and activity depended on the sex of individuals. Males were more active than females under all monochromatic wavelength spectra tested. Virgin females were much less active under the artificial leaf-shade illumination and artificial sunlight, as compared to males and mated females. Delay before flight for females was favored by sunlight illumination whereas the light environment did not affect flight delay for males. We demonstrated that locomotor activity of A. pisum (walking) and of A. ervi (walking and flight) vary according to the light environment. This study should help develop better understanding of the effects of illumination on host-parasitoid interactions, which in turn may help control insect pest populations.

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How light from street lamps and trees influence the activity of urban bats

Artificial light is rightly considered a major social, cultural and economic achievement. Yet, artificial light at night is also said to pose a threat to biodiversity, especially affecting nocturnal species in metropolitan areas. It has become clear that the response by wildlife to artificial light at night might vary across species, seasons and lamp types. A study conducted by a team led by the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) sheds new light on how exactly ultraviolet (UV) emitting and non-UV emitting street lamps influence the activity of bats in the Berlin metropolitan area and whether tree cover might mitigate any effect of light pollution. The study is published in the scientific journal Frontiers in Ecology and Evolution.

Natural sunlight sets the pace of day and night on our planet. Over millions of years, wildlife and people have adapted to the rhythm of the natural photoperiod. As creatures of daytime, humans have expanded their ecological niche into night-time by inventing and using artificial light. Yet nocturnal animals such as bats may suffer from the detrimental effects of artificial light generated by street lamps, a phenomenon now recognised as light pollution. As it turns out, bat responses to light pollution were complex. "We observed a higher activity of two pipistrelle bat species, the common pipistrelle and Nathusius' pipistrelle, in areas with high numbers of UV emitting street lamps," explains Tanja Straka, scientist at the IZW's Department of Evolutionary Ecology and first author of the study. These opportunistic species may feed on insects that are attracted to UV emitting lamps. "However, all other species were less active at and even repelled by the lamps, irrespective of whether the light they emitted did or did not contain UV light," adds Straka.

The novelty of this study is that these effects were considered in relation to tree cover. Not only do trees provide bats with shelter during daytime, trees may also provide shade for bats in illuminated areas. "Our goal was to determine whether and how tree cover influences any responses of bats to artificial light," says Straka.

The team found that the response of bats to artificial light was intensified in areas with high tree cover. For example, the attraction of Pipistrellus pipistrellus to UV light was more pronounced when many trees were present, probably because UV light attracted insects from the vegetation. On the other hand mouse-eared bats (Myotis spp.) were less frequently recorded in areas with a high number of street lamps (irrespective of UV or no UV emission) and lots of trees. Mouse-eared bats seem to be particularly light-sensitive and avoid illuminated areas even when these include trees or shrubs. The team also found that high-flying insectivorous bats were more active in areas when the light emission from LED street lanterns was dampened by a high tree coverage than in areas with many LED lanterns and no trees." LED lights do not attract large numbers of insects and therefore they are not attractive as foraging grounds for high-flying bats they might even be repelled by light spillover from LED lamps. Tree cover seems to reduce light spillover, which enable high-flying bats to fly in the shadow of the tree canopy," Straka explains.

These results are based on the analysis of more than 11,000 bat calls recorded during three months at 22 sites in the Berlin city area. Bat calls were identified by species and the activity of bats was calculated for each species and site. These data were compared with features of the landscape, such as tree cover and the intensity of light pollution as estimated by remote sensing (i.e. satellite based data). In addition, the exact location of street lamps and information on UV light emission was used to estimate the level of light pollution in the study area.

"The bottom line is that for bats the relation between artificial light and vegetation is complex and it varies between species, yet overall artificial light at night has negative consequences for bats," concludes Christian Voigt, the Head of Department. "Even those species that may hunt at street lamps opportunistically will suffer on the long run from the constant drain of insects dying at street lamps. Trees are important for urban bats, not only as a shelter but also as a source for prey insects. Hence artificial light should be avoided in habitats with many trees." Adding trees in highly lit areas or turning off lights when the area is not in use could substantially contribute to the conservation of bats and possibly also other nocturnal wildlife, because trees provide shade and refuge that bats urgently need.

LED-lighting influences the activity of bats

The widespread replacement of conventional bulbs in street lighting by energy-saving light-emitting diodes (LEDs) has considerable influence on bats as urban nocturnal hunters. Opportunistic bats lose hunting opportunities whereas light sensitive species benefit. This was shown in a recent study by Christian Voigt and Daniel Lewanzik from the Leibniz Institute for Zoo and Wildlife Research (IZW).

Conventional high pressure mercury bulbs have a broad spectrum of wavelengths, including those in the ultraviolet range. As a consequence, insects are magically attracted to street lighting and indirect light spilling out from houses. Moths, mosquitoes, beetles and other insects are drawn to the light because of the so-called vacuum cleaner effect. They circle around lamps and often become victims of insect-eating predators. For instance, some light-tolerant bat species frequently forage on insect aggregations at lights for them street lamps are a lit "buffet." Yet, the new LEDs that are used in street lamps do not emit UV light. Thus, insects ignore them and do not buzz around the lamps anymore. The scientists from IZW therefore studied how the increasing use of LED light bulbs may influence the activity of urban bats.

Previously, it was well known that opportunistic species such as pipistrelles and the common noctule tolerate light and hunt even in lit areas in cities at night. Light sensitive species that shun the light such as many mouse-eared bats mainly hunt in dark parks and forests.

For their study, part of the so-called "Loss of the night" project funded by the German Federal Ministry of Education and Research (BMBF), the scientists installed bat recorders on 46 street lamps in six German cities, amongst them Freiburg in the southwest and Berlin. By recording echolocation calls of hunting bats, bat recorders automatically detect the presence of bats at conventional and LED street lamps.

The results were interesting: whereas the activity of the common pipistrelle diminished by 45 % near LED lamps, light sensitive species that usually avoid artificial light increased their activity by a factor of four-and-a-half. A few species such as the Nathusius pipistrelle were not affected at all by the reduced spectrum of wave lengths of the LEDs. "We therefore conclude that bats which are sensitive to light might benefit from the increasing use of LED, but opportunistic species will suffer from it," says Voigt. The latter will probably have to travel longer distances in order to find sufficient food.

One thing seems to be sure: Bats will adjust their foraging behaviour to the new situation and, therefore, the composition of species within local bat assemblages is likely to change in urban environments. "Both the use of LED lights and the change in activity of bats will have a substantial effect on insect populations, since bats are the top predators for insect populations in the urban environment," emphasises Voigt.

Will there be more mosquitoes and other insect nuisances in the future? "Yes, this might be the negative side of it," speculates Voigt. "But there will also be more moths, and thus more pollinators!" More pollinators will also mean a higher production of seeds, to the benefit of plants -- an effect that probably no one had thought of when the purpose was to save energy in street lighting.

LEDs use very little energy, thus electricity costs are low. Further, they can be controlled dynamically and dimmed when full intensity is not needed. This sounds like a big benefit -- yet it might also turn into a problem. The tendency of people to use LEDs to light every little corner of their house and garden is likely to wipe out any potential energy savings.

This also leads to a steady increase in light pollution. The negative effects of light pollution on human health are already well documented.

"Humans are diurnal creatures and their day-night-rhythm is set by the secretion of hormones such as melatonin," says Voigt. Numerous studies provide evidence that people working in night shifts have a higher risk of contracting certain types of cancer because artificial light interferes with their biorhythm.

"Meanwhile scientists are seeing more clearly that artificial light does not only affect people but also wildlife and even whole ecosystems," highlights Christian Voigt.

In November 2016, EUROBATS, an EU-group of experts, will meet at the IZW in Berlin to share their experiences on how bats are affected by artificial light in different EU countries hopefully this will result in a list of recommendations on how to use artificial light in a wildlife-friendly way. "A general rule is: the less artificial light, the better. One should question the necessity of every single lamp," Voigt states.

Urban bats have to cope with a double whammy. Not only do some of them lose their hunting opportunities when insects are no longer attracted to street lanterns, but many also lose their roosting sites because of the current promotion of energy efficient houses and with it the efficient insulation of their walls, exterminating bat roosts in buildings.

Watch the video: Καταπολέμηση σφηκών και κηροσκόρου. Μελισσοκομος ε; 35 (October 2022).