The evolution of color vision in insects

High toxin concentration in pollen may deter collection by bees in butterfly-pollinated Rhododendron molle

BACKGROUNDS AND AIMS

The hypothesis that plants evolve features that protect accessible pollen from consumption by flower visitors remains poorly understood.

METHODS

To explore potential chemical defence against pollen consumption, we examined the pollinator assemblage, foraging behaviour, visitation frequency and pollen transfer efficiency in Rhododendron molle, a highly toxic shrub containing rhodojaponin III. Nutrient (protein and lipid) and toxic components in pollen and other tissues were measured.

KEY RESULTS

Overall in the five populations studied, floral visits by butterflies and bumblebees were relatively more frequent than visits by honeybees. All foraged for nectar but not pollen. Butterflies did not differ from bumblebees in the amount of pollen removed per visit, but deposited more pollen per visit. Pollination experiments indicated that R. molle was self-compatible, but both fruit and seed production were pollen-limited. Our analysis indicated that the pollen was not protein-poor and had a higher concentration of the toxic compound rhodojaponin III than petals and leaves, this compound was undetectable in nectar.

CONCLUSION

Pollen toxicity in Rhododendron flowers may discourage pollen robbers (bees) from taking the freely accessible pollen grains, while the toxin-free nectar rewards effective pollinators, promoting pollen transfer. This preliminary study supports the hypothesis that chemical defence in pollen would be likely to evolve in species without physical protection from pollinivores.

Rapid screening for resistance to Sitobion avenae (F.) and Rhopalosiphum padi (L.) in winter wheat seedlings and selection of efficient assessment methods

BACKGROUND

Sitobion avenae (F.) and Rhopalosiphum padi (L.) are harmful pests of wheat [Triticum aestivum (L.)]. No genetic resistance against the aphids has been identified in commercial wheat varieties and resistance phenotyping can be time-consuming and laborious. Here, we tested a high-throughput phenotyping method to screen 29 commercial winter wheat varieties for alate antixenosis and antibiosis. We validated this method using comprehensive behavioural analyses, including alate attraction to volatile organic compounds (VOCs) and a feeding bioassay using an electrical penetration graph (EPG), subsequently highlighting possible sources of resistance.

RESULTS

We observed differences in alate behaviour upon assessing alate settlement on wheat seedlings and attraction towards VOCs, revealing the importance of visual and early post-alighting cues for alate host selection. Aphid settlement was four times higher on the most preferred variety than on the least preferred variety. Using an EPG bioassay, we identified phloem feeding and stylet derailment parameters linked to resistance. We found antibiosis assessment on detached leaves to be an inadequate screen because it produced results inconsistent with intact leaves assessment. Alate and nymph mortality were identified as key traits signifying antibiosis, showing significant positive relationships with alate reproduction and nymph mean relative growth rate.

CONCLUSIONS

Overall, antixenosis and antibiosis varietal responses were consistent for both aphid species. Alate settlement on wheat seedlings was a more efficient antixenosis screen than an olfactometer assay using VOCs. In addition to assessing alate and nymph survival for antibiosis, this allows for more rapid phenotyping of large numbers of genotypes to identify novel aphid resistance genes for varietal improvement. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Experimental elevated temperature affects bumblebee foraging and flight speed

Global warming threatens wild bees and their interaction with plants. While earlier studies have highlighted the negative effects of elevated temperatures on bee-plant interactions, we still lack knowledge about how they impact the foraging behaviours that are central to bee pollination activities. To address this knowledge gap, we investigated how ambient temperature affected the foraging behaviours of the bumblebee Bombus terrestris. We allowed the bumblebees to forage freely on artificial flowers in two climate-controlled rooms set at 24°C and 32°C. The colonies were alternated between the two temperatures every week. We recorded the flower visitation rate, flight speed, total foraging time and number of foraging trips. In addition, we measured flight metabolic rate across a range of temperatures to assess its potential as an underlying mechanism. In comparison to 24°C, at 32°C, flower visitation time decreased while flower visitation rate and flight speed increased. This is consistent with the reduction in flight metabolic rate recorded between these temperatures. At 32°C, the number of trips made by each worker decreased, suggesting that, despite the reduced energetic cost, flight in elevated temperatures may be stressful. Our results suggest that elevated temperatures affect bumblebee foraging behaviour and that this would likely disrupt plant-insect interactions.

The role of pigments in light color variation of the firefly Photinus pyralis

Fireflies use bioluminescent signals to communicate with their mates. Luciferase has been thought to be the sole contributor to light color; however, populations of the Photinus pyralis firefly display variation in the color of their emitted signals yet have identical luciferase sequences. Here, we examined whether pigments could be present in the light organs of the twilight-active species P. pyralis and contribute to this variation. We detected patterns of expression that suggest ommochrome and pterin screening pigments are expressed in P. pyralis light organs and could filter light emitted by luciferase and play a role in signal tuning. There were no significant differences between the pigment gene expression of P. pyralis individuals with yellower and greener signals. Our study provides alternative mechanisms that could influence pigments in P. pyralis light organs that could also play a role in modifying signal color.

Are phlebotomine sand flies (Diptera: Psychodidae) really attracted to UV-light sources?

Phlebotomine sand flies are the sole confirmed vector of leishmaniosis, a group of endemic and re-emerging diseases in southern European countries such as Spain. Light traps are the major surveillance method currently being employed. Nevertheless, color light attraction by sand flies remains mostly unknown. Following prior research, the effect of UV-LED light sources, and its synergic effect with different color lights has been evaluated employing a modified Flebocollect (FC) light trap model. Results suggest that female Phlebotomus perniciosus sand flies are more attracted to a FC trap lured with the combination of blue and UV LED light sources than commercial CDC (Center for Disease Control and prevention) traps (Bonferroni post-hoc test; p < 0.08; blue/UV mean = 0.50; CDC mean = 0.13), while the combination of red and UV modified-traps excel in capturing Sergentomyia minuta sand flies (Bonferroni post-hoc test; p < 0.04; blue/UV mean = 1.19; CDC mean = 0.66). However, based on our prior studies, incorporating UV light sources into sand fly traps does not seem to enhance their attractiveness, as it has not resulted in higher capture rates. These findings contribute to understanding how sand flies' vision and light color detection is. Further research is recommended to standardize trap construction procedures and explore variations in different endemic regions according to different sand fly species.

Localized and Long-Lasting Adaptation in Dragonfly Target-Detecting Neurons

Some visual neurons in the dragonfly (Hemicordulia tau) optic lobe respond to small, moving targets, likely underlying their fast pursuit of prey and conspecifics. In response to repetitive targets presented at short intervals, the spiking activity of these "small target motion detector" (STMD) neurons diminishes over time. Previous experiments limited this adaptation by including intertrial rest periods of varying durations. However, the characteristics of this effect have never been quantified. Here, using extracellular recording techniques lasting for several hours, we quantified both the spatial and temporal properties of STMD adaptation. We found that the time course of adaptation was variable across STMD units. In any one STMD, a repeated series led to more rapid adaptation, a minor accumulative effect more akin to habituation. Following an adapting stimulus, responses recovered quickly, though the rate of recovery decreased nonlinearly over time. We found that the region of adaptation is highly localized, with targets displaced by ∼2.5° eliciting a naive response. Higher frequencies of target stimulation converged to lower levels of sustained response activity. We determined that adaptation itself is a target-tuned property, not elicited by moving bars or luminance flicker. As STMD adaptation is a localized phenomenon, dependent on recent history, it is likely to play an important role in closed-loop behavior where a target is foveated in a localized region for extended periods of the pursuit duration.

A visual pollination mechanism of a new specialized pollinating weevil-plant reciprocity system

Introduction

Pollinating flower-consuming mutualisms are considered exemplary models for studying coevolution due to their rarity. Visual cues are considered to have a major role in facilitating the evolution of floral patterns in these systems. We present a new specialized pollinating flower-consuming mutualism from the plant Wurfbainia villosa, which is a traditional Chinese herbal medicine, by a pollinating weevil, Xenysmoderes sp.

Methods

In this study, We utilized monochrome plates for binary-choice tests to determine weevil color preferences, conducted behavioral choice experiments, using trackballs, photographed flowers and weevils, and employed blue sticky boards to attract weevils in the field.

Results

Tests were conducted using colorpreferring weevils in both indoor and outdoor field systems, and validation experiments were performed. Behavioral tests were conducted to investigate the role of the visual cues in the pollinator attraction of W. villosa, which is a selfcompatible insect-pollinated plant that relies primarily on the Xenysmoderes sp. weevil for pollination due to its specialized gynandrium-like structure. Behavioral tests demonstrated that a blue color wavelength of 480 nm and the blue color system, as along with the UV-style pattern of the flowers, particularly the parts with specialized gynandrium-like structures in the labellum, were significantly attractive to both male and female weevils. These results were further confirmed through the field blue sticky board trap method.

Discussion

These findings indicated that the interaction between W. villosa and Xenysmoderes sp. weevil was a novel symbiotic relationship involving pollinator flower consumption. Additionally, Wurfbainia villosa flowers developed specific visual cues of UV patterns and specialized structures that played a crucial role in attracting pollinators.

The Carotenoid Composition of Larvae Feed Is Reflected in Adult House Fly (Musca domestica) Body

Carotenoids are common and diverse organic compounds with various functional roles in animals. Except for certain aphids, mites, and gall midges, all animals only acquire necessary carotenoids through their diet. The house fly (Musca domestica) is a cosmopolitan pest insect that populates diverse habitats. Its larvae feed on organic substrates that may vary in carotenoid composition according to their specific content. We hypothesized that the carotenoid composition in the adult house fly's body would reflect the carotenoid composition in the larval feed. House fly larvae were reared on diets that differed in carotenoid composition. HPLC analysis of the emerging adult flies indicate that the carotenoid composition of adult house flies is related, but not identical, to the carotenoid composition in its natal substrate. These findings may be developed to help identify potential sources of house fly infestations. Also, it is recommended that rearing substrates of house fly larvae, used for animal feed, should be carefully considered.

The modelling of flower colour: spectral purity or colour contrast as biologically relevant descriptors of flower colour signals for bees depending upon the perceptual task

Flower colour is an important mediator of plant-pollinator interactions. While the reflectance of light from the flower surface and background are governed by physical properties, the perceptual interpretation of such information is generated by complex multilayered visual processing. Should quantitative modelling of flower signals strive for repeatable consistency enabled by parameter simplification, or should modelling reflect the dynamic way in which bees are known to process signals? We discuss why colour is an interpretation of spectral information by the brain of an animal. Different species, or individuals within a species, may respond differently to colour signals depending on sensory apparatus and/or individual experience. Humans and bees have different spectral ranges, but colour theory is strongly rooted in human colour perception and many principles of colour vision appear to be common. We discuss bee colour perception based on physiological, neuroanatomical and behavioural evidence to provide a pathway for modelling flower colours. We examine whether flower petals and floral guides as viewed against spectrally different backgrounds should be considered as a simple colour contrast problem or require a more dynamic consideration of how bees make perceptual decisions. We discuss that plants such as deceptive orchids may present signals to exploit bee perception, whilst many plants do provide honest signalling where perceived saturation indicates the probability of collecting nutritional rewards towards the centre of a flower that then facilitates effective pollination.

Flower reflectance and floral traits data from Ökologisch-Botanischer Garten (OBG), Germany

Not all colours are perceived and interpreted equally. The electromagnetic spectrum is perceived differently by the distinct visual systems of animal species, resulting in differences in each species' colour perception. Given the diverse colours found in flowering plants, it is interesting to consider the colour perception of insects and the co-evolution of flowering plants to attract pollinators. Here, we considered the differences between human visual systems and that of bees and flies-the two largest insect pollinator groups. We collected flower reflectance spectral data of 73 species across seven human-perceived colours using a spectrophotometer. Minimum of 3 different flowers were used to measure the reflectance properties of flower colours. The raw data can be used to visualize the different animals' visual systems i.e. it can be processed and translated into known photoreceptors of human, bee, and fly visual systems. Overall, our data will help to compare how different animals see flower colours in the natural world and will also highlight the importance of understanding the interspecific communication in plant-pollinator communities. Thus, our data will assist scientists in the future to recognize the floral colour evolution in angiosperms.

Multifunctionality of angiosperm floral bracts: a review

Floral bracts (bracteoles, cataphylls) are leaf-like organs that subtend flowers or inflorescences but are of non-floral origin; they occur in a wide diversity of species, representing multiple independent origins, and exhibit great variation in form and function. Although much attention has been paid to bracts over the past 150 years, our understanding of their adaptive significance remains remarkably incomplete. This is because most studies of bract function and evolution focus on only one or a few selective factors. It is widely recognised that bracts experience selection mediated by pollinators, particularly for enhancing pollinator attraction through strong visual, olfactory, or echo-acoustic contrast with the background and through signalling the presence of pollinator rewards, either honestly (providing rewards for pollinators), or deceptively (attraction without reward or even trapping pollinators). However, studies in recent decades have demonstrated that bract evolution is also affected by agents other than pollinators. Bracts can protect flowers, fruits, or seeds from herbivores by displaying warning signals, camouflaging conspicuous reproductive organs, or by providing physical barriers or toxic chemicals. Reviews of published studies show that bracts can also promote seed dispersal and ameliorate the effects of abiotic stressors, such as low temperature, strong ultraviolet radiation, heavy rain, drought, and/or mechanical abrasion, on reproductive organs or for the plants' pollinators. In addition, green bracts and greening of colourful bracts after pollination promote photosynthetic activity, providing substantial carbon (photosynthates) for fruit or seed development, especially late in a plant's life cycle or season, when leaves have started to senesce. A further layer of complexity derives from the fact that the agents of selection driving the evolution of bracts vary between species and even between different developmental stages within a species, and selection by one agent can be reinforced or opposed by other agents. In summary, our survey of the literature reveals that bracts are multifunctional and subject to multiple agents of selection. To understand fully the functional and evolutionary significance of bracts, it is necessary to consider multiple selection agents throughout the life of the plant, using integrative approaches to data collection and analysis.

Investigating the Influence of Varied Light-Emitting Diode (LED) Wavelengths on Phototactic Behavior and Opsin Genes in Vespinae

The phototactic behavior of insects is commonly used to manage pest populations in practical production. However, this elusive behavior is not yet fully understood. Investigating whether the opsin genes play a crucial role in phototaxis is an intriguing topic. Vespinae (Hymenoptera: Vespidae) are a common group of social wasps that are closely associated with human activities. Efficiently controlling wasp populations while maintaining ecological balance is a pressing global challenge that still has to be resolved. This research aims to explore the phototactic behavior and key opsin genes associated with Vespinae. We found significant differences in the photophilic rates of Vespula germanica and Vespa analis under 14 different light conditions, indicating that their phototactic behavior is rhythmic. The results also showed that the two species exhibited varying photophilic rates under different wavelengths of light, suggesting that light wavelength significantly affects their phototactic behavior. Additionally, the opsin genes of the most aggressive hornet, Vespa basalis, have been sequenced. There are only two opsin genes, one for UV light and the other for blue light, and Vespa basalis lacks long-wavelength visual proteins. However, they exhibit peak phototaxis for long-wavelength light and instead have the lowest phototaxis for UV light. This suggests that the visual protein genes have a complex regulatory mechanism for phototactic behavior in Vespinae. Additionally, visual protein sequences have a high degree of homology among Hymenoptera. Despite the hypotheses put forward by some scholars regarding phototaxis, a clear and complete explanation of insect phototaxis is still lacking to date. Our findings provide a strong theoretical basis for further investigation of visual expression patterns and phototactic mechanisms in Vespinae.

Opsin diversity and evolution in the Elateroidea superfamily: Insights from transcriptome data

Vision plays a vital biological role in organisms, which depends on the visual pigment molecules (opsin plus chromophore). The expansion or reduction of spectral channels in the organisms is determined by distinct opsin classes and copy numbers resulting from duplication or loss. Within Coleoptera, the superfamily Elateroidea exhibits a great diversity of morphological and physiological characteristics, such as bioluminescence, making this group an important model for opsin studies. While molecular and physiological studies have been conducted in Lampyridae and Elateridae, other families remain unexplored. Here, we reused transcriptome datasets from Elateroidea species, including members of Elateridae, Lampyridae, Phengodidae, Rhagophthalmidae, Cantharidae, and Lycidae, to detect the diversity of putative opsin genes in this superfamily. In addition, we tested the signature of sites under positive selection in both ultraviolet (UV)- and long-wavelength (LW)-opsin classes. Although the visual system in Elateroidea is considered simple, we observed events of duplication in LW- and UV-opsin, as well as the absence of UV-opsin in distinct families, such as larval Phengodidae individuals. We detected different copies of LW-opsins that were highly expressed in the eyes of distinct tribes of fireflies, indicating the possible selection of each copy during the evolution of the sexual mating to avoid spectrum overlapping. In Elateridae, we found that the bioluminescent species had a distinct LW-opsin copy compared with the non-bioluminescent species, suggesting events of duplication and loss. The signature of positive selection showed only one residue associated with the chromophore binding site in the Elateroidea, which may produce a bathochromic shift in the wavelength absorption spectra in this family. Overall, this study brings important content and fills gaps regarding opsin evolution in Elateroidea.

UV reflectance in crop remote sensing: Assessing the current state of knowledge and extending research with strawberry cultivars

Remote sensing of spectral reflectance is a crucial parameter in precision agriculture. In particular, the visual color produced from reflected light can be used to determine plant health (VIS-IR) or attract pollinators (Near-UV). However, the UV spectral reflectance studies largely focus on non-crop plants, even though they provide essential information for plant-pollinator interactions. This literature review presents an overview of UV-reflectance in crops, identifies gaps in the literature, and contributes new data based on strawberry cultivars. The study found that most crop spectral reflectance studies relied on lab-based methodologies and examined a wide spectral range (Near UV to IR). Moreover, the plant family distribution largely mirrored global food market trends. Through a spectral comparison of white flowering strawberry cultivars, this study discovered visual differences for pollinators in the Near UV and Blue ranges. The variation in pollinator visibility within strawberry cultivars underscores the importance of considering UV spectral reflectance when developing new crop breeding lines and managing pollinator preferences in agricultural fields.

Identification, expression analysis, and functional verification of three opsin genes related to the phototactic behaviour of Ostrinia furnacalis

Ostrinia furnacalis is a disreputable herbivorous pest that poses a serious threat to corn crops. Phototaxis in nocturnal moths plays a crucial role in pest prediction and control. Insect opsins are the main component of insect visual system. However, the inherent molecular relationship between phototactic behaviour and vision of insects remains a mystery. Herein, three opsin genes were identified and cloned from O. furnacalis (OfLW, OfBL, and OfUV). Bioinformatics analysis revealed that all opsin genes had visual pigment (opsin) retinal binding sites and seven transmembrane domains. Opsin genes were distributed across different developmental stages and tissues, with the highest expression in adults and compound eyes. The photoperiod-induced assay elucidated that the expression of three opsin genes in females were higher during daytime, while their expression in males tended to increase at night. Under the sustained darkness, the expression of opsin genes increased circularly, although the increasing amplitude in males was lower when compared with females. Furthermore, the expression of OfLW, OfBL, and OfUV was upregulated under green, blue, and ultraviolet light, respectively. The results of RNA interference showed that the knockout of opsin genes decreased the phototaxis efficiency of female and male moths to green, blue, and ultraviolet light. Our results reveal that opsin genes are involved in the phototactic behaviour of moths, providing a potential target gene for pest control and a basis for further investigation on the phototactic behaviour of Lepidoptera insects.

Response of Hypothenemus hampei Ferrari (Coleoptera: Curculionidae: Scolytinae) parasitized by the nematode Metaparasitylenchus hypothenemi Poinar (Tylenchida: Allantonematidae) to different colors of light

Metaparasitylenchus hypothenemi is a nematode that naturally parasitizes Hypothenemus hampei in a coffee-producing region in Chiapas, Mexico. This study investigated changes in the attraction of parasitized borers to light. We compared the attraction of adult H. hampei females (parasitized and uninfected) to 14 different light wavelengths (350-670 nm) with a control (570 nm, yellow) under laboratory conditions. The response ranges of non-parasitized and parasitized borers were 370-650 nm and 340-650 nm, respectively. The attraction curve showed a similar shape in both borer groups (parasitized and non-parasitized), but a wide wavelength range (380-590 nm) attracted more parasitized than non-parasitized borers. The maximum response of the uninfected borers occurred at 520 nm (green), while parasitized borers exhibited three response peaks (380 nm, violet; 460 nm, blue; 520 nm, green). Parasitized borers were significantly more attracted to green light (520 nm) than to the control. The altered attraction to light in borers parasitized by M. hypothenemi is discussed from the perspective of possible host manipulation and the natural prevalence of this parasite.

Optimising the colour of traps requires an insect's eye view

Colour is a critical property of many traps used to control or monitor insect pests, and applied entomologists continue to devote time and effort to improving colour for greater trapping efficiency. This work has often been guided by human colour perceptions, which differ greatly from those of the pests being studied. As a result, trap development can be a laborious process that is heavily reliant on trial and error. However, the responses of an insect's photoreceptors to a given trap colour can be calculated using well-established procedures. Photoreceptor responses represent sensory inputs that drive insect behaviour, and if their relationship to insect attraction can be determined or hypothesised, they provide metrics that can guide the rational optimisation of trap colour. This approach has recently been used successfully in separate studies of tsetse flies and thrips, but could be applied to a wide diversity of pest insects. Here we describe this approach to facilitate its use by applied entomologists. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Quantity misperception by hymenopteran insects observing the solitaire illusion

Visual illusions are errors in signal perception and inform us about the visual and cognitive processes of different animals. Invertebrates are relatively less studied for their illusionary perception, despite the insight that comparative data provides on the evolution of common perceptual mechanisms. The Solitaire Illusion is a numerosity illusion where a viewer typically misperceives the relative quantities of two items of different colors consisting of identical quantity, with more centrally clustered items appearing more numerous. We trained European honeybees (Apis mellifera) and European wasps (Vespula vulgaris) to select stimuli containing a higher quantity of yellow dots in arrays of blue and yellow dots and then presented them with the Solitaire Illusion. Insects learnt to discriminate between dot quantities and showed evidence of perceiving the Solitaire Illusion. Further work should determine whether the illusion is caused by numerical cues only or by both quantity and non-numerical spatial cues.

Blue Light Attracts More Spodoptera frugiperda Moths and Promotes Their Flight Speed

Light traps are a useful method for monitoring and controlling the important migratory pest, the fall armyworm, Spodoptera frugiperda. Studies have shown that S. frugiperda is sensitive to blue, green, or ultraviolet (UV) light, but the conclusions are inconsistent. Furthermore, conventional black light traps are less effective for trapping S. frugiperda. To improve the trapping efficiency of this pest, it is crucial to determine the specific wavelength to which S. frugiperda is sensitive and measure its flight capability under that wavelength. This study investigated the effects of light wavelength on the phototaxis and flight performance of S. frugiperda. The results showed that blue light was the most sensitive wavelength among the three different LED lights and was unaffected by gender. The flight capability of S. frugiperda varied significantly in different light conditions, especially for flight speed. The fastest flight speed was observed in blue light, whereas the slowest was observed in UV light compared to dark conditions. During a 12 h flight period, speed declined more rapidly in blue light and more slowly in UV, whereas speed remained stable in dark conditions. Meanwhile, the proportion of fast-flying individuals was highest under blue light, which was significantly higher than under UV light. Therefore, the use of light traps equipped with blue LED lights can improve the trapping efficiency of S. frugiperda. These results also provide insights for further research on the effects of light pollution on migratory insects.

Red vision in animals is broadly associated with lighting environment but not types of visual task

Red sensitivity is the exception rather than the norm in most animal groups. Among species with red sensitivity, there is substantial variation in the peak wavelength sensitivity (λmax) of the long wavelength sensitive (LWS) photoreceptor. It is unclear whether this variation can be explained by visual tuning to the light environment or to visual tasks such as signalling or foraging. Here, we examine long wavelength sensitivity across a broad range of taxa showing diversity in LWS photoreceptor λmax: insects, crustaceans, arachnids, amphibians, reptiles, fish, sharks and rays. We collated a list of 161 species with physiological evidence for a photoreceptor sensitive to red wavelengths (i.e. λmax ≥ 550 nm) and for each species documented abiotic and biotic factors that may be associated with peak sensitivity of the LWS photoreceptor. We found evidence supporting visual tuning to the light environment: terrestrial species had longer λmax than aquatic species, and of these, species from turbid shallow waters had longer λmax than those from clear or deep waters. Of the terrestrial species, diurnal species had longer λmax than nocturnal species, but we did not detect any differences across terrestrial habitats (closed, intermediate or open). We found no association with proxies for visual tasks such as having red morphological features or utilising flowers or coral reefs. These results support the emerging consensus that, in general, visual systems are broadly adapted to the lighting environment and diverse visual tasks. Links between visual systems and specific visual tasks are commonly reported, but these likely vary among species and do not lead to general patterns across species.

Flower colour and size-signals vary with altitude and resulting climate on the tropical-subtropical islands of Taiwan

The diversity of flower colours in nature provides quantifiable evidence for how visitations by colour sensing insect pollinators can drive the evolution of angiosperm visual signalling. Recent research shows that both biotic and abiotic factors may influence flower signalling, and that harsher climate conditions may also promote salient signalling to entice scarcer pollinators to visit. In parallel, a more sophisticated appreciation of the visual task foragers face reveals that bees have a complex visual system that uses achromatic vision when moving fast, whilst colour vision requires slower, more careful inspection of targets. Spectra of 714 native flowering species across Taiwan from sea level to mountainous regions 3,300 m above sea level (a.s.l.) were measured. We modelled how the visual system of key bee pollinators process signals, including flower size. By using phylogenetically informed analyses, we observed that at lower altitudes including foothills and submontane landscapes, there is a significant relationship between colour contrast and achromatic signals. Overall, the frequency of flowers with high colour contrast increases with altitude, whilst flower size decreases. The evidence that flower colour signaling becomes increasingly salient in higher altitude conditions supports that abiotic factors influence pollinator foraging in a way that directly influences how flowering plants need to advertise.

Ancient insect vision tuned for flight among rocks and plants underpins natural flower colour diversity

Understanding the origins of flower colour signalling to pollinators is fundamental to evolutionary biology and ecology. Flower colour evolves under pressure from visual systems of pollinators, like birds and insects, to establish global signatures among flowers with similar pollinators. However, an understanding of the ancient origins of this relationship remains elusive. Here, we employ computer simulations to generate artificial flower backgrounds assembled from real material sample spectra of rocks, leaves and dead plant materials, against which to test flowers' visibility to birds and bees. Our results indicate how flower colours differ from their backgrounds in strength, and the distributions of salient reflectance features when perceived by these key pollinators, to reveal the possible origins of their colours. Since Hymenopteran visual perception evolved before flowers, the terrestrial chromatic context for its evolution to facilitate flight and orientation consisted of rocks, leaves, sticks and bark. Flowers exploited these pre-evolved visual capacities of their visitors, in response evolving chromatic features to signal to bees, and differently to birds, against a backdrop of other natural materials. Consequently, it appears that today's flower colours may be an evolutionary response to the vision of diurnal pollinators navigating their world millennia prior to the first flowers.

Multiple axes of visual system diversity in Ithomiini, an ecologically diverse tribe of mimetic butterflies

The striking structural variation seen in arthropod visual systems can be explained by the overall quantity and spatio-temporal structure of light within habitats coupled with developmental and physiological constraints. However, little is currently known about how fine-scale variation in visual structures arises across shorter evolutionary and ecological scales. In this study, we characterise patterns of interspecific (between species), intraspecific (between sexes) and intraindividual (between eye regions) variation in the visual system of four ithomiine butterfly species. These species are part of a diverse 26-million-year-old Neotropical radiation where changes in mimetic colouration are associated with fine-scale shifts in ecology, such as microhabitat preference. Using a combination of selection analyses on visual opsin sequences, in vivo ophthalmoscopy, micro-computed tomography (micro-CT), immunohistochemistry, confocal microscopy and neural tracing, we quantify and describe physiological, anatomical and molecular traits involved in visual processing. Using these data, we provide evidence of substantial variation within the visual systems of Ithomiini, including: (i) relaxed selection on visual opsins, perhaps mediated by habitat preference, (ii) interspecific shifts in visual system physiology and anatomy, and (iii) extensive sexual dimorphism, including the complete absence of a butterfly-specific optic neuropil in the males of some species. We conclude that considerable visual system variation can exist within diverse insect radiations, hinting at the evolutionary lability of these systems to rapidly develop specialisations to distinct visual ecologies, with selection acting at the perceptual, processing and molecular level.

P-MIRU, a Polarized Multispectral Imaging System, Reveals Reflection Information on the Biological Surface

Reflection light forms the core of our visual perception of the world. We can obtain vast information by examining reflection light from biological surfaces, including pigment composition and distribution, tissue structure and surface microstructure. However, because of the limitations in our visual system, the complete information in reflection light, which we term 'reflectome', cannot be fully exploited. For example, we may miss reflection light information outside our visible wavelengths. In addition, unlike insects, we have virtually no sensitivity to light polarization. We can detect non-chromatic information lurking in reflection light only with appropriate devices. Although previous studies have designed and developed systems for specialized uses supporting our visual systems, we still do not have a versatile, rapid, convenient and affordable system for analyzing broad aspects of reflection from biological surfaces. To overcome this situation, we developed P-MIRU, a novel multispectral and polarization imaging system for reflecting light from biological surfaces. The hardware and software of P-MIRU are open source and customizable and thus can be applied for virtually any research on biological surfaces. Furthermore, P-MIRU is a user-friendly system for biologists with no specialized programming or engineering knowledge. P-MIRU successfully visualized multispectral reflection in visible/non-visible wavelengths and simultaneously detected various surface phenotypes of spectral polarization. The P-MIRU system extends our visual ability and unveils information on biological surfaces.

Molecular Evolution of Malacostracan Short Wavelength Sensitive Opsins

Investigations of the molecular mechanisms behind detection of short, and particularly ultraviolet, wavelengths in arthropods have relied heavily on studies from insects due to the relative ease of heterologous expression of modified opsin proteins in model organisms like Drosophila. However, species outside of the Insecta can provide information on mechanisms for spectral tuning as well as the evolutionary history of pancrustacean visual pigments. Here we investigate the basis of spectral tuning in malacostracan short wavelength sensitive (SWS) opsins using phylogenetic comparative methods. Tuning sites that may be responsible for the difference between ultraviolet (UV) and violet visual pigment absorbance in the Malacostraca are identified, and the idea that an amino acid polymorphism at a single site is responsible for this shift is shown to be unlikely. Instead, we suggest that this change in absorbance is accomplished through multiple amino acid substitutions. On the basis of our findings, we conducted further surveys to identify spectral tuning mechanisms in the order Stomatopoda where duplication of UV opsins has occurred. Ancestral state reconstructions of stomatopod opsins from two main clades provide insight into the amino acid changes that lead to differing absorption by the visual pigments they form, and likely contribute the basis for the wide array of UV spectral sensitivities found in this order.

Resistance of Common Bean Genotypes to Chrysodeixis includens (Walker, 1858) (Lepidoptera: Noctuidae)

The common bean (Phaseolus vulgaris L.) is an important leguminous crop providing low-cost protein in developing countries worldwide. Insect pests are the main threats to common bean production, and this article focuses on the soybean looper (SL) Chrysodeixis includens (Walker, 1858) (Lepidoptera: Noctuidae), which feeds on leaves and pods. The recurrent use of synthetic chemicals may lead to pest resistance. Genetically resistant plants may diminish their use. Thus, the objective was to study common bean genotypes' resistance toward SL. The plants were grown in greenhouse conditions. The biology, fertility life table, oviposition preference and free-choice feeding preference were analyzed. Phenol and flavonoid content were assessed in leaves using a biology assay. Uirapuru genotype negatively affected C. includens biology and reproduction. Tangará genotype favored these parameters. Genotypes Quero-Quero, Nhambu, Corujinha, Andorinha, ANFC 9, Siriri, BRS Radiante and Verdão were more attractive for third-instar larvae. Negative correlations between phenolic and flavonoid compounds with survival rate (from egg to adult) rate were found. Common bean genotypes with dark leaves are less preferred for oviposition.

Ontogeny of color development in two green-brown polymorphic grasshopper species

Many insects, including several orthopterans, undergo dramatic changes in body coloration during ontogeny. This variation is particularly intriguing in gomphocerine grasshoppers, where the green and brown morphs appear to be genetically determined (Schielzeth & Dieker, 2020, BMC Evolutionary Biology, 20, 63; Winter et al., 2021, Heredity, 127, 66). A better understanding of how these color morphs develop during ontogeny can provide valuable insights into the evolution and ecology of such a widespread color polymorphism. Here, we focus on the color development of two green-brown polymorphic species, the club-legged grasshopper Gomphocerus sibiricus and the steppe grasshopper Chorthippus dorsatus. By following the color development of individuals from hatching to adulthood, we found that color morph differences begin to develop during the second nymphal stage, are clearly defined by the third nymphal stage, and remain stable throughout the life of an individual. Interestingly, we also observed that shed skins of late nymphal stages are identifiable by color morphs based on their yellowish coloration, rather than the green that marks green body parts. Furthermore, by assessing how these colors are perceived by different visual systems, we found that certain potential predators can chromatically discriminate between morphs, while others may not. These results suggest that the putative genes controlling color morph are active during the early stages of ontogeny, and that green color is likely composed of two components, one present in the cuticle and one not. In addition, the effectiveness of camouflage appears to vary depending on the specific predator involved.

Expression and function of opsin genes associated with phototaxis in Zeugodacus cucurbitae Coquillett (Diptera: Tephritidae)

BACKGROUND

Zeugodacus cucuribitae is a major agricultural pest that causes significant damage to varieties of plants. Vision plays a critical role in phototactic behavior of herbivorous insects. However, the effect of opsin on the phototactic behavior in Z. cucuribitae remains unknown. The aim of this research is to explore the key opsin genes that associate with phototaxis behavior of Z. cucurbitae.

RESULTS

Five opsin genes were identified and their expression patterns were analyzed. The relative expression levels of ZcRh1, ZcRh4 and ZcRh6 were highest in 4-day-old larvae, ZcRh2 and ZcRh3 were highest in 3rd-instar larvae and 5-day-old pupae, respectively. Furthermore, five opsin genes had the highest expression levels in compound eyes, followed by the antennae and head, whereas the lower occurred in other tissues. The expression of the long-wavelength-sensitive (LW) opsins first decreased and then increased under green light exposure. In contrast, the expression of ultraviolet-sensitive (UV) opsins first increased and then decreased with the duration of UV exposure. Silencing of LW opsin (dsZcRh1, dsZcRh2, and dsZcRh6) and UV opsin (dsZcRh3 and dsZcRh4) reduced the phototactic efficiency of Z. cucurbitae to green light by 52.27%, 60.72%, and 67.89%, and to UV light by 68.59% and 61.73%, respectively.

CONCLUSION

The results indicate that RNAi inhibited the expression of opsin, thereby inhibiting the phototaxis of Z. cucurbitae. This result provides theoretical support for the physical control of Z. cucurbitae and lays the foundation for further exploration of the mechanism of insect phototaxis. © 2023 Society of Chemical Industry.

Adaptation to pollination by fungus gnats underlies the evolution of pollination syndrome in the genus Euonymus

BACKGROUND AND AIMS

Dipteran insects are known pollinators of many angiosperms, but knowledge on how flies affect floral evolution is relatively scarce. Some plants pollinated by fungus gnats share a unique set of floral characters (dark red display, flat shape and short stamens), which differs from any known pollination syndromes. We tested whether this set of floral characters is a pollination syndrome associated with pollination by fungus gnats, using the genus Euonymus as a model.

METHODS

The pollinator and floral colour, morphology and scent profile were investigated for ten Euonymus species and Tripterygium regelii as an outgroup. The flower colour was evaluated using bee and fly colour vision models. The evolutionary association between fungus gnat pollination and each plant character was tested using a phylogenetically independent contrast. The ancestral state reconstruction was performed on flower colour, which is associated with fungus gnat pollination, to infer the evolution of pollination in the genus Euonymus.

KEY RESULTS

The red-flowered Euonymus species were pollinated predominantly by fungus gnats, whereas the white-flowered species were pollinated by bees, beetles and brachyceran flies. The colour vision analysis suggested that red and white flowers are perceived as different colours by both bees and flies. The floral scents of the fungus gnat-pollinated species were characterized by acetoin, which made up >90 % of the total scent in three species. Phylogenetically independent contrast showed that the evolution of fungus gnat pollination is associated with acquisition of red flowers, short stamens and acetoin emission.

CONCLUSIONS

Our results suggest that the observed combination of floral characters is a pollination syndrome associated with the parallel evolution of pollination by fungus gnats. Although the role of the red floral display and acetoin in pollinator attraction remains to be elucidated, our finding underscores the importance of fungus gnats as potential contributors to floral diversification.

Parallel Losses of Blue Opsin Correlate with Compensatory Neofunctionalization of UV-Opsin Gene Duplicates in Aphids and Planthoppers

Expanding on previous efforts to survey the visual opsin repertoires of the Hemiptera, this study confirms that homologs of the UV- and LW-opsin subfamilies are conserved in all Hemiptera, while the B-opsin subfamily is missing from the Heteroptera and subgroups of the Sternorrhyncha and Auchenorrhyncha, i.e., aphids (Aphidoidea) and planthoppers (Fulgoroidea), respectively. Unlike in the Heteroptera, which are characterized by multiple independent expansions of the LW-opsin subfamily, the lack of B-opsin correlates with the presence of tandem-duplicated UV-opsins in aphids and planthoppers. Available data on organismal wavelength sensitivities and retinal gene expression patterns lead to the conclusion that, in both groups, one UV-opsin paralog shifted from ancestral UV peak sensitivity to derived blue sensitivity, likely compensating for the lost B-opsin. Two parallel bona fide tuning site substitutions compare to 18 non-corresponding amino acid replacements in the blue-shifted UV-opsin paralogs of aphids and planthoppers. Most notably, while the aphid blue-shifted UV-opsin clade is characterized by a replacement substitution at one of the best-documented UV/blue tuning sites (Rhodopsin site 90), the planthopper blue-shifted UV-opsin paralogs retained the ancestral lysine at this position. Combined, the new findings identify aphid and planthopper UV-opsins as a new valuable data sample for studying adaptive opsin evolution.

Evaluation of the solar-powered Silver Bullet 2.1 (Lumin 8) light trap for sampling malaria vectors in western Kenya

BACKGROUND

Centers for Disease Control and Prevention (CDC) light traps are widely used for sampling mosquitoes. However, this trap, manufactured in the USA, poses challenges for use in sub-Saharan Africa due to procurement costs and shipping time. Traps that are equally efficient than the CDC light trap, but which are amenable for use in remote African settings and made in Africa, are desirable to improve local vector surveillance. This study evaluated a novel solar-powered light trap made in South Africa (Silver Bullet trap; SB), for its efficiency in malaria vector sampling in western Kenya.

METHODS

Large cage (173.7 m3) experiments and field evaluations were conducted to compare the CDC-incandescent light trap (CDC-iLT), CDC-UV fluorescent tube light trap (CDC-UV), SB with white diodes (SB-White) and SB with UV diodes (SB-UV) for sampling Anopheles mosquitoes. Field assessments were done indoors and outdoors following a Latin square design. The wavelengths and absolute spectral irradiance of traps were compared using spectrometry.

RESULTS

The odds of catching a released Anopheles in the large cage experiments with the SB-UV under ambient conditions in the presence of a CDC-iLT in the same system was three times higher than what would have been expected when the two traps were equally attractive (odds ratio (OR) 3.2, 95% confidence interval CI 2.8-3.7, P < 0.01)). However, when the white light diode was used in the SB trap, it could not compete with the CDC-iLT (OR 0.56, 95% CI 0.48-0.66, p < 0.01) when the two traps were provided as choices in a closed system. In the field, the CDC and Silver Bullet traps were equally effective in mosquito sampling. Irrespective of manufacturer, traps emitting UV light performed better than white or incandescent light for indoor sampling, collecting two times more Anopheles funestus sensu lato (s.l.) (RR 2.5; 95% CI 1.7-3.8) and Anopheles gambiae s.l. (RR 2.5; 95% 1.7-3.6). Outdoor collections were lower than indoor collections and similar for all light sources and traps.

CONCLUSIONS

The solar-powered SB trap compared well with the CDC trap in the field and presents a promising new surveillance device especially when charging on mains electricity is challenging in remote settings.

The morphology and spectral characteristics of the compound eye of Agasicleshygrophila (Selman & Vogt, 1971) (Coleoptera, Chrysomelidae, Galerucinae, Alticini)

The first exploratory study was conducted on the compound eye morphology and spectral characteristics of Agasicleshygrophila (Selman & Vogt, 1971) to clarify its eye structure and its spectral sensitivity. Scanning electron microscopy, paraffin sectioning, and transmission electron microscopy revealed that A.hygrophila has apposition compound eyes with both eucones and open rhabdom. The micro-computed tomography (CT) results after 3D reconstruction demonstrated the precise position of the compound eyes in the insect's head and suggested that the visual range was mainly concentrated in the front and on both sides of the head. The electroretinogram (ERG) experiment showed that red, yellow, green, blue, and ultraviolet light could stimulate the compound eyes of A.hygrophila to produce electrical signals. The behavioural experiment results showed that both males and females had the strongest phototaxis to yellow light and positive phototaxis to red, green, and blue light but negative phototaxis to UV light. This study of the compound eyes of A.hygrophila will be helpful for decoding its visual mechanism in future studies.

Dim-light colour vision in the facultatively nocturnal Asian giant honeybee, Apis dorsata

We discovered nocturnal colour vision in the Asian giant honeybee Apis dorsata-a facultatively nocturnal species-at mesopic light intensities, down to half-moon light levels (approx. 10-2 cd m-2). The visual threshold of nocturnality aligns with their reported nocturnal activity down to the same light levels. Nocturnal colour vision in A. dorsata is interesting because, despite being primarily diurnal, its colour vision capabilities extend into dim light, while the 'model' European honeybee Apis mellifera is reported to be colour-blind at twilight. By employing behavioural experiments with naturally nesting A. dorsata colonies, we show discrimination of the trained colour from other stimuli during the day, and significantly, even at night. Nocturnal colour vision in bees has so far only been reported in the obligately nocturnal carpenter bee Xylocopa tranquebarica. The discovery of colour vision in these two bee species, despite differences in the extent of their nocturnality and the limitations of their apposition compound eye optics, opens avenues for future studies on visual adaptations for dim-light colour vision, their role in pollination of flowers at night, and the effect of light pollution on nocturnal activity in A. dorsata, a ubiquitous pollinator in natural, agricultural and urban habitats in the Asian tropics and sub-tropics.

CYCLOIDEA-like genes control floral symmetry, floral orientation, and nectar guide patterning

Actinomorphic flowers usually orient vertically (relative to the horizon) and possess symmetric nectar guides, while zygomorphic flowers often face horizontally and have asymmetric nectar guides, indicating that floral symmetry, floral orientation, and nectar guide patterning are correlated. The origin of floral zygomorphy is dependent on the dorsoventrally asymmetric expression of CYCLOIDEA (CYC)-like genes. However, how horizontal orientation and asymmetric nectar guides are achieved remains poorly understood. Here, we selected Chirita pumila (Gesneriaceae) as a model plant to explore the molecular bases for these traits. By analyzing gene expression patterns, protein-DNA and protein-protein interactions, and encoded protein functions, we identified multiple roles and functional divergence of 2 CYC-like genes, i.e. CpCYC1 and CpCYC2, in controlling floral symmetry, floral orientation, and nectar guide patterning. CpCYC1 positively regulates its own expression, whereas CpCYC2 does not regulate itself. In addition, CpCYC2 upregulates CpCYC1, while CpCYC1 downregulates CpCYC2. This asymmetric auto-regulation and cross-regulation mechanism might explain the high expression levels of only 1 of these genes. We show that CpCYC1 and CpCYC2 determine asymmetric nectar guide formation, likely by directly repressing the flavonoid synthesis-related gene CpF3'5'H. We further suggest that CYC-like genes play multiple conserved roles in Gesneriaceae. These findings shed light on the repeated origins of zygomorphic flowers in angiosperms.

Oviposition behavior is not affected by ultraviolet light in a butterfly with sexually-dimorphic expression of a UV-sensitive opsin

Animal vision is important for mediating multiple complex behaviors. In Heliconius butterflies, vision guides fundamental behaviors such as oviposition, foraging, and mate choice. Color vision in Heliconius involves ultraviolet (UV), blue and long-wavelength-sensitive photoreceptors (opsins). Additionally, Heliconius possess a duplicated UV opsin, and its expression varies widely within the genus. In Heliconius erato, opsin expression is sexually dimorphic; only females express both UV-sensitive opsins, enabling UV wavelength discrimination. However, the selective pressures responsible for sex-specific differences in opsin expression and visual perception remain unresolved. Female Heliconius invest heavily in finding suitable hostplants for oviposition, a behavior heavily dependent on visual cues. Here, we tested the hypothesis that UV vision is important for oviposition in H. erato and Heliconius himera females by manipulating the availability of UV in behavioral experiments under natural conditions. Our results indicate that UV does not influence the number of oviposition attempts or eggs laid, and the hostplant, Passiflora punctata, does not reflect UV wavelengths. Models of H. erato female vision suggest only minimal stimulation of the UV opsins. Overall, these findings suggest that UV wavelengths do not directly affect the ability of Heliconius females to find suitable oviposition sites. Alternatively, UV discrimination could be used in the context of foraging or mate choice, but this remains to be tested.

Long-wave opsin involved in body color plastic development in Nilaparvata lugens

BACKGROUND

As one of the components of visual photopigments in photoreceptor cells, opsin exhibits different spectral peaks and plays crucial roles in visual function. Besides, it is discovered to evolve other functions despite color vision. However, research on its unconventional function is limited nowadays. With the increase in genome database numbers, various numbers and types of opsins have been identified in insects due to gene duplications or losses. The Nilaparvata lugens (Hemiptera) is a rice pest known for its long-distance migration capability. In this study, opsins were identified in N. lugens and characterized by genome and transcriptome analyses. Meanwhile, RNA interference (RNAi) was carried out to investigate the functions of opsins, and then the Illumina Novaseq 6000 platform-based transcriptome sequencing was performed to reveal gene expression patterns.

RESULTS

Four opsins belonging to G protein-coupled receptors were identified in the N. lugens genome, including one long-sensitive opsin (Nllw) together with two ultraviolet-sensitive opsins (NlUV1/2) and an additional new opsin with hypothesized UV peak sensitivity (NlUV3-like). A tandem array of NlUV1/2 on the chromosome suggested the presence of a gene duplication event, with similar exons distribution. Moreover, as revealed by spatiotemporal expression, the four opsins were highly expressed in eyes with age-different expression levels. Besides, RNAi targeting each of the four opsins did not significantly affect the survival of N. lugens in phytotron, but the silencing of Nllw resulted in the melanization of body color. Further transcriptome analysis revealed that silencing of Nllw resulted in up-regulation of a tyrosine hydroxylase gene (NlTH) and down-regulation of an arylalkylamine-N-acetyltransferases gene (NlaaNAT) in N. lugens, demonstrating that Nllw is involved in body color plastic development via the tyrosine-mediated melanism pathway.

CONCLUSIONS

This study provides the first evidence in a Hemipteran insect that an opsin (Nllw) takes part in the regulation of cuticle melanization, confirming a cross-talk between the gene pathways underlying the visual system and the morphological differentiation in insects.

Discovering Aethina tumida responses to attractant and repellent molecules: A potential basis for future management strategies

Small hive beetle (Aethina tumida) management has been highly dependent upon chemical and mechanical control over the past two decades; however, many of these methods have not been consistently effective or safe for European honey bee (Apis mellifera) colonies. Here we explore the behavioral and physiological effects of the attractants isopentyl acetate and pollen patty upon A. tumida adults, and also investigate the mixture of attractants with repellent compounds, which were previously untested against A. tumida. Electroantennograms established sensitivity of A. tumida antennae to both attractants and all repellents with the exception of DEET, with antennae displaying greatest sensitivity to the repellent pyrrolidine. A walking-response olfactometer, designed specifically for A. tumida, was used for all behavioral experiments. It was found that both pollen patty and isopentyl acetate were attractive to A. tumida adults; conversely, mixes of attractants and repellent volatiles led to less attraction or avoidance of what was previously a significantly attractive source. Of all repellents tested, pyrrolidine was found to be the most repelling molecule, with significant avoidance of the attractive source at a 10 mg treatment of pyrrolidine. The results of this study indicate that, at the behavioral level, the repellent compounds pyrrolidine and 1,4-dimethylpiperazine resulted in a negative preference index indicating a repellent behavioral response. By strategically implementing a repellent source in an apiary environment, A. tumida adults could be deterred from entering and invading hives.

Microlia cayaponia, a new pollen-feeder species from Brazil (Staphylinidae: Aleocharinae: Hoplandriini) and its potential competitionin pollinator activity in Cayaponia plants (Cucurbitaceae)

Microlia Casey is a genus of small rove beetles from the New World and Australasia. Many species are recorded to be associated with the flowers of Cucurbitaceae, Solanaceae, Asteraceae, and Monimiaceae. In this work, a new species from Brazil associated with flowers of Cayaponia (Cucurbitaceae), Microlia cayaponia Zilberman & Pires-Silva sp. nov., is described and illustrated. Aspects of its natural history are also investigated, with insights on foraging, reproduction, and the supposed impact on the plant and pollinator's fitness.

Effect of ultraviolet LED and trap height on catches of host-seeking anopheline mosquitoes by using a low-cost passive light trap in northeast Brazil

Light traps have been widely used for monitoring malaria vectors, although drawbacks remain. In this context, new tools and attractants are always becoming available to perform monitoring tasks, like the Silva trap, a passive and low-cost LED-light trap for host-seeking anopheline mosquitoes. In this work, the effectiveness of the Silva trap by using UV-LED and at different heights as well as a comparison with the conventional CDC-type (HP) light trap was studied. A total of 9009 mosquitoes and nine species were caught, Anopheles triannulatus, An. argyritarsis, and An. goeldii being the most frequent species. The green (520 nm) and blue (470 nm) LEDs attracted almost equal numbers of anopheline mosquitoes, but UV LEDs (395 nm) attracted a significantly lower number of individuals (Kruskal-Wallis = 19.68, P = 0.0001). Even with the predominance of mosquitoes trapped at the height of 1.5 m, no significant statistical difference was found among the four heights tested (0.5 m; 1.0 m; 1.5 m; 2.0 m). Green-baited Silva traps collected significantly more individuals than incandescent-baited CDC-type traps (U = 60.5; P = 0.0303). LEDs have been useful as light sources for attracting insect vectors and together with a low-cost trap, as the Silva trap, a feasible alternative to conventional trap-based monitoring Anopheles mosquitoes that can be implemented in the field.

The Contribution of Singletons and Doubletons Captured Using Weak Light Heath Traps for the Analysis of the Macroheteroceran Assemblages in Forest Biotopes

In nearly every ecological community, most species are represented by a few individuals, and most individuals come from a few of the most common species. Singletons (one individual sampled) and doubletons (two individuals sampled) are very common in moth community studies. In some reports, these specimens are excluded from the analysis once they are considered a consequence of under-sampling or of contamination with tourist species that are just passing through. Throughout 12 nights in 2018 and 12 nights in 2019, two Heath traps, one with an 8 W ultraviolet lamp and the other with a 15 W actinic lamp, were positioned approximately 50 m apart at nine sites of four different biotopes in a mosaic forest ecosystem in the Narew National Park (NE Poland). We were able to differentiate moth assemblages according to the forest biotopes under study and by the year of research. With our results, it becomes more evident that singletons and doubletons sampled using weak light Heath traps should be included in the ecological analysis of Macroheteroceran moth assemblages, and our research strongly suggests that they are an important and consistent element of such a sampling method. We also demonstrate that weak light Heath traps are suitable for building an inventory scheme of moth assemblages in small forest areas and that singletons and doubletons can be crucial elements in long-term monitoring systems.

Information Optimization and Transferable State Abstractions in Deep Reinforcement Learning

While humans and animals learn incrementally during their lifetimes and exploit their experience to solve new tasks, standard deep reinforcement learning methods specialize to solve only one task at a time. As a result, the information they acquire is hardly reusable in new situations. Here, we introduce a new perspective on the problem of leveraging prior knowledge to solve future tasks. We show that learning discrete representations of sensory inputs can provide a high-level abstraction that is common across multiple tasks, thus facilitating the transference of information. In particular, we show that it is possible to learn such representations by self-supervision, following an information theoretic approach. Our method is able to learn abstractions in locomotive and optimal control tasks that increase the sample efficiency in both known and unknown tasks, opening a new path to endow artificial agents with generalization abilities.

A Review of the Host Plant Location and Recognition Mechanisms of Asian Longhorn Beetle

The Asian longhorn beetle (ALB), Anoplophora glabripennis Motschulsky, is a polyphagous xylophage with dozens of reported host tree species. However, the mechanisms by which individuals locate and recognize host plants are still unknown. We summarize the current knowledge of the host plant list, host kairomones, odorant-binding proteins (OBPs) and microbial symbionts of this beetle and their practical applications, and finally discuss the host localization and recognition mechanisms. A total of 209 species (or cultivars) were reported as ALB host plants, including 101 species of higher sensitivity; host kairomones were preferentially bound to ALB recombinant OBPs, including cis-3-hexen-1-ol, δ-3-carene, nonanal, linalool, and β-caryophyllene. In addition, microbial symbionts may help ALB degrade their host. Complementarity of tree species with different levels of resistance may reduce damage, but trapping effectiveness for adults was limited using a combination of host kairomones and sex pheromones in the field. Therefore, we discuss host location behavior from a new perspective and show that multiple cues are used by ALB to locate and recognize host plants. Further research into host resistance mechanisms and visual signal recognition, and the interaction of sex pheromone synthesis, symbiont microbiota, and host plants may help reveal the host recognition mechanisms of ALBs.

Insect exuviae as soil amendment affect flower reflectance and increase flower production and plant volatile emission

Soil composition and herbivory are two environmental factors that can affect plant traits including flower traits, thus potentially affecting plant-pollinator interactions. Importantly, soil composition and herbivory may interact in these effects, with consequences for plant fitness. We assessed the main effects of aboveground insect herbivory and soil amendment with exuviae of three different insect species on visual and olfactory traits of Brassica nigra plants, including interactive effects. We combined various methodological approaches including gas chromatography/mass spectrometry, spectroscopy and machine learning to evaluate changes in flower morphology, colour and the emission of volatile organic compounds (VOCs). Soil amended with insect exuviae increased the total number of flowers per plant and VOC emission, whereas herbivory reduced petal area and VOC emission. Soil amendment and herbivory interacted in their effect on the floral reflectance spectrum of the base part of petals and the emission of 10 VOCs. These findings demonstrate the effects of insect exuviae as soil amendment on plant traits involved in reproduction, with a potential for enhanced reproductive success by increasing the strength of signals attracting pollinators and by mitigating the negative effects of herbivory.

Linear scaling – negative effects of invasive Spiraea tomentosa (Rosaceae) on wetland plants and pollinator communities

Invasive plants directly and indirectly disrupt the ecosystem functioning, of which indirect effects, for example, through trophic cascades, are particularly difficult to predict. It is frequently assumed that the impact of an invading species on the ecosystem is proportional (linearly related) to its density or abundance in a habitat, but this assumption has rarely been tested. We hypothesised that abundance and richness of plants and potentially pollinators of wet meadows change as a result of invasion of steeplebush Spiraea tomentosa and that these changes are proportional to the density of the shrub. We selected 27 sites amongst wet meadows habitats invaded by S. tomentosa with coverage ranging from 0% to 100% and examined the diversity of plants, as well as the abundance and diversity of flower visitors (bees, butterflies with moths and flies). Our results showed that the richness of plants, as well as the richness and number of individuals of flower visitors, decrease significantly and linearly with an increase of the S. tomentosa cover. This finding supports the hypothesis that the impact of an invasive species can be proportional to their population density, especially if this species is limiting the available resources without supplying others. Our study is the first to show such an unequivocal negative, linear effect of an invasive shrub on the abundance and richness of potential pollinators. It proves that the negative impact of S. tomentosa on the wetland ecosystem appears even with a minor coverage of the invader, which should be taken into account when planning activities aimed at controlling the population of this transformer species. The simultaneously detected linear dependence allows us to assume that the benefits of controlling secondary populations of the shrub can be proportional to the incurred effort.

Mimicking orchids lure bees from afar with exaggerated ultraviolet signals

Flowers have many traits to appeal to pollinators, including ultraviolet (UV) absorbing markings, which are well-known for attracting bees at close proximity (e.g., <1 m). While striking UV signals have been thought to attract pollinators also from far away, if these signals impact the plant pollinia removal over distance remains unknown. Here, we report the case of the Australian orchid Diuris brumalis, a nonrewarding species, pollinated by bees via mimicry of the rewarding pea plant Daviesia decurrens. When distant from the pea plant, Diuris was hypothesized to enhance pollinator attraction by exaggeratedly mimicking the floral ultraviolet (UV) reflecting patterns of its model. By experimentally modulating floral UV reflectance with a UV screening solution, we quantified the orchid pollinia removal at a variable distance from the model pea plants. We demonstrate that the deceptive orchid Diuris attracts bee pollinators by emphasizing the visual stimuli, which mimic the floral UV signaling of the rewarding model Daviesia. Moreover, the exaggerated UV reflectance of Diuris flowers impacted pollinators' visitation at an optimal distance from Da. decurrens, and the effect decreased when orchids were too close or too far away from the model. Our findings support the hypothesis that salient UV flower signaling plays a functional role in visual floral mimicry, likely exploiting perceptual gaps in bee neural coding, and mediates the plant pollinia removal at much greater spatial scales than previously expected. The ruse works most effectively at an optimal distance of several meters revealing the importance of salient visual stimuli when mimicry is imperfect.

Spectral sensitivities of the orchid bee Euglossa dilemma

Diurnal pollinators often rely on color cues to make decisions when visiting flowers. Orchid bees are major tropical pollinators, with most studies of their pollination behavior to date focusing on scent collection and chemical ecology. The objective of this study was to measure their spectral sensitivities to preliminarily characterize color vision in the orchid bee Euglossa dilemma and compare it to the known spectral sensitivity of other closely related bees. We compared E. dilemma's spectral sensitivities and opsin protein sequences to four closely related corbiculate bees. E. dilemma appears to have trichromatic vision, with spectral sensitivity peaks in the ultraviolet, blue, and green wavelengths (347 ± 0.957 (SE) nm, 429 ± 6.570 nm, and 537 ± 1.183 nm, respectively), similar to other measured bees. We found no differences between male and female E. dilemma visual systems despite neuroanatomical and behavioral differences reported in the literature. The lambda maxes of the ultraviolet-sensitive photoreceptors appeared to be the most conserved among the bees we compared. Meanwhile, both the lambda maxes of the blue photoreceptors and the blue opsin proteins sequences were the least conserved. Our results open up new possibilities for the study of color vision and color-mediated pollination behaviors in orchid bees.

Intrafloral patterns of color and scent in Capparis spinosa L. and the ghosts of its selection past

PREMISE

Capparis spinosa is a widespread charismatic plant, in which the nocturnal floral habit contrasts with the high visitation by diurnal bees and the pronounced scarcity of hawkmoths. To resolve this discrepancy and elucidate floral evolution of C. spinosa, we analyzed the intrafloral patterns of visual and olfactory cues in relation to the known sensory biases of the different visitor guilds (bees, butterflies, and hawkmoths).

METHODS

We measured the intrafloral variation of scent, reflectance spectra, and colorimetric properties according to three guilds of known visitors of C. spinosa. Additionally, we sampled visitation rates using a motion-activated camera.

RESULTS

Carpenter bees visited the flowers eight times more frequently than nocturnal hawkmoths, at dusk and in the following morning. Yet, the floral headspace of C. spinosa contained a typical sphingophilous scent with high emission rates of certain monoterpenes and amino-acid derived compounds. Visual cues included a special case of multisensory nectar guide and color patterns conspicuous to the visual systems of both hawkmoths and bees.

CONCLUSIONS

The intrafloral patterns of sensory stimuli suggest that hawkmoths have exerted strong historical selection on C. spinosa. Our study revealed two interesting paradoxes: (a) the flowers phenotypically biased towards the more inconsistent pollinator; and (b) floral display demands an abundance of resources that seems maladaptive in the habitats of C. spinosa. The transition to a binary pollination system accommodating large bees has not required phenotypic changes, owing to specific eco-physiological adaptations, unrelated to pollination, which make this plant an unusual case in pollination ecology.

Electrophysiological detection of visible wavelengths of artificial lights inducing take-off in adults of Rhodnius prolixus (Hemiptera: Triatominae)

Rhodnius prolixus is the most important vector of Trypanosoma cruzi in the northern part of South America. The compound eyes in adults of R. prolixus are involved in the nocturnal flight dispersion from sylvatic environments into human dwellings. During this behavior, the artificial lights play an important role in attracting R. prolixus; however, it is still not clear whether the compound eyes of this species use different visible wavelengths as a cue during active dispersion. We applied electrophysiological (electroretinography or ERG) and behavioral (take-off) experiments in a controlled laboratory setting to determine the spectral sensitivity of the compound eyes and the attraction of R. prolixus adults to discrete visible wavelengths. For the ERG experiments, flashes of 300 ms at wavelengths ranging between 350 and 700 nm at a constant intensity of 3.4 µW/cm2 were tested after adaptation to darkness and to blue and yellow lights. For the behavioral experiments, the adults were exposed to nine visible wavelengths at three different intensities, and their direction of take-off in an experimental arena was established with circular statistics. The ERG results showed peaks of spectral sensitivity at 470-490 nm and 520-550 nm in adults, while behavioral experiments showed attractions to blue, green and red lights, depending on the intensity of the light stimuli. The electrophysiological and behavioral results confirm that R. prolixus adults can detect certain wavelengths in the visible spectrum of light and be attracted to them during take-off.

Single gene mutation in a plant MYB transcription factor causes a major shift in pollinator preference

Understanding the molecular basis of reproductive isolation and speciation is a key goal of evolutionary genetics. In the South American genus Petunia, the R2R3-MYB transcription factor MYB-FL regulates the biosynthesis of UV-absorbing flavonol pigments, a major determinant of pollinator preference. MYB-FL is highly expressed in the hawkmoth-pollinated P. axillaris, but independent losses of its activity in sister taxa P. secreta and P. exserta led to UV-reflective flowers and associated pollinator shifts in each lineage (bees and hummingbirds, respectively). We created a myb-fl CRISPR mutant in P. axillaris and studied the effect of this single gene on innate pollinator preference. The mutation strongly reduced the expression of the two key flavonol-related biosynthetic genes but only affected the expression of few other genes. The mutant flowers were UV reflective as expected but additionally contained low levels of visible anthocyanin pigments. Hawkmoths strongly preferred the wild-type P. axillaris over the myb-fl mutant, whereas both social and solitary bee preference depended on the level of visible color of the mutants. MYB-FL, with its specific expression pattern, small number of target genes, and key position at the nexus of flavonol and anthocyanin biosynthetic pathways, provides a striking example of evolution by single mutations of large phenotypic effect.

Attraction of Insects to Ornamental Lighting Used on Cultural Heritage Buildings: A Case Study in an Urban Area

Artificial light at night (ALAN) reduces insect populations by altering their movements, foraging, reproduction, and predation. Although ALAN is mainly associated with streetlights and road networks, the ornamental illumination of monuments is making an increasing (but not well-studied) contribution. We compared insect attraction to two different types of light sources: a metal halide lamp (a type currently used to illuminate monuments) and an environmentally sound prototype lamp (CromaLux) comprising a combination of green and amber LEDs. The experiment was performed within the pilot CromaLux project in Santiago de Compostela (NW Spain). The abundance and diversity of the insects captured between June and October 2021 in the areas surrounding both light sources and in an unlit area were compared. By limiting the light emitted to amber and green, the CromaLux lamps reduced the number and diversity of insects, morphospecies, and orders attracted to the light, with similar numbers captured as in the unilluminated area, while a greater diversity of insects was captured beside the metal halide lamp. This effect has been demonstrated for almost all insect orders trapped, especially in Diptera, Lepidoptera, Coleoptera, Hemiptera, and Hymenoptera. On the contrary, Psocoptera showed a similar attraction to the CromaLux and metal halide lamps, a phenomenon whose causes deserve further investigation. As expected, Diptera were the most diverse and abundant insects in all samples, but the abundance of Lepidoptera was unexpectedly low (4%), which is in line with the worldwide evidence of the progressive decline of populations of this group. The study findings provide evidence that selecting specific wavelengths for ornamental lighting reduces the attraction of insects while maintaining adequate illumination of monuments for aesthetic purposes, resulting in a lower environmental impact on nocturnal insects. This study provides reference data for developing principles of good practices leading to possible regulatory and legal solutions and the incorporation of specific measures for artificial lighting of monuments and urban structures.