The transfer of male cuticular hydrocarbons provides a reliable cue of the risk and intensity of sperm competition in decorated crickets.

Theoretically, males should increase their ejaculate expenditure when the probability of sperm competition occurring (or risk) is high but decrease ejaculate expenditure as the number of competing ejaculates (or intensity) increases. Here we examine whether male decorated crickets (Gryllodes sigillatus) use cuticular hydrocarbons (CHCs) transferred to females by rival males at mating to assess the risk and intensity of sperm competition and adjust their ejaculate accordingly. Unmated females and those perfumed with CHCs extracted from one, three or five males could be distinguished chemically, providing a reliable cue of the risk and intensity of sperm competition. In agreement with theory, males mating with these females increased sperm number with the risk of sperm competition and decreased sperm number with the intensity of sperm competition. Similarly, as the risk of sperm competition increased, males produced a larger and more attractive spermatophylax (an important non-sperm component of the ejaculate) but these traits did not vary with the intensity of sperm competition. Our results therefore demonstrate that both sperm and non-sperm components of the male ejaculate respond to the risk and intensity of sperm competition in different ways and that CHCs provide males with an important cue to strategically tailor their ejaculate.

Genomic basis of adaptation to climate and parasite prevalence and the importance of odorant perception in the ant Temnothorax longispinosus.

A co-evolutionary arms race ensues when parasites exhibit exploitative behaviour, which prompts adaptations in their hosts, in turn triggering counter-adaptations by the parasites. To unravel the genomic basis of this coevolution from the host's perspective, we collected ants of the host species Temnothorax longispinosus, parasitized by the social parasite Temnothorax americanus, from 10 populations in the northeastern United States exhibiting varying levels of parasite prevalence and living under different climatic conditions. We conducted a genome-wide association study (GWAS) to identify single nucleotide polymorphisms (SNPs) associated with both prevalence and climate. Our investigation highlighted a multitude of candidate SNPs associated with parasite prevalence, particularly in genes responsible for sensory perception of smell including odorant receptor genes. We further focused on population-specific compositions of cuticular hydrocarbons, a complex trait important for signalling, communication and protection against desiccation. The relative abundances of n-alkanes were correlated with climate, while there was only a trend between parasite prevalence and the relative abundances of known recognition cues. Furthermore, we identified candidate genes likely involved in the synthesis and recognition of specific hydrocarbons. In addition, we analysed the population-level gene expression in the antennae, the primary organ for odorant reception, and established a strong correlation with parasite prevalence. Our comprehensive study highlights the intricate genomic patterns forged by the interplay of diverse selection factors and how these are manifested in the expression of various phenotypes.

Genetic Underpinnings of Cuticular Hydrocarbon Biosynthesis in the German Cockroach, Blattella germanica (L.): Progress and Perspectives.

Insect cuticular hydrocarbons (CHCs) serve as important waterproofing barriers and as signals and cues in chemical communication. Over the past 30 years, numerous studies on CHCs have been conducted in the German cockroach, Blattella germanica, leading to substantial progress in the field. However, there has not been a systematic review of CHC studies in this species in recent years. This review aims to provide a concise overview of the chemical composition, storage, transport, and physical properties of different CHCs in B. germanica. Additionally, we focus on the biosynthetic pathway and the genetic regulation of HC biosynthesis in this species. A considerable amount of biochemical evidence regarding the biosynthetic pathway of insect CHCs has been gathered from studies conducted in B. germanica. In recent years, there has also been an improved understanding of the molecular mechanisms that underlie CHC production in this insect. In this article, we summarize the biosynthesis of different classes of CHCs in B. germanica. Then, we review CHCs reaction to various environmental conditions and stressors and internal physiological states. Additionally, we review a body of work showing that in B. germanica, CHC profiles exhibit significant sexual dimorphism, specific CHCs act as essential precursors for female contact sex pheromone components, and we summarize the molecular regulatory mechanisms that underlie sexual dimorphism of CHC profiles. Finally, we highlight future directions and challenges in research on the biosynthesis and regulatory mechanisms of CHCs in B. germanica, and also identify potential applications of CHC studies in the pest control.

Hydrocarbons in Formicidae: influence of chemical footprints on ant behavioral strategies.

When an insect walks, it leaves chemical cues that derive from the arolium, a tarsal structure. These cues may contain important information about other species that occur in their community and can then mediate interactions of competition, predation, and information about resources with ants from their own colony. The compounds of these cues are released into the substrate in the form of chemical footprints. There are still few species studied, and little is known about the behavior of ants regarding these signals and how they use them in their interactions. Therefore, the aim of this study was to assess the behavioral strategy of different ant species when confronted with chemical footprints left by other ants, as well as identify their compounds and their relationship with the cuticular hydrocarbon profile. The experiments were performed using a Y-maze, where in one of the arms, there were chemical footprints of their own species or of other species, and the other Y arm was footprint-free. The chemical compounds of footprints and cuticle were analyzed by gas chromatography-mass spectrometry. The results show that foragers of all species detect and respond to the presence of chemical cues in the form of footprints left by other ants. Foragers of all species followed footprints of individuals of the same species both nestmates and non-nestmates; however, Neoponera villosa avoided the footprints of Cephalotes borgmeieri, and C. borgmeieri avoided the footprints of the other two species. The chemical compositions of the cuticle and footprints are related to each other and are specific to each species.

Highly diverse cuticular hydrocarbon profiles but no evidence for aggression towards non-kin in the ambrosia beetle Xyleborinus saxesenii.

Animal societies use nestmate recognition to protect against social cheaters and parasites. In most social insect societies, individuals recognize and exclude any non-nestmates and the roles of cuticular hydrocarbons as recognition cues are well documented. Some ambrosia beetles live in cooperatively breeding societies with farmed fungus cultures that are challenging to establish, but of very high value once established. Hence, social cheaters that sneak into a nest without paying the costs of nest foundation may be selected. Therefore, nestmate recognition is also expected to exist in ambrosia beetles, but so far nobody has investigated this behavior and its underlying mechanisms. Here we studied the ability for nestmate recognition in the cooperatively breeding ambrosia beetle Xyleborinus saxesenii, combining behavioural observations and cuticular hydrocarbon analyses. Laboratory nests of X. saxesenii were exposed to foreign adult females from the same population, another population and another species. Survival as well as the behaviours of the foreign female were observed. The behaviours of the receiving individuals were also observed. We expected that increasing genetic distance would cause increasing distance in chemical profiles and increasing levels of behavioural exclusion and possibly mortality. Chemical profiles differed between populations and appeared as variable as in other highly social insects. However, we found only very little evidence for the behavioural exclusion of foreign individuals. Interpopulation donors left nests at a higher rate than control donors, but neither their behaviours nor the behaviours of receiver individuals within the nest showed any response to the foreign individual in either of the treatments. These results suggest that cuticular hydrocarbon profiles might be used for communication and nestmate recognition, but that behavioural exclusion of non-nestmates is either absent in X. saxesenii or that agonistic encounters are so rare or subtle that they could not be detected by our method. Additional studies are needed to investigate this further.

Behavioural consequences of intraspecific variability in a mate recognition signal.

Mate recognition is paramount for sexually reproducing animals, and many insects rely on cuticular hydrocarbons (CHCs) for close-range sexual communication. To ensure reliable mate recognition, intraspecific sex pheromone variability should be low. However, CHCs can be influenced by several factors, with the resulting variability potentially impacting sexual communication. While intraspecific CHC variability is a common phenomenon, the consequences thereof for mate recognition remain largely unknown. We investigated the effect of CHC variability on male responses in a parasitoid wasp showing a clear-cut within-population CHC polymorphism (three distinct female chemotypes, one thereof similar to male profiles). Males clearly discriminated between female and male CHCs, but not between female chemotypes in no-choice assays. When given a choice, a preference hierarchy emerged. Interestingly, the most attractive chemotype was the one most similar to male profiles. Mixtures of female CHCs were as attractive as chemotype-pure ones, while a female-male mixture negatively impacted male responses, indicating assessment of the entire, complex CHC profile composition. Our study reveals that the evaluation of CHC profiles can be strict towards 'undesirable' features, but simultaneously tolerant enough to cover a range of variants. This reconciles reliable mate recognition with naturally occurring variability.

Impact of diapause on the cuticular hydrocarbons and physiological status of Hippodamia variegata.

The spotted amber ladybird, Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae), is known to be a potent predator of aphids, psyllids, whiteflies, mealybugs, and some butterfly species. This ladybeetle overwinters in the diapausing adult stage. The current study aimed to evaluate the impact of diapause on the energy resources and cuticular hydrocarbons (CHCs) of the female ladybeetle, specifically comparing the changes in glycogen, lipid, and protein contents, and CHCs profile of diapausing and non-diapausing adults. In this study, gas chromatography-mass was used to analyze whole-body extracts of the beetles. Results showed no significant differences between the amount of glycogen, lipid, and protein contents of diapausing and non-diapausing ladybeetle. The CHCs profile of H. variegata consisted of 24 hydrocarbons categorized into 2 groups: linear aliphatic hydrocarbons (n-alkanes) and methyl-branched hydrocarbons (17 molecules), as well as unsaturated cyclic compounds (7 molecules). The n-alkanes, with 14 compounds, were identified as the primary constituents of the CHCs of the ladybeetle. Six molecules were common to non-diapausing and diapausing beetles, 5 were exclusive to non-diapausing beetles, and 13 were exclusive to diapausing beetles. Moreover, we noted a significant difference in the quantity and quality of CHCs between diapausing and non-diapausing beetles, with diapausing beetles synthesizing more CHCs with longer chains. This disparity in CHC profiles was concluded to be an adaptation of H. variegata to survive harsh environmental conditions during diapause.

A Hitchhiker's Ride: The Honey Bee Louse Braula Coeca (Diptera: Braulidae) Selects its Host by Eavesdropping.

The bee louse Braula spp. had until recently a distribution coincident with its host the honey bee. The adult fly usually attaches to a worker honey bee and steals food from its mouth. However, not all worker bees carry Braula spp. and the mechanism used by Braula spp. to select hosts is not well understood. Using choice remounting bioassays and chemical analyses, we determined host selection and the cues used by B. coeca, a species associated with the African honey bee Apis mellifera scutellata. Braula coeca successfully remounted bees from which they were initially removed and preferred their mandibular gland pheromones (MDG) over those of bees not carrying them. The bee lice did not show any preference for the cuticular hydrocarbons of both types of workers. Chemical analyses of the MDG extracts, revealed quantitative differences between the two categories of workers, with workers carrying B. coeca having more of the queen substance (9-oxo-2(E)-decenoic acid) and worker substance (10-hydroxy-2(E)-decenoic). Braula coeca showed a dose response to the queen substance, indicating its ability to use host derived kairomones as cues that allowed it to benefit from trophallactic dominance by individuals that have a higher probability of being fed by other workers.

Chemical Camouflage Induced by Diet in a Pest Treehopper on Host Plants.

Ants patrol foliage and exert a strong selective pressure on herbivorous insects, being their primary predators. As ants are chemically oriented, some organisms that interact with them (myrmecophiles) use chemical strategies mediated by their cuticular hydrocarbons (CHCs) to deal with ants. Thus, a better understanding of the ecology and evolution of the mutualistic interactions between myrmecophiles and ants depends on the accurate recognition of these chemical strategies. Few studies have examined whether treehoppers may use an additional strategy called chemical camouflage to reduce ant aggression, and none considered highly polyphagous pest insects. We analyzed whether the chemical similarity of the CHC profiles of three host plants from three plant families (Fabaceae, Malvaceae, and Moraceae) and the facultative myrmecophilous honeydew-producing treehopper Aetalion reticulatum (Hemiptera: Aetalionidae), a pest of citrus plants, may play a role as a proximate mechanism serving as a protection against ant attacks on plants. We found a high similarity (>80%) between the CHCs of the treehoppers and two of their host plants. The treehoppers acquire CHCs through their diet, and the chemical similarity varies according to host plant. Chemical camouflage on host plants plays a role in the interaction of treehoppers with their ant mutualistic partners.

Insights into unique features of Drosophila CYP4G enzymes.

The cytochrome P450 enzymes of the CYP4G subfamily are some of the most intriguing insect P450s in terms of structure and function. In Drosophila, CYP4G1 is highly expressed in the oenocytes and is the last enzyme in the biosynthesis of cuticular hydrocarbons, while CYP4G15 is expressed in the brain and is of unknown function. Both proteins have a CYP4G-specific and characteristic amino acid sequence insertion corresponding to a loop between the G and H helices whose function is unclear. Here we address these enigmatic structural and functional features of Drosophila CYP4Gs. First, we used reverse genetics to generate D. melanogaster strains in which all or part of the CYP4G-specific loop was removed from CYP4G1. We showed that the full loop was not needed for proper folding of the P450, but it is essential for function, and that just a short stretch of six amino acids is required for the enzyme's ability to make hydrocarbons. Second, we confirmed by immunocytochemistry that CYP4G15 is expressed in the brain and showed that it is specifically associated with the cortex glia cell subtype. We then expressed CYP4G15 ectopically in oenocytes, revealing that it can produce of a blend of hydrocarbons, albeit to quantitatively lower levels resulting in only a partial rescue of CYP4G1 knockdown flies. The CYP4G1 structural variants studied here should facilitate the biochemical characterization of CYP4G enzymes. Our results also raise the question of the putative role of hydrocarbons and their synthesis by cortex glial cells.

Chemical Resemblance of Egg Surface Compounds and Dufour's Gland in Two Neotropical Polistinae Wasps Polistes versicolor (Olivier) and Mischocyttarus metathoracicus (de Saussure, 1854).

Chemical communication plays a major role in regulating social dynamics in social insect colonies. The most studied class of chemical compounds are the cuticular hydrocarbons (CHCs), compounds with high molecular weight that cover the insect body. CHCs are used in nestmate recognition and to signal reproductive status. Brood, in the form of larvae and eggs, is known to participate in chemical communication and social dynamics by performing hunger behaviour and inducing interaction with adults and conferring nest and maternity identity. CHCs of adults and egg surface compounds are similar in composition in social insect species. The main source of egg compounds is proposed to be Dufour's gland, an accessory reproductive gland found in several Hymenoptera females. There is still a lack of information about the level of similarity among CHCs, compounds of egg surface and Dufour's gland for several wasp species, which could provide correlational evidence about the origins of egg-marking compounds. Thus, we investigated whether egg surface compounds were more similar to CHCs or Dufour's gland secretions in two Neotropical primitively eusocial wasp species, Polistes versicolor (Olivier) and Mischocyttarus metathoracicus (de Saussure, 1854). As expected, there was a higher chemical similarity between eggs and Dufour's gland secretions in both studied species, supporting the hypothesis that this gland is the source of chemical compounds found over the eggs in these two primitively eusocial species.

A supergene in seaweed flies modulates male traits and female perception.

Supergenes, tightly linked sets of alleles, offer some of the most spectacular examples of polymorphism persisting under long-term balancing selection. However, we still do not understand their evolution and persistence, especially in the face of accumulation of deleterious elements. Here, we show that an overdominant supergene in seaweed flies, Coelopa frigida, modulates male traits, potentially facilitating disassortative mating and promoting intraspecific polymorphism. Across two continents, the Cf-Inv(1) supergene strongly affected the composition of male cuticular hydrocarbons (CHCs) but only weakly affected CHC composition in females. Using gas chromatography-electroantennographic detection, we show that females can sense male CHCs and that there may be differential perception between genotypes. Combining our phenotypic results with RNA-seq data, we show that candidate genes for CHC biosynthesis primarily show differential expression for Cf-Inv(1) in males but not females. Conversely, candidate genes for odorant detection were differentially expressed in both sexes but showed high levels of divergence between supergene haplotypes. We suggest that the reduced recombination between supergene haplotypes may have led to rapid divergence in mate preferences as well as increasing linkage between male traits, and overdominant loci. Together this probably helped to maintain the polymorphism despite deleterious effects in homozygotes.

A predatory social wasp does not avoid nestmates contaminated with a fungal biopesticide.

Fungus-based biopesticides have been used worldwide for crop pest control as a safer alternative to chemical pesticides such as neonicotinoids. Both agrochemicals can be lethal and may also trigger side effects on the behavioral traits of non-target social insects, which play a crucial role in providing essential biological pest control services in agroecosystems. Here, we evaluated whether a commercial formulation of the entomopathogenic fungus Beauveria bassiana or the neonicotinoid imidacloprid causes mortality in foragers of Mischocyttarus metathoracicus. These social wasps are natural enemies of caterpillars and other herbivorous insects and inhabit both urban and agricultural environments in Brazil. We also tested whether wasps discriminate between biopesticide-exposed and unexposed conspecifics. Through a combination of laboratory (survival assay) and field experiments (lure presentation), along with chemical analyses (cuticular hydrocarbon profiles), we showed that topic exposure to the label rate of each pesticide causes a lethal effect, with the biopesticide exhibiting a slower effect. Moreover, wasps do not discriminate biopesticide-exposed from unexposed conspecifics, likely because of the similarity of their cuticular chemical profiles 24 h after exposure. Overall, the delayed lethal time at the individual level, combined with the indistinctive chemical cues of exposure and the lack of discrimination by conspecifics suggests that the fungal biopesticide may ultimately pose a threat to the colony survival of this predatory wasp.

Evolution of the neuronal substrate for kin recognition in social Hymenoptera.

In evolutionary terms, life is about reproduction. Yet, in some species, individuals forgo their own reproduction to support the reproductive efforts of others. Social insect colonies for example, can contain up to a million workers that actively cooperate in tasks such as foraging, brood care and nest defence, but do not produce offspring. In such societies the division of labour is pronounced, and reproduction is restricted to just one or a few individuals, most notably the queen(s). This extreme eusocial organisation exists in only a few mammals, crustaceans and insects, but strikingly, it evolved independently up to nine times in the order Hymenoptera (including ants, bees and wasps). Transitions from a solitary lifestyle to an organised society can occur through natural selection when helpers obtain a fitness benefit from cooperating with kin, owing to the indirect transmission of genes through siblings. However, this process, called kin selection, is vulnerable to parasitism and opportunistic behaviours from unrelated individuals. An ability to distinguish kin from non-kin, and to respond accordingly, could therefore critically facilitate the evolution of eusociality and the maintenance of non-reproductive workers. The question of how the hymenopteran brain has adapted to support this function is therefore a fundamental issue in evolutionary neuroethology. Early neuroanatomical investigations proposed that social Hymenoptera have expanded integrative brain areas due to selection for increased cognitive capabilities in the context of processing social information. Later studies challenged this assumption and instead pointed to an intimate link between higher social organisation and the existence of developed sensory structures involved in recognition and communication. In particular, chemical signalling of social identity, known to be mediated through cuticular hydrocarbons (CHCs), may have evolved hand in hand with a specialised chemosensory system in Hymenoptera. Here, we compile the current knowledge on this recognition system, from emitted identity signals, to the molecular and neuronal basis of chemical detection, with particular emphasis on its evolutionary history. Finally, we ask whether the evolution of social behaviour in Hymenoptera could have driven the expansion of their complex olfactory system, or whether the early origin and conservation of an olfactory subsystem dedicated to social recognition could explain the abundance of eusocial species in this insect order. Answering this question will require further comparative studies to provide a comprehensive view on lineage-specific adaptations in the olfactory pathway of Hymenoptera.

Jinggangmycin stimulates reproduction and increases CHCs-dependent desiccation tolerance in Drosophila melanogaster.

Jinggangmycin (JGM), an agricultural antibiotic compound, is mainly used against the rice sheath blight (RSB) Rhizoctonia solani. However, its application may lead to unexpected consequences in insects. In this study, the effects of JGM on the physiological parameters of Drosophila melanogaster were investigated. The results showed that 0.005 g/ml JGM exposure increased female daily egg production and extended the oviposition period, while there was no significant effect on reproduction at 0.016 g/ml. At the same time, desiccation tolerance increased in flies fed 0.005 g/ml JGM. The RT-qPCR results revealed that FAS1 and FAS3 expression were upregulated in 0.005 g/ml JGM treated flies. Consistently, the amount of CHCs accumulated on the cuticle surface increased upon JGM treatment at 0.005 g/ml. Moreover, RNAi for FAS3 decreased desiccation tolerance of JGM-treated flies. These results suggest that JGM affects fatty acid biosynthesis, which in turn enhances reproduction and desiccation tolerance in Drosophila.

Queen fecundity, worker entourage and cuticular chemistry in the ant Formica fusca.

Cooperative breeding entails conflicts over reproductive shares that may be settled in different ways. In ants, where several queens simultaneously reproduce in a colony, both queens and workers may influence the reproductive apportionment and offspring quality. Queens may vary in their intrinsic fecundity, which may influence the size of the worker entourage attending individual queens, and this may eventually dictate the reproductive output of a queen. We tested whether the reproductive success of queens is affected by the size of their worker entourage, their fecundity at the onset of the reproductive season, and whether the queen cuticular hydrocarbon profile carries information on fecundity. We show that in the ant Formica fusca both queen fecundity and egg hatching success increase with the size of their entourage, and that newly hatched larvae produced by initially highly fecund queens are smaller. Furthermore, higher relatedness among workers increased queen fecundity. Finally, the queens that received a large worker entourage differed in the cuticular chemistry from those that received a small worker entourage. Our results thus show that workers play a pivotal role in determining queen fitness, that high intracolony relatedness among workers enhances the overall reproductive output in the colony, and that queen fecundity is reflected in their cuticular hydrocarbon profile.

Beauty or function? The opposing effects of natural and sexual selection on cuticular hydrocarbons in male black field crickets.

Although many theoretical models of male sexual trait evolution assume that sexual selection is countered by natural selection, direct empirical tests of this assumption are relatively uncommon. Cuticular hydrocarbons (CHCs) are known to play an important role not only in restricting evaporative water loss but also in sexual signalling in most terrestrial arthropods. Insects adjusting their CHC layer for optimal desiccation resistance is often thought to come at the expense of successful sexual attraction, suggesting that natural and sexual selection are in opposition for this trait. In this study, we sampled the CHCs of male black field crickets (Teleogryllus commodus) using solid-phase microextraction and then either measured their evaporative water loss or mating success. We then used multivariate selection analysis to quantify the strength and form of natural and sexual selection targeting male CHCs. Both natural and sexual selection imposed significant linear and stabilizing selection on male CHCs, although for very different combinations. Natural selection largely favoured an increase in the total abundance of CHCs, especially those with a longer chain length. In contrast, mating success peaked at a lower total abundance of CHCs and declined as CHC abundance increased. However, mating success did improve with an increase in a number of specific CHC components that also increased evaporative water loss. Importantly, this resulted in the combination of male CHCs favoured by natural selection and sexual selection being strongly opposing. Our findings suggest that the balance between natural and sexual selection is likely to play an important role in the evolution of male CHCs in T. commodus and may help explain why CHCs are so divergent across populations and species.

Decoding the genetic and chemical basis of sexual attractiveness in parasitic wasps.

Attracting and securing potential mating partners is of fundamental importance for reproduction. Therefore, signaling sexual attractiveness is expected to be tightly coordinated in communication systems synchronizing senders and receivers. Chemical signaling has permeated through all taxa of life as the earliest and most widespread form of communication and is particularly prevalent in insects. However, it has been notoriously difficult to decipher how exactly information related to sexual signaling is encoded in complex chemical profiles. Similarly, our knowledge of the genetic basis of sexual signaling is very limited and usually restricted to a few case studies with comparably simple pheromonal communication mechanisms. The present study jointly addresses these two knowledge gaps by characterizing two fatty acid synthase genes that most likely evolved by tandem gene duplication and that simultaneously impact sexual attractiveness and complex chemical surface profiles in parasitic wasps. Gene knockdown in female wasps dramatically reduces their sexual attractiveness coinciding with a drastic decrease in male courtship and copulation behavior. Concordantly, we found a striking shift of methyl-branching patterns in the female surface pheromonal compounds, which we subsequently demonstrate to be the main cause for the greatly reduced male mating response. Intriguingly, this suggests a potential coding mechanism for sexual attractiveness mediated by specific methyl-branching patterns in complex cuticular hydrocarbon (CHC) profiles. So far, the genetic underpinnings of methyl-branched CHCs are not well understood despite their high potential for encoding information. Our study sheds light on how biologically relevant information can be encoded in complex chemical profiles and on the genetic basis of sexual attractiveness.

Attracting a mate is critical in all species that sexually reproduce. Most animals, particularly insects, do this using chemical compounds called pheromones which can be sensed by potential mates. But how these vast range of different compounds encode and convey the information needed to secure a partner is not fully understood, and the genes that drive this complex communication mechanism are largely unknown. To address this knowledge gap, Sun et al. studied the parasitic wasp Nasonia vitripennis. Like other insects, female N. vitripennis contain a wide range of chemical compounds on their cuticle, the outer waxy layer coating their surface. Sun et al. set out to find exactly which of these compounds, known as cuticular hydrocarbons, are involved in sexual communication. They did this by simultaneously inactivating two related genes that they hypothesized to be responsible for synthesizing and maintaining chemical compounds on the cuticle of insects. The genetic modification altered the pattern of chemicals on the surface of the female wasps by specifically up- and down-regulating compounds with similar branching structures. The mutant females were also much less sexually attractive to male wasps. These findings suggest that the chemical pattern identified by Sun et al. is responsible for communicating and maintaining sexual attractiveness in N. vitripennis female wasps. This is a significant stepping stone towards unravelling how sexual attractiveness can be encoded in complex mixtures of pheromones. The results also have important implications for agriculture, as this parasitic wasp species is routinely used to exterminate particular fly populations that cause agricultural damage. The work by Sun et al. provides new insights into how these wasps sexually communicate, which may help scientists improve their rearing conditions and sustain them over multiple generations. This could contribute to a wider application of this more sustainable, eco-friendly alternative to destructive agricultural pesticides.

Olfaction is essential for nest recognition in solitary Hymenoptera.

Flying insects are believed to rely primarily on visual cues for orientation, with chemical cues often being overlooked. In the case of solitary bees and wasps, being able to return successfully to their nests and provision their brood cells is paramount for the survival of the species. While vision has been shown to be involved in pinpointing the nest location, our results confirm that olfaction is important in nest recognition. The large diversity in nesting strategies observed among solitary Hymenoptera makes them an excellent model to comparatively study the use of olfactory cues from the nesting individual for nest recognition. We have analyzed the chemical profiles of three nesting bees (Osmia spp.) and one wasp (Sceliphron curvatum) and that of their nest entrances. A striking match in the identified chemicals was revealed between each nest and its occupant. When the chemicals were removed from the nest, a clear behavioral response could be observed for Osmia cornuta. This shows the importance of olfactory cues in complementing visual orientation for precise homing in a solitary species, thereby opening up various promising biological questions in the fields of sensory perception and complementation, or the trade-offs of nest aggregation and associated costs.

Termite cuticular extracts improve acceptance of bait for controlling invasive Asian needle ants, Brachyponera chinensis.

BACKGROUND: The Asian needle ant, Brachyponera chinensis, is an invasive ant currently spreading in urban and natural habitats throughout the eastern United States. Recent studies have documented the negative impact of B. chinensis on native ecosystems and human health, yet effective control strategies are lacking. Control difficulties are, in part, due to the unique biology of B. chinensis, which is a predatory ant and a termite specialist. Given that subterranean termites are an important nutritional resource for B. chinensis, the current study evaluated the potential of termite cuticular extract to improve the target-specificity and efficacy of commercial bait used for B. chinensis control. RESULTS: The efficacy of bait augmented with termite cuticular extracts was evaluated in laboratory and field trials. In laboratory assays, B. chinensis colonies were offered granular bait treated with termite cuticular extract. Results demonstrated that the acceptance of commercial bait is significantly increased by the addition of termite cuticular extract or synthetic (Z)-9-pentacosene, a major component of termite cuticular extract. Foraging activity of Asian needle ants was significantly greater on baits augmented with termite cuticular extract or (Z)-9-pentacosene relative to standard bait. Furthermore, bait augmented with termite cuticular extract worked substantially faster relative to standard bait. To evaluate population effects, field studies were conducted in forested areas invaded by B. chinensis. Bait treated with termite cuticular extract scattered on the forest floor provided rapid control of B. chinensis and ant densities throughout the treated plots declined by 98% within 14 days. CONCLUSION: The incorporation of termite cuticular extracts and individual cuticular hydrocarbons such as (Z)-9-pentacosene into traditional baits used for B. chinensis control may offer a novel tool to manage this increasingly problematic invasive ant. © 2023 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.