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.

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.

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.

Variations in cuticular hydrocarbons of Calliphora vicina (Diptera: Calliphoridae) empty puparia: Insights for estimating late postmortem intervals.

Necrophagous flies, particularly blowflies, serve as vital indicators in forensic entomology and ecological studies, contributing to minimum postmortem interval estimations and environmental monitoring. The study investigates variations in the predominant cuticular hydrocarbons (CHCs) viz. n-C25, n-C27, n-C28, and n-C29 of empty puparia of Calliphora vicina Robineau-Desvoidy, 1830, (Diptera: Calliphoridae) across diverse environmental conditions, including burial, above-ground and indoor settings, over 90 days. Notable trends include a significant decrease in n-C25 concentrations in buried and above-ground conditions over time, while n-C27 concentrations decline in buried and above-ground conditions but remain stable indoors. Burial conditions show significant declines in n-C27 and n-C29 concentrations over time, indicating environmental influences. Conversely, above-ground conditions exhibit uniform declines in all hydrocarbons. Indoor conditions remain relatively stable, with weak correlations between weathering time and CHC concentrations. Additionally, machine learning techniques, specifically Extreme Gradient Boosting (XGBoost), are employed for age estimation of empty puparia, yielding accurate predictions across different outdoor and indoor conditions. These findings highlight the subtle responses of CHC profiles to environmental stimuli, underscoring the importance of considering environmental factors in forensic entomology and ecological research. The study advances the understanding of insect remnant degradation processes and their forensic implications. Furthermore, integrating machine learning with entomological expertise offers standardized methodologies for age determination, enhancing the reliability of entomological evidence in legal contexts and paving the way for future research and development.

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.

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.

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.

The cytochrome P450 gene CYP4g1 driven by high temperature confers abamectin tolerance on Liriomyza trifolii through promoting cuticular hydrocarbons biosynthesis.

Liriomyza trifolii, an invasive pest, poses a substantial threat to horticultural and vegetable plants. It spreads rapidly, especially in hot weather, leading to large-scale outbreaks with strong thermotolerance and insecticide resistance. In this study, mortality and LtCYP4g1 expression in L. trifolii were evaluated after thermal and insecticides exposure. Furthermore, functional verification of LtCYP4g1 was conducted through RNA interference and bacterial survival assays in Escherichia coli containing recombinant LtCYP4g1 protein. Results indicated that a short time exposure to high temperature incresed insecticide tolerance of L. trifolii, attributed to decreased mortality and induced LtCYP4g1 expression; LtCYP4g1 was involved in stimulating synthesis of cuticular hydrocarbons (CHCs) and elevating epicuticle lipid content and thickness, and E. coli cells overexpressing LtCYP4g1 exhibited significant tolerance to thermal and insecticide stress. In general, P450-mediated tolerance of L. trifolii was enhanced by high temperature, with LtCYP4g1 playing a role in promoting biosynthesis of CHCs for thickening epidermal lipid barrier and reducing cuticular penetration. This study provides a framework for delving into the function of CYP450s in insecticide detoxification and illustrates the role of global warming in driving the evolution of L. trifolii.

Gene expression differences consistent with water loss reduction underlie desiccation tolerance of natural Drosophila populations.

BACKGROUND: Climate change is one of the main factors shaping the distribution and biodiversity of organisms, among others by greatly altering water availability, thus exposing species and ecosystems to harsh desiccation conditions. However, most of the studies so far have focused on the effects of increased temperature. Integrating transcriptomics and physiology is key to advancing our knowledge on how species cope with desiccation stress, and these studies are still best accomplished in model organisms. RESULTS: Here, we characterized the natural variation of European D. melanogaster populations across climate zones and found that strains from arid regions were similar or more tolerant to desiccation compared with strains from temperate regions. Tolerant and sensitive strains differed not only in their transcriptomic response to stress but also in their basal expression levels. We further showed that gene expression changes in tolerant strains correlated with their physiological response to desiccation stress and with their cuticular hydrocarbon composition, and functionally validated three of the candidate genes identified. Transposable elements, which are known to influence stress response across organisms, were not found to be enriched nearby differentially expressed genes. Finally, we identified several tRNA-derived small RNA fragments that differentially targeted genes in response to desiccation stress. CONCLUSIONS: Overall, our results showed that basal gene expression differences across individuals should be analyzed if we are to understand the genetic basis of differential stress survival. Moreover, tRNA-derived small RNA fragments appear to be relevant across stress responses and allow for the identification of stress-response genes not detected at the transcriptional level.

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.

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.

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.

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.

Chemical signatures of egg maternity and Dufour's gland in Vespine wasps.

Cuticular hydrocarbons (CHCs) are often used in the chemical communication among social insects. CHCs can be used in nestmate recognition and as queen pheromones, the latter allows the regulation of the reproductive division of labor. In the common wasp Vespula vulgaris, CHCs and egg-marking hydrocarbons are caste-specific, being hydrocarbon queen pheromones and egg maternity signals. Whether these compounds are conserved among other Vespinae wasps remains unknown. Queens, virgin queens, reproductive workers, and workers belonging to four different wasp species, Dolichovespula media, Dolichovespula saxonica, Vespa crabro, and Vespula germanica, were collected and studied. The cuticular hydrocarbons, egg surface, and Dufour's gland composition were characterized and it was found that chemical compounds are caste-specific in the four species. Quantitative and qualitative differences were detected in the cuticle, eggs, and Dufour's gland. Some specific hydrocarbons that were shown to be overproduced in the cuticle of queens were also present in higher quantities in queen-laid eggs and in their Dufour's gland. These hydrocarbons can be indicated as putative fertility signals that regulate the division of reproductive labor in these Vespine societies. Our results are in line with the literature for V. vulgaris and D. saxonica, in which hydrocarbons were shown to be conserved queen signals. This work presents correlative evidence that queen chemical compounds are found not only over the body surface of females but also in other sources, such as the Dufour's gland and eggs.

High Divergence of Cuticular Hydrocarbons and Hybridization Success in Two Allopatric Seven-Spot Ladybugs.

The seven-spotted ladybug is a widespread species in the Palearctic, and also acclimated in the Nearctic. It has been classified into different species on the basis of certain morphological characteristics, the geographical origin, and the genitalia structure of both sexes. The morphotypes of North Africa and the Canary Islands are separated, under the name of Coccinella algerica Kovár, 1977, from the rest of the Palearctic and Nearctic populations of Coccinella septempunctata Linnaeus, 1758. In this study, we investigated, on one hand, whether potential reproductive barriers have been established during evolution between the geographically isolated North African and the European seven-spotted ladybugs by performing reciprocal crosses. On the other hand, we assessed their cuticular hydrocarbon (CHC) divergence by GC-MS. The 33 CHCs indentified are with a skeleton of 23 to 32 carbon atoms. These CHCs are linear alkanes (24.9 ± 3.6%) and methyl-branched alkanes (75.1 ± 3.6%) including monomethylalkanes (48.8 ± 2.4%), dimethylalkanes (24.6 ± 4.0%) and trimethylalkanes (2.0 ± 1.0%). Although all the CHC compounds identified are present in the two seven-spotted ladybugs and their F1 and F2 hybrids, their profiles diverged significantly. However, these chemical divergences have not altered the sexual communication to cause reproductive isolation. The two ladybugs interbreed and leave viable and fertile offspring, with even a heterosis effect on reproductive performances, without phenotypic degradation after the F1 generation. So, these chemical differences are just an intraspecific variability in response to heterogeneous environments. The two types of ladybugs can be considered as two different races of the same species with reduced genetic divergence.

The Cuticular Hydrocarbons of Dasineura Oleae Show Differences Between Sex, Adult Age and Mating Status.

In insects, cuticular lipids prevent water loss and act as semiochemicals. Because of their ecological function, the profile change across the insects' sex and development offers insight into insect biology and possible tools for pest management. Here, the first work on cecidomyiid cuticular extracts is proposed considering Dasineura oleae (Diptera: Cecidomyiidae) males and females at different adult ages (0-12 h, 12-24 h, 24-36 h) and distinct sexual conditions (virgin and mated). A set of 49 compounds were recorded (12 alkanes, 1 monomethyl alkane, 11 fatty acids, 4 esters, 1 aldehyde, 1 allylbenzene, 1 amine, 1 flavonoid, 1 ketone, 1 phenol, 1 steradiene, 1 sterol, 1 terpene, 1 triterpene and 11 unknown compounds), and 18 of them showed significant differences between groups. Among alkanes, hexacosane (nC26) exhibited a decreasing trend from the youngest to the oldest females, while pentacosane (nC25) and nonacosane (nC29) showed a decreasing trend from 0 to 12 h to 12-24 h virgin females. In addition, nonadecane (nC19) was significantly more abundant in the youngest males compared to older males and females. The alkanes nC25, nC26 and nC29 have been reported to be age-related also in other dipterans, while nC19 has been described as gender-specific chemical cue for platygastrid parasitoids. Further behavioural trials and analyses are required to assign the specific ecological roles to the characterized compounds. Our results may contribute to develop new low-impact control strategies relying on the manipulation of D. oleae's chemical communication (e.g. disruption of mating or species recognition). HIGHLIGHTS: • Cuticular hydrocarbons are often involved in dipteran intraspecific communication. • We explored the cuticular profile of D. oleae at different age, sex, mating condition. • Five alkanes and one mono-methyl alkane showed differences among groups. • Linoleic acid is the most abundant compound in virgins, absent in mated insects. • Eleven compounds disappear in mated insects, but were present in all virgins.

Immune Stimulation via Wounding Alters Chemical Profiles of Adult Tribolium castaneum.

Group-living individuals experience immense risk of disease transmission and parasite infection. In social and in some non-social insects, disease control with immunomodulation arises not only via individual immune defenses, but also via infochemicals such as contact cues and (defensive) volatiles to mount a group-level immunity. However, little is known about whether activation of the immune system elicits changes in chemical phenotypes, which may mediate these responses. We here asked whether individual immune experience resulting from wounding or injection of heat-killed Bacillus thuringiensis (priming) leads to changes in the chemical profiles of female and male adult red flour beetles, Tribolium castaneum, which are non-social but gregarious. We analyzed insect extracts using GC-FID to study the chemical composition of (1) cuticular hydrocarbons (CHCs) as candidates for the transfer of immunity-related information between individuals via contact, and (2) stink gland secretions, with analysis of benzoquinones as main active compounds regulating 'external immunity'. Despite a pronounced sexual dimorphism in CHC profiles, wounding stimulation led to similar profile changes in males and females with increases in the proportion of methyl-branched alkanes compared to naïve beetles. While changes in the overall secretion profiles were less pronounced, absolute amounts of benzoquinones were transiently elevated in wounded compared to naïve females. Responses to priming were insignificant in CHCs and secretions. We suggest that changes in different infochemicals after wounding may mediate immune status signaling in the context of both internal and external immune responses in groups of this non-social insect, thus showing parallels to social immunity.

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.

Why do ants differ in acclimatory ability? Biophysical mechanisms behind cuticular hydrocarbon acclimation across species.

Maintaining water balance is vital for terrestrial organisms. Insects protect themselves against desiccation via cuticular hydrocarbons (CHCs). CHC layers are complex mixtures of solid and liquid hydrocarbons, with a surprisingly diverse composition across species. This variation may translate into differential phase behaviour, and hence varying waterproofing capacity. This is especially relevant when temperatures change, which requires acclimatory CHC changes to maintain waterproofing. Nevertheless, the physical consequences of CHC variation are still little understood. We studied acclimatory responses and their consequences for CHC composition, phase behaviour and drought survival in three congeneric ant species. Colony sub-groups were kept under cool, warm and fluctuating temperature regimes. Lasius niger and Lasius platythorax, both of which are rich in methyl-branched alkanes, showed largely predictable acclimatory changes of the CHC profile. In both species, warm acclimation increased drought resistance. Warm acclimation increased the proportion of solid compounds in L. niger but not in L. platythorax. In both species, the CHC layer formed a liquid matrix of constantly low viscosity, which contained highly viscous and solid parts. This phase heterogeneity may be adaptive, increasing robustness to temperature fluctuations. In Lasius brunneus, which is rich in unsaturated hydrocarbons, acclimatory CHC changes were less predictable, and warm acclimation did not enhance drought survival. The CHC layer was more homogeneous, but matrix viscosity changed with acclimation. We showed that ant species use different physical mechanisms to enhance waterproofing during acclimation. Hence, the ability to acclimate, and thus climatic niche breadth, may strongly depend on species-specific CHC profile.

Insect cuticular hydrocarbon composition influences their interaction with spider capture threads.

Insects represent the main prey of spiders, and spiders and insects co-diversified in evolutionary history. One of the main features characterizing spiders is their web as a trap to capture prey. Phylogenetically, the cribellate thread is one of the earliest thread types that was specialized to capture prey. In contrast to other capture threads, it lacks adhesive glue and consists of nanofibres, which do not only adhere to insects via van der Waals forces but also interact with the insects' cuticular hydrocarbon (CHC) layer, thus enhancing adhesion. The CHC layer consists of multiple hydrocarbon types and is highly diverse between species. In this study, we show that CHC interaction with cribellate capture threads is affected by CHC composition of the insect. We studied the interaction in detail for four insect species with different CHC profiles and observed a differential migration of CHCs into the thread. The migration depends on the molecular structure of the hydrocarbon types as well as their viscosity, influenced by the ambient temperature during the interaction. As a consequence, adhesion forces to CHC layers differ depending on their chemical composition. Our results match predictions based on biophysical properties of hydrocarbons, and show that cribellate spiders can exert selection pressure on the CHC composition of their insect prey.