Lipids of the insect cuticle: origin, composition and function

Chemical basis of nest-mate discrimination in the ant Formica exsecta

Distinguishing nest-mates from non-nest-mates underlies key animal behaviours, such as territoriality, altruism and the evolution of sociality. Despite its importance, there is very little empirical support for such a mechanism in nature. Here we provide data that the nest-mate recognition mechanism in an ant is based on a colony-specific Z9-alkene signature, proving that surface chemicals are indeed used in ant nest-mate recognition as was suggested 100 years ago. We investigated the cuticular hydrocarbon profiles of 10 Formica exsecta colonies that are composed almost entirely of a Z9-alkene and alkane component. Then we showed that worker aggression is only elicited by the Z9-alkene part. This was confirmed using synthetic Z9-alkene and alkane blends matched to the individual colony profiles of the two most different chemical colonies. In both colonies, only glass beads with 'nest-mate' alkene profiles received reduced aggression. Finally, changing the abundance of a single Z9-alkene on live ants was shown to significantly increase the aggression they received from nest-mates in all five colonies tested. Our data suggest that nest-mate discrimination in the social insects has evolved to rely upon highly sensitive responses to relatively few compounds.

Egg marking in the facultatively queenless ant Gnamptogenys striatula: the source and mechanism

Conflicts over reproductive division of labour are common in social insects. These conflicts are often resolved via antagonistic actions that are mediated by chemical cues. Dominant egg layers and their eggs can be recognized by a specific yet similar cuticular hydrocarbon profile. In the facultatively queenless ant Gnamptogenys striatula, a worker's cuticular hydrocarbon profile signals its fertility and this determines its position in the reproductive division of labour. How eggs acquire the same hydrocarbon profile is as yet unclear. Here, we search for glandular sources of egg hydrocarbons and identify the putative mechanism of egg marking. We found that eggs carry the same hydrocarbons as the cuticle of fertile workers, and that these hydrocarbons also occur in the ovaries and the haemolymph. None of the studied glands (Dufour, venom, labial and mandibular gland) contained these hydrocarbons. Our results indicate that hydrocarbons are deposited on eggs while still in the ovaries. The low hydrocarbon concentration in the ovaries, however, suggests they are produced elsewhere and transported through the haemolymph. We also found that fertile workers regularly deposit new hydrocarbons on eggs by rubbing laid eggs with a hairy structure on the abdominal tip from which a non-polar substance is secreted.

Nestmate recognition in ants is possible without tactile interaction

Ants of the genus Camponotus are able to discriminate recognition cues of colony members (nestmates) from recognition cues of workers of a different colony (non-nestmates) from a distance of 1 cm. Free moving, individual Camponotus floridanus workers encountered differently treated dummies on a T-bar and their behavior was recorded. Aggressive behavior was scored as mandibular threat towards dummies. Dummies were treated with hexane extracts of postpharyngeal glands (PPGs) from nestmates or non-nestmates which contain long-chain hydrocarbons in ratios comparable to what is found on the cuticle. The cuticular hydrocarbon profile bears cues which are essential for nestmate recognition. Although workers were prevented from antennating the dummies, they showed significantly less aggressive behavior towards dummies treated with nestmate PPG extracts than towards dummies treated with non-nestmate PPG extracts. In an additional experiment, we show that cis-9-tricosene, an alkene naturally not found in C. floridanus' cuticular profile, is behaviorally active and can interfere with nestmate recognition when presented together with a nestmate PPG extract. Our study demonstrates for the first time that the complex multi-component recognition cues can be perceived and discriminated by ants at close range. We conclude that contact chemosensilla are not crucial for nestmate recognition since tactile interaction is not necessary.

The role of cuticular hydrocarbons in mating and conspecific recognition in the closely related longicorn beetles Pidonia grallatrix and P. takechii

The role of cuticular chemicals in mating behavior and their chemical components were studied in two sympatric flower-visiting longicorn beetles, Pidonia grallatrix and P. takechii. Mating experiments revealed that female cuticular chemicals elicit male mating behavior and that males can discriminate between conspecific and heterospecific females on the basis of contact chemicals. GC-MS analyses of whole-body extracts in the two species and both sexes determined that extracts contained a series of hydrocarbons including n-alkanes, n-alkenes, and methylalkanes. The relative abundance of some hydrocarbons differed between species and sexes, and canonical discriminant analysis showed discrimination of species and sex could be made unambiguously with several compounds. These results imply that the difference in cuticular hydrocarbons facilitates the premating isolation of sympatric Pidonia species.

Chemical deterrent enables a socially parasitic ant to invade multiple hosts

Social parasites are involved in a coevolutionary arms race, which drives increasing specialization resulting in a very narrow host range. The Formicoxenus ants are a small group of social parasites with a xenobiotic lifestyle. Formicoxenus quebecensis and Formicoxenus provancheri are highly specialized ants using chemical mimicry to blend into their respective Myrmica ant host colonies. However, Formicoxenus nitidulus is unique in being able to survive in over 11 different ant host species. We observed that when live or dead F. nitidulus adults are seized by their host they are immediately dropped undamaged, despite possessing a cuticular hydrocarbon profile that differs markedly from its host. Hexane extracts of the F. nitidulus cuticle made previously acceptable prey items unattractive to their Formica host, indicating a chemical deterrent effect. This is the first time that a social parasite has been shown to exploit the generalized deterrence strategy to avoid host aggression over long periods of time. This supports the idea that coevolved and generalist diseases or parasites require fundamentally different defence mechanisms. We suggest that F. nitidulus uses its cuticular chemistry, possible alkadienes, as a novel deterrent mechanism to allow it to switch hosts easily and so become a widespread and abundant social parasite.

The smell of parents: breeding status influences cuticular hydrocarbon pattern in the burying beetle Nicrophorus vespilloides

The waxy layer of the cuticle has been shown to play a fundamental role in recognition systems of insects. The biparental burying beetle Nicrophorus vespilloides is known to have the ability to discriminate between breeding and non-breeding conspecifics and also here cuticular substances could function as recognition cue. However, it has not yet been demonstrated that the pattern of cuticular lipids can reflect the breeding status of a beetle or of any other insect. With chemical analysis using coupled gas chromatography-mass spectrometry, we showed that the chemical signature of N. vespilloides males and females is highly complex and changes its feature with breeding status. Parental beetles were characterized by a higher amount of some unusual unsaturated hydrocarbons than beetles which are not caring for larvae. The striking correlation between cuticular profiles and breeding status suggests that cuticular hydrocarbons inform the beetles about parental state and thus enable them to discriminate between their breeding partner and a conspecific intruder. Furthermore, we found evidence that nutritional conditions also influence the cuticular profile and discuss the possibility that the diet provides the precursors for the unsaturated hydrocarbons observed in parental beetles. Our study underlines the fact that the cuticular pattern is rich of information and plays a central role in the burying beetles' communication systems.

The antibacterial protein lysozyme identified as the termite egg recognition pheromone

Social insects rely heavily on pheromone communication to maintain their sociality. Egg protection is one of the most fundamental social behaviours in social insects. The recent discovery of the termite-egg mimicking fungus ‘termite-ball’ and subsequent studies on termite egg protection behaviour have shown that termites can be manipulated by using the termite egg recognition pheromone (TERP), which strongly evokes the egg-carrying and -grooming behaviours of workers. Despite the great scientific and economic importance, TERP has not been identified because of practical difficulties. Herein we identified the antibacterial protein lysozyme as the TERP. We isolated the target protein using ion-exchange and hydrophobic interaction chromatography, and the MALDI-TOF MS analysis showed a molecular size of 14.5 kDa. We found that the TERP provided antibacterial activity against a gram-positive bacterium. Among the currently known antimicrobial proteins, the molecular size of 14.5 kDa limits the target to lysozyme. Termite lysozymes obtained from eggs and salivary glands, and even hen egg lysozyme, showed a strong termite egg recognition activity. Besides eggs themselves, workers also supply lysozyme to eggs through frequent egg-grooming, by which egg surfaces are coated with saliva containing lysozyme. Reverse transcript PCR analysis showed that mRNA of termite lysozyme was expressed in both salivary glands and eggs. Western blot analysis confirmed that lysozyme production begins in immature eggs in queen ovaries. This is the first identification of proteinaceous pheromone in social insects. Researchers have focused almost exclusively on hydrocarbons when searching for recognition pheromones in social insects. The present finding of a proteinaceous pheromone represents a major step forward in, and result in the broadening of, the search for recognition pheromones. This novel function of lysozyme as a termite pheromone illuminates the profound influence of pathogenic microbes on the evolution of social behaviour in termites.

Foraging scent marks of bumblebees: footprint cues rather than pheromone signals

In their natural habitat foraging bumblebees refuse to land on and probe flowers that have been recently visited (and depleted) by themselves, conspecifics or other bees, which increases their overall rate of nectar intake. This avoidance is often based on recognition of scent marks deposited by previous visitors. While the term 'scent mark' implies active labelling, it is an open question whether the repellent chemicals are pheromones actively and specifically released during flower visits, or mere footprints deposited unspecifically wherever bees walk. To distinguish between the two possibilities, we presented worker bumblebees (Bombus terrestris) with three types of feeders in a laboratory experiment: unvisited control feeders, passive feeders with a corolla that the bee had walked over on its way from the nest (with unspecific footprints), and active feeders, which the bee had just visited and depleted, but which were immediately refilled with sugar-water (potentially with specific scent marks). Bumblebees rejected both active and passive feeders more frequently than unvisited controls. The rate of rejection of passive feeders was only slightly lower than that of active feeders, and this difference vanished completely when passive corollas were walked over repeatedly on the way from the nest. Thus, mere footprints were sufficient to emulate the repellent effect of an actual feeder visit. In confirmation, glass slides on which bumblebees had walked on near the nest entrance accumulated hydrocarbons (alkanes and alkenes, C23 to C31), which had previously been shown to elicit repellency in flower choice experiments. We conclude that repellent scent marks are mere footprints, which foraging bees avoid when they encounter them in a foraging context.

Reformation process of the neuronal template for nestmate-recognition cues in the carpenter ant Camponotus floridanus

Ants use cuticular hydrocarbons (CHC-profiles) as multicomponent recognition cues to identify colony members (nestmates). Recognition cues (label) are thought to be perceived during ant-ant encounters and compared to a neuronal template that represents the colony label. Over time, the CHC-profile may change, and the template is adjusted accordingly. A phenotype mismatch between label and template, as happens with CHC-profiles of foreign workers (non-nestmates), frequently leads to aggressive behavior. We investigated the template reformation in workers of the carpenter ant Camponotus floridanus by masking their antennae with postpharyngeal gland (PPG) extracts from nestmates or non-nestmates. The behavioral response of manipulated workers encountering unmanipulated workers was measured independently after 2 and after 15 h. After 2 h of incubation, workers treated with either of the two PPG-extracts showed low aggression towards nestmates and high aggression towards non-nestmates. In contrast, after 15 h of incubation, workers treated with non-nestmate PPG-extract showed low aggression towards both nestmates and non-nestmates. The slow (>2 h) adjustment of the template indicates a reformation localized in the central nervous system rather than in chemosensory neurons. In addition, our data show that template adjustment to a new CHC-profile does not impair the assessment of the old CHC-profile as nestmate label.

Courtship pheromones in parasitic wasps: comparison of bioactive and inactive hydrocarbon profiles by multivariate statistical methods

Cuticular hydrocarbons play a significant role in the regulation of cuticular permeability and also in the chemical communication of insects. In the parasitoid Lariophagus distinguendus (Hymenoptera: Pteromalidae), male courtship behavior is mediated by a female-produced sex pheromone. Previous studies have shown that the chemicals involved are already present in the pupal stage of both males and females. However, pheromonal activity in males decreases shortly after emergence. This pheromonal deactivation occurs only in living males, suggesting an active process rather than simple evaporation of bioactive compounds. Here, we present evidence that the sex pheromone of L. distinguendus is composed of a series of cuticular hydrocarbons. Filter paper disks treated with nonpolar fractions of cuticular extracts of freshly emerged males and females, 72-hr-old females, and yellowish pupae caused arrestment and stimulated key elements of courtship behavior in males, whereas fractions of 72-hr-old males did not. Sixty-four hydrocarbons with chain length between C(25) and C(37) were identified in the fractions by gas chromatography-mass spectrometry (GC-MS). Methyl-branched alkanes with one to four methyl groups were major components, along with traces of n-alkanes and monoalkenes. Principal component analysis, based on the relative amounts of the compounds, revealed that cuticular hydrocarbon composition differed among all five groups. By using partial least squares-discriminant analysis, we determined a series of components that differentiate bioactive and bioinactive hydrocarbon profiles, and may be responsible for pheromonal activity of hydrocarbon fractions in L. distinguendus.

Structural complexity of chemical recognition cues affects the perception of group membership in the ants Linephithema humile and Aphaenogaster cockerelli

Hydrocarbon profiles on the cuticle of social insects act as multi-component recognition cues used to identify membership in a species, a colony or, within colonies, cues about its reproductive status or task group. To examine the role of structural complexity in ant hydrocarbon recognition cues, we studied the species recognition response of two ant species, Linepithema humile and Aphaenogaster cockerelli, and the recognition of conspecifics by L. humile. The cuticular hydrocarbons of ants are composed of molecules of varying chain lengths from three structural classes, n-alkanes, methyl-branched alkanes and n-alkenes. We employed species recognition bioassays that measured the aggressive response of both species of ants to mixtures of hydrocarbon classes, single structural classes of hydrocarbons (n-alkanes,methyl-branched alkanes and n-alkenes), and controls. The results showed that a combination of at least two hydrocarbon structural classes was necessary to elicit an aggressive species recognition response. Moreover, no single class of hydrocarbons was more important than the others in eliciting a response. Similarly, in the recognition of conspecifics, Linepithema humile did not respond to a mixture of n-alkane cuticular hydrocarbons presented alone, but supplementation of nestmate hydrocarbon profiles with the n-alkanes did elicit high levels of aggression. Thus both L. humile and A. cockerelli required mixtures of hydrocarbons of different structural classes to recognize species and colony membership. It appears that information on species and colony membership is not in isolated components of the profile, but instead in the mixture of structural classes found in cuticular hydrocarbon profiles.

Identification of termite species and subspecies of the genus Zootermopsis using near-infrared reflectance spectroscopy

Dampwood termites of the genus Zootermopsis (Isoptera: Termopsidae) are an abundant group of basal termites found in temperate forests of western North America. Three species are currently recognized in the genus and one of these species is subdivided into two subspecies. Although morphological and genetic characters are useful in differentiating among the three species and the two subspecies, respectively, only hydrocarbon analysis can enable differentiation both among the three species and the two subspecies. Due to the limitations of hydrocarbon analysis, such as the need for fresh specimens, alternative methods that could rapidly and accurately identify Zootermopsis would be useful. Using a partial least squares analysis of near-infrared spectra, each of the Zootermopsis species and subspecies were identified with greater than 95% and 80% accuracy, respectively. Neural network analysis of the near-infrared spectra successfully enabled the identification of the species and subspecies with greater than 99% accuracy. The inexpensive, reproducible, and rapid nature of near-infrared spectroscopy makes it a viable alternative to morphological, hydrocarbon, or genetic analysis for identifying Zootermopsis.

External surface disinfection of the lesser mealworm (Coleoptera: Tenebrionidae)

Understanding the dynamics of movement of bacteria within the environment and between species is crucial to unraveling the epidemiology of bacterial diseases and to developing biosecurity measures to prevent dissemination. Many arthropods, some beneficial and some detrimental, inhabit poultry houses. The lesser mealworm, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae), is a pest commonly found in poultry litter that can harbor pathogens involved in both human and animal health issues. Current farm management practices perpetuate persistent infestations contributing to the dispersal of beetles and pathogens. To study the dissemination of bacteria by this beetle, we require the ability to differentiate internal from external sources of bacteria carried by the beetle. In this study, we tested previously described methods to externally disinfect beetles and found disinfectant efficacies between 40 and 98%. The irregular surface of the insect posed a challenge to cleansing procedures because the surface offered many recesses able to sequester bacteria. Complete bacterial disinfection was achieved with a serial treatment of ethanol and hydrogen peroxide or hydrogen peroxide/peracetic acid.

Characterization of a female-produced courtship pheromone in the parasitoid Nasonia vitripennis

Males of the parasitoid Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) show a characteristic courtship behavior. We demonstrate that male arrestment and key behavioral elements of the courtship sequence are mediated by a female-derived contact sex pheromone. Males were arrested on paper disks treated with female extracts but not on those treated with male extracts. Male responsiveness was influenced by the surface to which female extracts were applied. Extracts applied to an extracted beetle elytron arrested males more strongly than those applied to filter paper of comparable size. However, more complex behavioral elements, such as head nodding and copulation attempts, were shown only when extracts were applied to extracted male cadavers, suggesting that tactile or visual cues synergize the male response. The chemicals involved are stable, of low volatility, and nonpolar. Dead females arrested males and elicited courtship behavior for at least 8 d. Males showed no sign of attraction to live females at a distance of 3 cm in an olfactometer. Fractionation of female extracts demonstrated that the activity was exclusively located in the nonpolar fraction. Analysis of the active fraction by gas chromatography-mass spectrometry revealed that cuticular hydrocarbons with chain lengths between 25 and 37 carbon units were present. Comparison of hydrocarbon profiles from males and females showed qualitative and quantitative differences. These results suggest that sex-specific cuticular hydrocarbons are the key signals mediating the male courtship behavior in N. vitripennis.

Tracing pollinator footprints on natural flowers

Many insects are known to leave lipid footprints while walking on smooth surfaces. Presumably, the deposited substances improve tarsal adhesion. In bumblebees, footprint hydrocarbons also function as scent marks that allow detection and avoidance of recently depleted flowers. I used GC-MS to detect hydrocarbons deposited by bumblebee (Bombus pascuorum) on flowers of Lamium maculatum. In addition to the plants' own cuticular lipids, extracts of corollas that had been visited by bumblebees contained odd-numbered alkenes. The amount of pentacosenes (C25H50) on corollas was linearly related to the number of bumblebee visits, with workers depositing approximately 16 ng per visit (extrapolated to a total of 65 ng of bumblebee cuticular hydrocarbons). Pentacosenes were retained on visited flowers without loss for 2 hr, and probably longer. This and results from flight cage experiments suggest that flower epicuticles retain a chemical record of pollinator visitation, including information on visiting bee species. Continuous footprint accumulation necessitates new explanations concerning the reversibility of "repellent scent marks" of bumblebees.

Analysis of Insect Cuticular Hydrocarbons Using Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

Insect cuticular hydrocarbons (CHCs) were probed by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry with a lithium 2,5-dihydroxybenzoate matrix. CHC profiles were obtained for 12 species of diverse insect taxa (termites, ants, a cockroach, and a flesh fly). MALDI spectra revealed the presence of high molecular weight CHCs on the insect cuticle. Hydrocarbons with more than 70 carbon atoms, both saturated and unsaturated, were detected. When compared with gas chromatography/mass spectrometry (GC/MS), MALDI-TOF covered a wider range of CHCs and enabled CHCs of considerably higher molecular weight to be detected. Good congruity between GC/MS and MALDI-TOF was observed in the overlapping region of molecular weights. Moreover, a number of previously undiscovered hydrocarbons were detected in the high mass range beyond the analytical capabilities of current GC/MS instruments. MALDI was shown to hold potential to become an alternative analytical method for insect CHC analyses. The ability of MALDI to discriminate among species varying in the degree of their relatedness was found to be similar to GC/MS. However, neither MALDI-MS nor GC/MS data were able to describe the phylogenetic relationships.

Oxygen and water flux across eggshells ofManduca sexta

Insect eggs must obtain oxygen across the eggshell to support embryonic development. Because eggs are small, obtaining enough oxygen would seem trivial. Recent work, however, has shown that eggs of a moth, Manduca sexta, are oxygen limited at high but realistic temperatures(32–37°C) and that PO2 drops steeply across the eggshell. Here we use theoretical and experimental approaches to partition the total resistance to oxygen flux among several steps in the oxygen cascade from environment to embryo. Standard mass-transfer analysis suggests that boundary layers of air around eggs, and around substrates to which they are attached, offer negligible resistance. Likewise, a mathematical model, parameterized using published and newly obtained morphological data,predicts that air-filled parts of the chorion also do not resist oxygen flux. This prediction was confirmed by experiments that measured rates of carbon dioxide emission from batches of eggs subjected simultaneously to hypoxia and inert gas substitution: depression of metabolic rate by hypoxia was not rescued when the diffusion coefficient of oxygen in air was doubled by substituting helium for nitrogen. The model did predict, however, that a set of subchoral layers (a crystalline chorionic layer, a wax layer and the vitelline membrane) could account for most or all of the total resistance to oxygen flux. Support for this prediction was obtained from two sequential experiments. First, eggs extracted with chloroform:methanol had highly elevated rates of water loss, suggesting that indeed eggs of M. sextaare waterproofed by wax. Second, rates of water loss and carbon dioxide emission from batches of eggs, measured from laying to hatching, changed in parallel over development. These data suggest that a single layer, likely a wax layer or a combination of wax and other subchoral layers, provides the main resistance to water efflux and oxygen influx.

Stage-specific surface chemicals of Plodia interpunctella: 2-acyl-1,3-cyclohexanediones from larval mandibular glands serve as cuticular lipids

Cuticular lipid compositions of all life stages of the stored product moth Plodia interpunctella have been determined. Eggs and adults of P. interpunctella have cuticular lipids consisting solely of hydrocarbons. The composition of eggs and adult females is qualitatively nearly identical with ca. 86 hydrocarbons (11 n-alkanes, 39 monomethyl alkanes, 19 dimethyl alkanes, 11 trimethyl alkanes and 6 monoenes) except females lack the 2-methyl alkanes found in eggs. Adult males have a hydrocarbon composition qualitatively nearly identical to females with the exception that they lack the monoenes. Larval and pupal cuticular lipids are dominated by a mixture of ca. 20 previously described 2-acyl-1,3-cyclohexanediones, with only minute amounts of n-alkanes on the larvae and pupae. The 2-acyl-1,3-cyclohexanediones are continuously secreted onto their silk webbing and food particles by the paired mandibular glands found in all larvae. Extracts from dissected mandibular glands have a qualitatively identical composition to larval cuticular extracts. The pupal stage (which does not have mandibular glands) is enclosed in a silk cocoon also coated with 2-acyl-1,3-cyclohexanediones laid down while the wandering stage larvae spin the cocoon. The 2-acyl-1,3-cyclohexanediones have physical properties which closely mimic those of cuticular hydrocarbons, including melting point and boiling point range and hydrophobicity. This is the first report of an insect with a life stage that does not use conventional cuticular lipids for conservation of water.

Composition of the surface hydrocarbons from the vitelline membranes of dipteran embryos

Hydrocarbons were the major lipid class extracted by hexane from the vitelline membrane surface of dechorionated eggs of the house fly, Musca domestica, the New World screwworm, Cochliomyia hominivorax, the secondary screwworm, Cochliomyia macellaria, the green bottle fly, Phaenicia sericata, the sheep blow fly, Lucilia cuprina and the Mexican fruit fly, Anastrepha ludens. The length of time the embryos must be exposed to hexane with or without a small amount of alcohol in order to attain permeability was species-dependant. Long-chain n-alkanes comprised the major lipid class removed from vitelline membranes of all species except A. ludens where 2-methylalkanes were the major class. The range in size by the total number of carbon atoms in the hydrocarbons was: C23-C49 in C. hominivorax, C27-C33 in C. macellaria, C24-C35 in L. cuprina, C25-C36 in M. domestica, C25-C33 in P. sericata and C21-C51 in A. ludens. The major hydrocarbon component, expressed as percent of the total hydrocarbons, was n-nonacosane (C29) in C. hominivorax (40%), C. macellaria (43%), L. cuprina (38%), M. domestica (39%) and P. sericata (60%). However, in A. ludens, 2-methyloctacosane (32%) was the major hydrocarbon. Unsaturated hydrocarbons, monoenes (16%) and dienes (11%), were abundant only in A. ludens. Since prior studies indicated that the length of time the embryos must be exposed to hexane with or without a small amount of alcohol in order to attain permeability is species dependant, we suggest that the differences in hydrocarbon composition may contribute to this variation in lipid extractability.

Surface hydrocarbons of queen eggs regulate worker reproduction in a social insect

A hitherto largely unresolved problem in behavioral biology is how workers are prevented from reproducing in large insect societies with high relatedness. Signals of the queen are assumed to inform the nestmates about her presence in the colony, which leads to indirect fitness benefits for workers. In the ant Camponotus floridanus, we found such a signal located on queen-laid eggs. In groups of workers that were regularly provided with queen-laid eggs, larvae, and cocoons, with larvae and cocoons alone, or with no brood, only in the groups with queen-laid eggs did workers not lay eggs. Thus, the eggs seem to inform the nestmates about the queen's presence, which induces workers to refrain from reproducing. The signal on queen-laid eggs is presumably the same that enables workers to distinguish between queen- and worker-laid eggs. Despite their viability, the latter are destroyed by workers when given a choice between both types. Queen- and worker-laid eggs differ in their surface hydrocarbons in a way similar to the way fertile queens differ from workers in the composition of their cuticular hydrocarbons. When we transferred hydrocarbons from the queen cuticle to worker-laid eggs, the destruction of those eggs was significantly mitigated. We conclude that queen-derived hydrocarbon labels inform workers about the presence of a fertile queen and thereby regulate worker reproduction.

Ecological adaptation during incipient speciation revealed by precise gene replacement

To understand the role of adaptation in speciation, one must characterize the ecologically relevant phenotypic effects of naturally occurring alleles at loci potentially causing reproductive isolation. The desaturase2 gene of Drosophila melanogaster is such a locus. Two geographically differentiated ds2 alleles underlie a pheromonal difference between the Zimbabwe and Cosmopolitan races. We used a site-directed gene replacement technique to introduce an allele of ds2 from the Zimbabwe population into Cosmopolitan flies. We show that the Cosmopolitan allele confers resistance to cold as well as susceptibility to starvation when the entire genetic background is otherwise identical. We conclude that ecological adaptation likely accompanies sexual isolation between the two behavioral races of D. melanogaster.

Hydrocarbons in the surface wax of eggs and adults of the Colorado potato beetle, Leptinotarsa decemlineata

The major components of the egg hydrocarbons were dimethylalkanes (40%) and trimethylalkanes (24%) in which the first methyl branch was on carbon 2. The major dimethylalkanes were an approximately 2:1 mixture of 2,10- and 2,6-dimethyloctacosanes in females and eggs. The major trimethylalkanes were a mixture of 2,10,16- and 2,10,18-trimethyloctacosanes. 2,x- and 2,x,y-methyl-branched alkanes with an odd-numbered carbon backbone were proposed to have an even number of carbon atoms between the first and second methyl branch points indicating that their biosynthesis started with a primer derived from leucine. 13,17,21,25-Tetramethylheptatriacontane was the only tetramethylalkane identified. Females and eggs had more hydrocarbons with a 2-methyl branch point than did the males. The eggs had the lowest amount of internally-branched dimethylalkanes but the largest amount of 2,x-dimethylalkanes in their surface hydrocarbons. Only trace amounts of n-alkanes and alkenes were detected in the surface hydrocarbons of adult males and females, larvae and eggs, of the Colorado potato beetle.

A nonspecific fatty acid within the bumblebee mating plug prevents females from remating

The best mating strategy for males differs from that of females, because females gain from mating with several males (polyandry), but males gain from monopolizing the females. As a consequence, males have evolved a variety of methods, such as the transfer of inhibitory substances from their accessory glands, to ensure exclusive paternity of the female's offspring, generally with detrimental effects on female fitness. Inhibitory substances have been identified as peptides or other specific molecules. Unfortunately, in social insects male-mating traits are investigated only poorly, although male social insects might have the same fundamental influence on female-mating behavior as found in other species. A recently developed technique for the artificial insemination of bumblebee queens allowed us to investigate which chemical compound in the mating plug of male bumblebees, Bombus terrestris L., prevents females (queens) from further mating. Surprisingly, we found that the active substance is linoleic acid, a ubiquitous and rather unspecific fatty acid. Contrary to mating plugs in other insect species, the bumblebee mating plug is highly efficient and allows the males to determine queen-mating frequencies.

Modification of morphological characters and cuticular compounds in worker ants Leptothorax nylanderi induced by endoparasites Anomotaenia brevis

Anomotaenia brevis (Cestoda, Cyclophyllidea) induces major changes in the morphological characters of the host ant, Leptothorax nylanderi (Hymenoptera, Formicidae): alteration of pigmentation, lowering of adult mean size, reduction of legs, eyes and head, enlargement of petiole. The presence of parasites in adult ants also modifies the quantity of cuticular compounds but not their quality. The parasite induces some changes in the synthesis/release of 13 cuticular hydrocarbons. The higher the number of parasites within a worker, the larger the quantitative changes in four cuticular hydrocarbons in comparison with normal ants. Such modifications (morphology, chemistry, behaviour) may explain the partial intolerance exerted by normal workers against the parasitized ants.

A Chemotaxonomic Study of Cuticular Hydrocarbons on Epilachna indica (Family: Coccinellidae) from Sarawak

The chemical composition of cuticular hydrocarbons of adult Epilacnha indica (ladybird beetles), collected fromKota Samarahan, Kota Padawan and Lanjak-Entimau, Sarawak were analyzed by using a capillary gaschromatography-mass spectrometer (GC-MS). Cuticular hydrocarbons extracted from 18 samples of adult E.indica (comprise of 90 individuals). Over 95% of the hydrocarbon peak areas consist of chain lengths from C18to C38 . The proportions of n-alkanes between three different localities are significantly difference, except for ndotriacontaneand n-tetratriacontane. Comparison between Kota Samarahan and Kota Padawan samples revealedthe significant different in hydrocarbon composition for even-numbered carbon n-alkanes ranging from n-C18 ton-C38 except for n-C32 and n-C34 . Several odd-numbered carbon n-alkanes such as n-C25 , n-C27 , n-C33 and n-C35 also showed significant difference in the composition between Kota Samarahan and Kota Padawan.Examination on components contributing to the differentiation of localities showed that n-C29 , n-C33 and n-C36were important in discriminating three different localities. Discriminant function analysis (DFA) successfullyclassified all samples into three correct groups in 100% of cases, with cross-validation resulted in an error of7.7%. Individuals from each locality were grouped in the range of 2.10 - 9.16% differences, with average of43% different reflected between localities. E. indica samples collected from the forests containing simplerhydrocarbon pattern than samples collected around housing or industrial areas. Result showed that differences inmicroenvironment have influenced the composition and proportion of insect cuticular hydrocarbon. The findingreveals the potential of cuticular hydrocarbons profile to separate subpopulations of species.