Claude Everaerts

Drosophila Cuticular Hydrocarbons Revisited: Mating Status Alters Cuticular Profiles

Most living organisms use pheromones for inter-individual communication. In Drosophila melanogaster flies, several pheromones perceived either by contact/at a short distance (cuticular hydrocarbons, CHs), or at a longer distance (cis-vaccenyl acetate, cVA), affect courtship and mating behaviours. However, it has not previously been possible to precisely identify all potential pheromonal compounds and simultaneously monitor their variation on a time scale. To overcome this limitation, we combined Solid Phase Micro-Extraction with gas-chromatography coupled with mass-spectrometry. This allowed us (i) to identify 59 cuticular compounds, including 17 new CHs; (ii) to precisely quantify the amount of each compound that could be detected by another fly, and (iii) to measure the variation of these substances as a function of aging and mating. Sex-specific variation appeared with age, while mating affected cuticular compounds in both sexes with three possible patterns: variation was (i) reciprocal in the two sexes, suggesting a passive mechanical transfer during mating, (ii) parallel in both sexes, such as for cVA which strikingly appeared during mating, or (iii) unilateral, presumably as a result of sexual interaction. We provide a complete reassessment of all Drosophila CHs and suggest that the chemical conversation between male and female flies is far more complex than is generally accepted. We conclude that focusing on individual compounds will not provide a satisfactory understanding of the evolution and function of chemical communication in Drosophila.

An Inhibitory Sex Pheromone Tastes Bitter for Drosophila Males

Sexual behavior requires animals to distinguish between the sexes and to respond appropriately to each of them. In Drosophila melanogaster, as in many insects, cuticular hydrocarbons are thought to be involved in sex recognition and in mating behavior, but there is no direct neuronal evidence of their pheromonal effect. Using behavioral and electrophysiological measures of responses to natural and synthetic compounds, we show that Z-7-tricosene, a Drosophila male cuticular hydrocarbon, acts as a sex pheromone and inhibits male-male courtship. These data provide the first direct demonstration that an insect cuticular hydrocarbon is detected as a sex pheromone. Intriguingly, we show that a particular type of gustatory neurons of the labial palps respond both to Z-7-tricosene and to bitter stimuli. Cross-adaptation between Z-7-tricosene and bitter stimuli further indicates that these two very different substances are processed by the same neural pathways. Furthermore, the two substances induced similar behavioral responses both in courtship and feeding tests. We conclude that the inhibitory pheromone tastes bitter to the fly.

Postembryonic Development of Zophobas atratus Fab. (Coleoptera: Tenebrionidae) under Crowded or Isolated Conditions and Effects of Juvenile Hormone Analogue Applications

Abstract Pupation in Zophobas atratus is dependent on isolation and this provides a model for study of the onset of metamorphosis in beetles. We have analyzed the effects of isolation vs grouping on certain developmental parameters; the number of larval instars; their duration and weight. Sex differences were detected, such as the occurrence of regressive moults in females. Moreover, the development of Z. atratus is discussed in relation to Tenebrio molitor , the physiological timing of which appeared in part extendable to Z. atratus . Experiments show that 4–6 days of isolation are required for commencement of metamorphosis, as indicated by an immobile crooked posture observed at the end of this period, characterizing the beginning of prepupal development. During this period, return to grouped conditions, as well as applications of a juvenile hormone analogue (ZR 515) prevented metamorphosis and precipitated another larval moult. This suggests that grouped conditions may delay the onset of metamorphosis through the modulation of juvenile hormone titres.

Effects of juvenile hormone analogues upon soldier differentiation in the termite Reticulitermes santonensis (Rhinotermitidae, Heterotermitinae)

Under the influence of juvenile hormone analogues (JHAs), termite workers are induced to differentiate into soldiers. In Reticulitermes santonensis, such induced differentiation is often incomplete, resulting in intercaste production. The morphology of the structures most affected during differentiation was analyzed descriptively and biometrically in normal workers, presoldiers, and soldiers, and in experimental intercastes. We observed that intercastes form a morphological and biometrical continuum between workers and presoldiers (presoldier intercastes), and between presoldiers and soldiers (soldier intercastes). We also compared the biochemistry of the normal individuals and of the intercastes; in contrast to workers, the intercastes possess a frontal gland secretion which differs from those of the presoldiers and soldiers. Besides intercaste characterization, we consider the mode of action of JHAs in termite differentiation.

Fatty-Acid Preference Changes during Development in Drosophila melanogaster

Fatty-acids (FAs) are required in the diet of many animals throughout their life. However, the mechanisms involved in the perception of and preferences for dietary saturated and unsaturated FAs (SFAs and UFAs, respectively) remain poorly explored, especially in insects. Using the model species Drosophila melanogaster, we measured the responses of wild-type larvae and adults to pure SFAs (14, 16, and 18 carbons) and UFAs (C18 with 1, 2, or 3 double-bonds). Individual and group behavioral tests revealed different preferences in larvae and adults. Larvae preferred UFAs whereas SFAs tended to induce both a strong aversion and a persistent aggregation behavior. Adults generally preferred SFAs, and laid more eggs and had a longer life span when ingesting these substances as compared to UFAs. Our data suggest that insects can discriminate long-chain dietary FAs. The developmental change in preference shown by this species might reflect functional variation in use of FAs or stage-specific nutritional requirements, and may be fundamental for insect use of these major dietary components.

(+)-α-Pinene in the defensive secretion of Nasutitermes princeps (Isoptera, Termitidae)

The frontal secretion ofNasutitermes princeps consists of 89% diterpenes and 11% monoterpenes. In the samples studied, (+)-α-pinene, whose optical purity reaches 99.5%, accounts for more than 80% of the monoterpenic content.

Is mate choice in Drosophila males guided by olfactory or gustatory pheromones

Drosophila melanogaster flies use both olfactory and taste systems to detect sex pheromones and select the most suitable mate for reproduction. In nature, flies often face multiple potential partners and should have an acute sensory ability to discriminate between different pheromonal bouquets. We investigated both the pheromones and the chemosensory neurons influencing Drosophila mate choice. We measured various courtship traits in single tester males simultaneously presented with two target male and/or female flies carrying different pheromonal bouquets (pairs of control flies of the same or different sex, same-sex target pairs of pheromonal variant strains). The courtship traits reflected the perception of either olfactory cues perceived before or gustatory cues perceived after the first physical taste contact. Our results suggest that male mate choice exists in D. melanogaster and that male discrimination between potential mates could be a two-step process involving chemical cues perceived before and after the first gustatory contact. In addition, when a male was simultaneously presented with two potential sexual partners, the olfactory and gustatory cues he used depended on the pheromonal patterns of both flies, but his response could also depend on additional effects resulting from the simultaneous perception of the two flies, leading to a nonlinear choice of a sexual partner. Moreover, some tester males with genetically altered gustatory receptor neurons strongly changed their partner preference, indicating that the flys peripheral nervous system is essential for pheromonal detection and mate choice.

The monoterpenoid fraction of the defensive secretion in Nasutitermitinae from Papua New Guinea

Abstract The composition of the monoterpenoid fraction of the defensive frontal secretion is elucidated in eight Nasutitermitinae species, namely: Grallatotermes grallator, Nasutitermes gracilirostris, N. novarumhebridarum, N. polygynus, N. princeps, N. rufirostris and two undescribed Nasutiterrnes . Each species possesses a characteristic blend of rnonoterpenes. α Pinene predominates in the secretion of four species from these. The other important monoterpenes are β-pinene, limonene and myrcene. Sabinene is present in the secretion of G. grallator, N. gracilirostris, N. princeps and one species from the undescribed Nasutitermes . It is the first time that sabinene is detected in Nasutitaermes and Grallototermes frontal secretion. Another monoterpene undescribed in Nasutitermitinae defensive secretion was identified in N . sp. F as ( R )-cyclohexene, l -methyl-5-(1-methylethenyl).

The Cryptocercus punctulatus species complex (Dictyoptera: Cryptocercidae) in the eastern United States: comparison of cuticular hydrocarbons, chromosome number, and DNA sequences.

The goal of the current study was to determine if cuticular hydrocarbons could be used to empirically delimit taxa within the Cryptocercus punctulatus species complex in the eastern United States. Cockroaches were collected from rotting logs in 22 locations across four states. Hydrocarbon phenotypes and two mitochondrial (16S and COII) genes and one nuclear (ITS2) gene were independently analyzed to determine their relationship with chromosome number. Five distinct hydrocarbon phenotypes were found, but these were only partly congruent with chromosome number and thus with purported species descriptions. Molecular and cuticular hydrocarbon data each indicate that Cryptocercus with a male karyotype of 2n=43 belong to at least two distinct, distantly related lineages. One 2n=43 lineage is sister group to the 2n=37 and 2n=39 clade, and has a unique hydrocarbon profile. The other 2n=43 lineage is sister group to the 2n=45 samples, and its cuticular hydrocarbons group with four samples of the 2n=45 lineage. The cuticular hydrocarbons of two additional 2n=45 samples diverge from this assemblage. Results indicate cuticular hydrocarbons and chromosome number have some degree of evolutionary independence; neither is completely reliable in delineating historical lineages. Our data provide support for the parallel model of chromosome evolution in the species complex.

Defensive secretions of nymphs and adults of five species of Pyrrhocoridae (Insecta: Heteroptera)

Abstract The chemical composition of the defensive secretions of the nymphs and the adults of Dysdercus fasciatus was investigated. Thirty compounds were identified from the nymphal posterior dorsoabdominal glands, and 34 from the adult metathoracic glands of both sexes. The data were compared with those reported for other species of Pyrrhocoridae. For the species Dysdercus cingulatus, D. fasciatus , and Pyrrhocoris apertus , 63 identified compounds can be divided into 11 chemical groups: aldehydes, saturated hydrocarbons, acetates, alcohols, terpenes, lactones, ketones, esters, alkenes, acids and miscellaneous compounds. These data and those from the literature on Dysdercus intermedius and Dysdercus supersitiosus were analysed by an Euclidian distance clustering which emphasized the differences between nymphal and adult secretions. D. fasciatus is the only species which displays a sexual dimorphism in the composition of the secretion of the metathoracic glands.