Pheromone communication among sexes of the garden cross spider Araneus diadematus

Chemical communication plays a fundamental role in many aspects of an animal’s life from assessing habitat quality to finding mating partners. Behavioural observations show that chemical communication likewise plays an important role in spiders, but the contexts and the substances involved are little explored. Here, we investigate the chemical communication in the garden cross spider Araneus diadematus (Clerck, 1757) between and within the sexes. Using choice trials, we demonstrate that males are attracted to odours of adult females, but not to those of subadult females. Our data further suggest that adult females avoid odours of conspecific adult females, possibly in order to reduce reproductive competition with other females. Cuticle and silk extracts as well as headspace samples of subadult and adult virgin females were analysed via GC–MS. Available candidate compounds for the female sex pheromone were tested via electroantennography on palps (electropalpography) of adult virgin females and on females in behavioural trials. We propose sulcatone (6-methyl-5-hepten-2-one) as a candidate substance for the female volatile pheromone and several long-chained alkanes and alcohols as candidates for contact pheromones. Apart from demonstrating that attraction of males to females depends on the latter’s developmental stage, our study suggests that pheromones can also play an important role between females, an aspect that requires further attention.

Linear Alkanes and Reproductive Status of Polistes versicolor (Hymenoptera: Vespidae) Females in Winter Aggregates

Female wasps such as Polistes versicolor can form aggregates to face weather conditions that are not suitable to sustain their colonies. The interactions between individuals in these aggregates, just as in other associations, are probably facilitated by chemical signals. Of these compounds some of the most efficient during social interactions of insects are those called contact pheromones or superficial pheromones. This special type of pheromones, known as cuticular hydrocarbons, can be found in insects cuticle. They facilitate the differentiation of caste, species and nestmates, and may be important indicators of dominance as well as fertility. Some studies indicate that linear alkanes are important cuticular compounds for intraspecific recognition and discrimination. The aim of this study was to evaluate the relationship between reproductive physiologic condition and the linear alkanes present in the cuticle of females of P. versicolor in aggregates employing Gas Chromatography with Flame Ionization Detector (GC-FID). Females from distinct aggregates were differentiated by the chemical composition of their cuticle. In each aggregate, there was difference in cuticular chemical composition between females with different ovarian development degrees, allowing the distinction between inseminated and non-inseminated females.

Isolation and determination of absolute configurations of insect-produced methyl-branched hydrocarbons

Although the effects of stereochemistry have been studied extensively for volatile insect pheromones, little is known about the effects of chirality in the nonvolatile methyl-branched hydrocarbons (MBCHs) used by many insects as contact pheromones. MBCHs generally contain one or more chiral centers and so two or more stereoisomeric forms are possible for each structure. However, it is not known whether insects biosynthesize these molecules in high stereoisomeric purity, nor is it known whether insects can distinguish the different stereoisomeric forms of MBCHs. This knowledge gap is due in part to the lack of methods for isolating individual MBCHs from the complex cuticular hydrocarbon (CHC) blends of insects, as well as the difficulty in determining the absolute configurations of the isolated MBCHs. To address these deficiencies, we report a straightforward method for the isolation of individual cuticular hydrocarbons from the complex CHC blend. The method was used to isolate 36 pure MBCHs from 20 species in nine insect orders. The absolute stereochemistries of the purified MBCHs then were determined by digital polarimetry. The absolute configurations of all of the isolated MBCHs were determined to be (R) by comparison with a library of synthesized, enantiomerically pure standards, suggesting that the biosynthetic pathways used to construct MBCHs are highly conserved within the Insecta. The development of a straightforward method for isolation of specific CHCs will enable determination of their functional roles by providing pure compounds for bioassays.

The effect of sex and maturation on cuticular semiochemicals in Monochamus scutellatus (Coleoptera: Cerambycidae)

Contact pheromones are a subset of a complex mixture of hydrocarbons secreted on the cuticle and play an important role in the mating behaviour of several cerambycid species (Coleoptera: Cerambycidae). In this study, we investigated the relationship between maturation (newly eclosed and sexually mature) adult Monochamus scutellatus (Say) beetles and sex and the composition of the cuticular hydrocarbon blend to determine if this information is encoded in the blend and potentially available for communication purposes. Whole-body extracts of unfed females, and both mature females and males were analysed by gas chromatography mass spectrometry to identify and quantify the components of the cuticular hydrocarbons. There were no unique compounds present in any of the three groups, but discriminant analysis indicated that the relative proportions of the cuticular hydrocarbon components were unique for each group.