Cuticular hydrocarbons as contact sex pheromone in the parasitoid Dibrachys cavus

Cuticular hydrocarbons (CHCs) cover the cuticle of virtually any insect and do not only protect them from desiccation, but also possess various communicative functions. Previous studies suggested a function as contact sex pheromones in the parasitic wasp family Pteromalidae, but further species need to be studied before more general conclusions are possible. Here, we demonstrate a contact sex pheromone in females of Dibrachys cavus (Walker) (Hymenoptera: Pteromalidae). Males of this parasitoid were arrested on cadavers of 1- to 2-day-old females, but neither on newly emerged females nor on males. Extracts from 1- to 2-day-old females and non-polar fractions were also behaviorally active suggesting a non-polar contact sex pheromone. Chemical analyses of bioactive and non-active CHC profiles by gas chromatography-mass spectrometry and subsequent principal component analysis (PCA) revealed that the bioactive profiles from 1- to 2-day-old females were clearly distinguishable from all other profiles. Among the chemicals showing the strongest impact in the PCA were the two 3-methylalkanes 3-methylnonacosane and 3-methylhentriacontane, which were absent or trace components in the inactive profiles and whose relative amounts increased in females when they became sexually attractive. The putative function of 3-methylalkanes as key components of the contact sex pheromones in Pteromalidae is discussed.