Ontogenetic, reproductive, and nutritional effects on the cuticular hydrocarbons of the host-specific ectoparasitoid Cephalonomia tarsalis (Hymenoptera: Bethylidae)

Abstract

Cuticular hydrocarbons have been identified from adult males and females of the bethylid wasp Cephalonomia tarsalis (Ashmead). The 2 sexes possess the same cuticular hydrocarbons, but in different amounts and proportions. Hydrocarbon components identified include n-alkanes (C23-C37), 5-methyl alkanes (5-MeC25-SMeC29), 5,X-dimethyl alkanes (5,17-and 5,19-diMeC29 and 5,17- and 5,19-diMeC33), and a homologous series of Z-monones with double bonds at Δ11, Δ9, and Δ7 (C25:1-C37:1). The n-alkanes and alkenes are the predominant components in all cases, the 5-methyl alkanes being only minor components. The dimethyl components are present in only trace amounts. Age, mating status, and, for females, host-feeding status, were examined for their effect on hydrocarbon quantities and proportions. Males showed little change in their hydrocarbon profiles, but females showed strong age, host feeding, and age × host feeding effects on total hydrocarbon quantities and on individual hydrocarbon components. Mating status did not affect female hydrocarbons. The silk cocoons from which the parasites emerged yielded the same cuticular hydrocarbon components as were found on the newly emerged male and female wasps, but n-alkanes were now the major components. Hydrocarbon profiles of female cocoons differed from male cocoon hydrocarbons primarily in the relative abundances of the monene isomers. Bioassays of male response to hexane extracts of female and male cocoons indicated that the male could differentiate between the two. The primary gender recognition cue is not the cocoon hydrocarbons, but rather a female-produced sex pheromone, the hydrocarbons serving as a secondary recognition cue.