Pheromonal secretions from glands on the 5th abdominal sternite of hydropsychid and rhyacophilid caddisflies (Trichoptera)

Extracts of different body parts of adult Trichoptera were tested for electrophysiological activity. Extracts of the IVth and Vth abdominal sternites of female Hydropsyche angustipennis, Rhyacophila nubila, and R. fasciata, containing a paired exocrine gland, elicited significant electroantennographic responses when tested on conspecific male antennae. The paired gland occurs also in males of all the species, and in H. angustipennis, extracts from males were more active than female extracts when tested on male antennae. Female and male extracts from all species were analyzed by gas chromatography with simultaneous flame ionization and electroantennographic detection (EAD). EAD-active peaks in female extracts, stimulating male antennae, were identified in H. angustipennis as nonan-2-one; and in R. nubila and R. fasciata as heptan-2-one, heptan-2-ol, nonan-2-one, and nonan-2-ol. EAD-active components from male H. angustipennis stimulating male antennae were octan-2-one, nonan-2-one (major peak), (Z)-6-nonen-2-one, decanone. 2-and a methylbranched decan-2-one. Female extracts and synthetic mixtures of compounds identified from female H. angustipennis and R. fasciata were tested for attractivity in the field. High catches with control traps obscured the results, but a synthetic mixture of the four identified compounds was significantly attractive and not different from female extracts for attracting male R. fasciata. In H. angustipennis, a synthetic six-component male blend, in which nonan-2-one was the major component, attracted significant numbers of male and female H. angustipennis. Extracts of male R. nubila and R. fasciata contained acetophenone and hexanoic and octanoic acids but did not have any electrophysiological or behavioral activity on either male or female antennae of conspecifics. The occurrence of a female sex pheromone in Rhyacophila and an aggregation pheromone in Hydropsyche corresponds to earlier described differences in mating behaviors in the Rhyacophilidae and Hydropsychidae.