Pheromonal basis for aggregation behavior of parasitoids of the gypsy moth:Brachymeria intermedia (Nees) andBrachymeria lasus (Walker) (Hymenoptera: Chalcididae).

The parasitoidsB. intermedia andB. lasus aggregate at sites previously frequented. Extracts from filter paper conditioned by aggregated parasitoids were chromatographed (adsorption column and gas-liquid chromatography) and bioassayed. An active component that elicited aggregation response forB. intermedia was isolated and identified as 3-hexanone. This molecule was found in trace quantities (5-10 ng/female or male) on filter paper conditioned by either male, female or a combination of the sexes.