Origin and identification of bacteria which produce kairomones in the frass ofAcrolepiopsis assectella (Lep., Hyponomeutoidea)

The volatiles used by the parasitoidDiadromus pulchellus to find its host, the leek moth, are produced by the bacteria developing in the frass of the host larvae. The origin and the nature of these bacteria were investigated. Samples were taken from healthy leeks and from infested leeks in the field, as well as from the frass of larvae reared in the laboratory either on the host plant or on an artificial diet. The various species of bacteria identified were cultured in the presence of precursors of leek sulphur volatiles and their volatile emissions were analysed.Klebsiella oxytoca and variousBacillus, common decomposers of plant matter, were the principal species producing active volatiles which were alkyl disulphides.