Chemicals used for host recognition by the granary weevil parasitoid Lariophagus distinguendus

In order to develop methods for mass rearing of the parasitic wasp Lariopha gus distinguendus, we characterized and identified chemicals used by this p arasitoid to recognize wheat grains infested by its host, larvae of the gra nary weevil, Sitophilus granarius, a major pest of stored grain worldwide. Bioassays revealed that drumming and drilling behavior of the parasitoids o n grain models of filter paper treated with host frets was as intense as on host-infested grains. Thus. chemicals from feces are highly important to r ecognize infested grains. Extracts of the feces with hexane or dichlorometh ane applied on grain models were able to provoke drumming and drilling acti vity. Hexane extract of feces was as active as infested grain itself Subseq uent fractionation of the hexane extract by adsorption chromatography revea led that highest activity was recovered in the dichloromethane fraction. Th is fraction was characterized by the presence of alpha -tocopherol, beta -t ocopherol, beta -tocotrienol, cholesterol, ergostenol, and beta -sitosterol . Synthetic chemicals in proportions found in the active dichloromethane fr action stimulated drumming behavior in bioassays. The significance of these results with respect to the mass propagation of L. distinguendus as natura l enemies for the control of the granary weevil is discussed.