The role of volatiles from cruciferous plants and pre-flight experience inthe foraging behaviour of the specialist parasitoid Cotesia plutellae

The braconid Cotesia plutellae is an important larval parasitoid of the dia mondback moth (Plutella xylostella), a major pest of crucifers in the tropi cs and sub-tropics. The in-flight searching behaviour of C. plutellae was i nvestigated in a wind tunnel and the close-range attack behaviour observed in cages. The relative importance of volatile stimuli emanating from the pl ant-host-complex, oilseed rape (Brassica napus) - P. xylostella, in the lon g-range attraction of C. plutellae was investigated. Plants that were mecha nically damaged, or damaged by P. xylostella larvae, were attractive to the parasitoid. Host-damaged leaves remained attractive to the parasitoid afte r removal of the host larvae. These results indicate that C. plutellae pred ominantly uses plant derived stimuli in its in-flight searching behaviour. An oviposition experience or contact with a host-damaged leaf prior to the bioassay significantly increased the response to these volatile cues. The f oraging behaviour of C. plutellae is compared with other braconid larval pa rasitoids attacking lepidopteran hosts on crucifers.