Role of plant volatiles in the search for a host by parasitoid Diglyphus isaea (Hymenoptera: Eulophidae)

Diglyphus isaea Walker is a larval ectoparasitoid used in biological pest control against the American serpentine leaf miner Liriomyza trifolii Burgess. We studied the parasitoid's host searching behavior, using olfactometric methods. Our data show that the parasitoids locate host larvae (a leaf-mining dipteran) on the basis of volatile signals released by the plant-host complex. Female D. isaea are strongly attracted to the odors arising from damaged bean plants, whereas they show practically no response to intact plants. The results of our chemical analyses showed that about 15 components were present, two of which, cis-3-hexen-1-ol and 4-hydroxy-4-methyl-2-pentanone, were present in significantly larger quantities in the leaf extracts from mined or damaged bean plants than in those from healthy plants. The damage inflicted by the host larvae on these plants triggers the release of larger amounts of these substances, which probably lead the parasites to their hosts. The compounds thus act as synomones.