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 p est control against the American serpentine leaf miner Liriomyza trifo lii Burgess. We studied the parasitoid's host searching behavior, usin g olfactometric methods. Our data show that the parasitoids locate hos t larvae (a leaf-mining dipteran) on the basis of volatile signals rel eased by the plant-host complex. Female D. isaea are strongly attracte d to the odors arising from damaged bean plants, whereas they show pra ctically no response to intact plants. The results of our chemical ana lyses 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 signi ficantly 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 amount s of these substances, which probably lead the parasites to their host s. The compounds thus act as synomones.