ELECTROPHYSIOLOGICAL AND BEHAVIORAL EVIDENCE FOR A 4TH SEX-PHEROMONE COMPONENT IN THE TURNIP MOTH, AGROTIS-SEGETUM

In addition to the pheromone components (Z)-5-decenyl, (Z)-7-dodecenyl and (Z)-9-tetradecenyl acetate (Z5-10:OAc, Z7-12:OAc and Z9-14:OAc), it has previously been shown that the sex pheromone gland of the turni p moth, Agrotis segetum (Lepidoptera: Noctuidae Schiff) contains 10:OA c, 12:OAc, Z5-12:OAc, Z9-12:OAc, 11-12:OAc, Z5-14:OAc, Z7-14:OAc and Z 11-16:OAc. To find out whether any of these additional compounds is in volved in the sex pheromone communication in A. segetum, a comprehensi ve electrophysiological and behavioural investigation was conducted. S ingle-sensillum recordings on male antennae revealed three subtypes of sensilla among the previously so-called Z5-10:OAc sensilla. One subty pe was identified having one receptor neurone (A) that responded to Z5 -10:OAc with a large spike amplitude and another neurone (B) that resp onded to (Z)-5-decenol (Z5-10:OH) with a small spike amplitude. In ano ther subtype the B neurone responded to Z5-12:OAc and sometimes also t o Z7-12:OAc and 10:OAc, in addition to responding to Z5-10:OH. In a th ird subtype the A neurone responded to all acetates identified from th e female pheromone gland, whereas the small. spike amplitude neurone w as tuned to Z5-10:OH. A flight tunnel assay showed that blends compose d of nine, eight or seven compounds were equivalent to the previously identified three-component pheromone blend in eliciting male behaviour al responses. In field trapping tests, blends of eleven, nine or seven compounds did, however, catch significantly more moths than the three -component blend. Further assays showed that only Z5-12:OAc could sign ificantly increase the catch numbers when added to the three-component blend, and thus qualified as a fourth pheromone component in A. seget um. The behavioural significance of additional female-produced acetate s - for which males possess antennal receptors - is suggested, but may be impossible to confirm because of 'diminishing returns' when trying to refine a multicomponent pheromone further.