Components of the sex pheromone of blackcurrant sawfly, Nematus olfaciens (Hymenoptera: Tenthredinidae): novel isopropyl esters and the role of hydrocarbons
Abstract: Blackcurrant sawfly, Nematus olfaciens (Hymenoptera: Tenthredinidae), is a common and frequently damaging pest of blackcurrant, probably present to varying degrees in all UK blackcurrant plantations. Infestation is sporadic and localised, and damage can occur rapidly. No practical, systematic sampling methods or attendant crop damage thresholds have been developed, and pheromone traps could provide such a tool. Previous work on related sawfly species has suggested that breakdown products of cuticular hydrocarbons act as components of the female sex pheromone. We found that male and female blackcurrant sawfly produce large quantities of identical suites of long-chain saturated and unsaturated hydrocarbons, of which (Z)-9-tricosene is the most abundant. Analysis of collections of volatiles from virgin females by gas chromatography linked to electroantennographic (EAG) recording from the antennae of males showed no EAG responses to the hydrocarbons but very strong responses to at least three compounds present in trace quantities. These were identified as mono-unsaturated isopropyl esters, including the (Z)-5-tetradecenoate, (Z)-7-tetradecenoate and (Z)-7-hexadecenoate. The synthetic compounds elicited strong EAG responses from male blackcurrant sawfly and no EAG responses were observed to likely breakdown products of the unsaturated hydrocarbons. In field tests, blends of the isopropyl esters attracted male blackcurrant sawfly and addition of (Z)-9-tricosene further increased the attractiveness. These results suggest a role for cuticular hydrocarbons that is somewhat different from that proposed for related sawfly species.