(3Z,6Z,9Z,12Z,15Z)-pentacosapentaene and (9Z,11E)-tetradecadienyl acetate: sex pheromone of the spruce coneworm Dioryctria abietella (Lepidoptera: Pyralidae)

The spruce coneworm, Dioryctria abietella Denis & Schiffermüller (Lepidoptera: Pyralidae), is a major pest in spruce seed orchards in Europe. Initial work on its pheromone ecology reported significant attraction of males to (9Z,11E)-tetradecadienyl acetate (9Z,11E-14:OAc), but this compound appeared to be a very weak attractant in field trials. In this study, we show that a second female-produced compound, the polyunsaturated long-chain hydrocarbon (3Z,6Z,9Z,12Z,15Z)-pentacosapentaene (C25 pentaene), is a strong synergist to 9Z,11E-14:OAc, and that both compounds are needed for significant attraction of males. In field-trapping experiments, the highest catches were obtained with high amounts of pentaene added to the acetate (acetate:pentaene ratio from 1 : 10 to 1 : 30) and the highest doses (1–3 mg per rubber septum dispenser) were the most attractive. Two potential behavioural synergists, (Z)-9-tetradecenyl acetate and (9Z,12E)-tetradecadienyl acetate, turned out to be behavioural antagonists and both reduced trap catch of D. abietella in a dose-dependent way when added individually to the binary blend. The recent discovery of the C25 pentaene as a pheromone component of D. abietella, as well as of three North American congeners, suggests that the use of a mixture of so-called type I and type II pheromone compounds is a widespread motif of sexual communication within the genus. The identification of a highly attractive sex pheromone will help in developing efficient strategies for monitoring and control of D. abietella populations in European spruce seed orchards.