Electrophysiological and behavioural responses of Pityophthorus pubescens (Coleoptera: Scolytinae) to (E,E)-α-farnesene, (R)-(+)-limonene and (S)-(-)-verbenone in Pinus radiata (Pinaceae) stands in northern Spain.

Some twig beetles in the genus Pityophthorus (Coleoptera: Scolytinae) may vector pitch canker disease Fusarium circinatum (Niremberg & O'Donnell) of Pinus spp. (Pinaceae). Because Pityophthorus pubescens (Marsh.) has been found to be associated with F. circinatum in the Basque Country (northern Spain), various experiments were conducted to assess the beetle's behavioural responses to (E, E)-α-farnesene, (R)-(+)-limonene and (S)-(-)-verbenone to develop a potential inhibitor to host attraction. These experiments comprise electroantennographic and double-choice olfactometer tests, as well as field assays in Pinus radiata D. Don stands. Both sexes of P. pubescens showed similar electroantennographic responses to different doses (from 1 ng to 1 µg in decadic steps) of each individual compound, with depolarisations to (S)-(-)-verbenone (100 ng) being similar to those of the aggregation pheromone (+)-trans-pityol. In olfactometer assays, both sexes were significantly attracted to (+)-trans-pityol, but the attraction was reduced when increasing amounts of the chemicals were added to the pheromone. Particularly relevant was the repellent effect induced by (S)-(-)-verbenone at 1 ng dose and higher. In the field, (E, E)-α-farnesene, (R)-(+)-limonene and (S)-(-)-verbenone reduced significantly the number of beetles attracted to (+)-trans-pityol and racemic trans-pityol, with (S)-(-)-verbenone being the most effective. (S)-(-)-Verbenone showed an interesting potential for use in the protection of P. radiata stands. A potentially effective strategy, which could be implemented in further, more in-depth studies, could involve the use of this semiochemical as repellent and (+)-trans-pityol-baited traps as attractant in a 'push-pull' strategy.