Field responses of the Asian larch bark beetle, Ips subelongatus, to potential aggregation pheromone components: disparity between two populations in northeastern China

Abstract Behavioral responses of the Asian larch bark beetle, Ips subelongatus Motsch. to three potential aggregation pheromone components, ipsenol (racemic or [−]-enantiomer), ipsdienol (racemic or [+]-enantiomer) and 3-methyl-3-buten-1-ol, were tested using partial or full factorial experimental designs in two provinces (Inner Mongolia and Jilin) of northeastern China. Our field bioassays in Inner Mongolia (Larix principis-rupprechtii Mayr. plantation) clearly showed that ipsenol, either racemic or 97%-(−)-enantiomer, was the only compound that significantly attracted both sexes of I. subelongatus, while all other compounds (singly or in combinations) were unattractive. There were no two- or three-way synergistic interactions. However, in Jilin Province (L. gmelini[Rupr.] Rupr. Plantation), all the individual compounds tested were inactive, except a very weak activity by 97%-(−)-ipsenol in 2004 when the beetle population was very high. While a combination of ipsenol and ipsdienol (racemates or enantiomerically pure natural enantiomers) showed a significant attraction for both sexes of I. subelongatus, indicating a two-way synergistic interaction between these two major components, addition of 3-methyl-3-buten-1-ol to these active binary blend(s) did not have any effects on trap catches, suggesting that ipsenol and ipsdienol are the synergistic aggregation pheromone components of I. subelongatus in Jilin Province. It seems that 97%-(−)-ipsenol in Inner Mongolia or the binary blend of 97%-(−)-ipsenol and 97%-(+)-ipsdienol in Jilin Province are superior to their corresponding racemates, which might be due either to weak inhibitory effects of the antipode enantiomers or to reduced release rates of the active natural enantiomer(s) in the racemate(s). Our current bioassay results suggest that there is a strong geographical variation in aggregation pheromone response of I. subelongatus in northeastern China. Future research on the pheromone production and response of I. subelongatus from different regions in Northeast Asia will surely improve our understanding of the dynamic aggregation pheromone system of this economically important forest pest insect.