Semiochemical Regulation of the Intraspecific and Interspecific Behavior of Tomicus yunnanensis and Tomicus minor during the Shoot-Feeding Phase

Two pine shoot beetles, Tomicus yunnanensis and Tomicus minor, are the most destructive pests of Pinus yunnanensis in southwestern China. We investigated behavioral responses within and between these two species during the shoot-feeding phase using walking bioassays. We also identified the pheromonal aspects of beetles by static solid phase microextraction (SPME) and hindgut extraction following interactive communication by gas chromatography-mass spectroscopy (GC-MS). Both species were significantly attracted by their own species and the same sex, and attraction was inhibited by exposure to additional beetles or to the hindgut extracts of beetles which had shown interaction. Female and male T. minor and T. yunnanensis hindguts contained 0.19, 0.09, 0.22, and 0.05 ng/individual of (-)-trans-verbenol, respectively; following interaction with additional beetles, this increased to 16.74-292.71 ng/individual in T. minor females. Mean concentration of verbenone detected in the hindguts of female/male individuals of T. minor and T. yunnanensis under natural conditions were 0.16, 0.06, 0.03, and 0.05 ng/individual, respectively, but these correspondingly increased to 5.90, 2.43, 0.06, and 0.19 ng/individual after exposure to additional insects. In T. yunnanensis, the amounts of detectable (-)-trans-verbenol and verbenone extracted from hindguts were lower than those from T. minor. The levels of cis-verbenol and (-)-trans-verbenol most attractive to walking T. yunnanensis and T. minor were 0.1 and 1.0 ng/mu l, respectively. Verbenone was not attractive at any of the concentrations tested. The addition of verbenone to cis-verbenol or (-)-trans-verbenol reduced the attraction responses. We conclude that the (-)-trans-verbenol produced by these two pine shoot beetles is attractive at low concentrations and repellant at high concentrations, thereby fostering intraspecific competition. Verbenone is produced to prevent overcrowding via interspecific inhibition, and to expel beetles during shoot-feeding.