PRIMARY ATTRACTION OF THE FIR ENGRAVER, SCOLYTUS-VENTRALIS

In laboratory bioassays, Porapak Q-captured and steam-distilled volati les from the bark of host trees, Abies grandis, particularly from root -rot-infected trees, attracted 50-70 % of male and female fir engraver s, Scolytus ventralis. Gas chromatographic-electroantennographic detec tion (GC-EAD) analyses of Porapak Q-captured bark volatiles revealed 1 9 EAD-active compounds of which 13 (mostly monoterpenes) were identifi ed by GC-mass spectrometry (GC-MS). In separate field experiments, mul tiple-funnel traps baited with two blends of these 13 synthetic volati les released at 280 and 340 mg/24 hr attracted 66 and 93% of the total S. ventralis captured, respectively. The clerid predator, Thanasimus undulatus, also responded strongly to the kairomonal volatiles. Additi onal experiments produced no evidence for aggregation pheromones in S. ventralis. These included laboratory bioassays and GC and GC-EAD anal yses of Porapak Q-captured volatiles from male- and female-infested lo gs or trees undergoing mass attack in the field, GC analyses and/or bi oassays of extracts from female accessory glands, extracted volatiles from emerged, attacking and juvenile hormone-treated beetles of both s exes, and videotape analysis of the behavior of attacking beetles on t he bark surface. We argue against the hypothesis of pheromone-mediated secondary attraction in S. ventralis and conclude that the attack dyn amics of this species can be explained solely by its sensitive primary attraction response to host volatiles.