HOST SELECTION BY THE FIR ENGRAVER, SCOLYTUS VENTRALIS (COLEOPTERA: SCOLYTIDAE): PRELIMINARY FIELD STUDIES

Publisher Website
Google Scholar
Abstract
Daily emergence of Scolytus ventralis Lec. from infested white fir bolts was highest in early afternoon (1200–1600 hours, P.D.S.T.) and limited to periods when air temperature exceeded 21 °C. More females than males emerged each day; the ratio in the total emergence was 1.9:1 and as high as 2.8:1 on warmest days. Flight occurred from mid-July to mid-September, with peak flight in mid-August. The intensity of flight activity was positively associated with varying temperatures above 24 °C (threshold).Visitation rates on lower boles of white firs were 10 times higher than those on Jeffrey pines. Two to three times as many beetles were trapped near girdled or severed white firs as about uninjured firs. Severed trees under attack by S. ventralis attracted three to seven times as many beetles as uninjured firs. When attack density reached 10 to 13 mines per sq. ft, the large number of beetles attracted in flight did not initiate mines in the trees already attacked but attacked surrounding host trees. Sex ratios of beetles trapped at experimental and control trees did not differ from that at emergence.
Keywords