Emergence and Mating in Scolytus multistriatus (Coleoptera: Scolytidae)1

Abstract

Emergence of adult Scolytus multistriatus Marsham from naturally infested elm logs held under 3 environmental regimes was monitored during 1971 and 1972. The major emergence occurred within an 8- or 9-dayperiod in June and peaked between the 4th and 6th days after initial emergence. The overall sex ratio of emerging adults was 1:1 and there was no significant difference in the diel pattern of emergence of the sexes. In 1972 females predominated during the earlier part of the emergence period while males predominated in the later, but this pattern was not observed in 1971. Adults emerged at all times of day under constant conditions (26.7°C, 74% RH) but exhibited strong diel patterns peaking between 11 AM and noon during 1971 and from 8-9 AM during 1972. Emergence of beetles reared under ambient conditions and in an environmental chamber (12 h at 31.1°C; 12 h at 16.7°C) in 1971 also peaked strongly between 11 AM and noon. Adults did not emerge at or below 20 °C. Males demonstrated a propensity for multiple matings. When caged with an elm bolt and 100 females, a single male fertilized an average of 17 females. Increasing the number of males per 100 females resulted in higher numbers of fertile galleries, but even when the sex ratio was 1:1 some galleries were sterile. Insemination occurred on elm twigs and on an artificial substrate. Field-trapping inseminated females confirmed that mating commonly occurs prior to their arrival at the breeding site.