OPTIMAL ATTACK DENSITY IN THE LARCH BARK BEETLE, IPS-CEMBRAE (COLEOPTERA, SCOLYTIDAE)

1. The effects of attack density of the larch bark beetle, Ips cembrae (Heer) (=Ips subelongatus Motsch.) on the gallery length, egg and offspring adult production and mortality were studied in 0.1 m2 bark samples from 100 larch trees (Larix dahurica Turcz) during the summer of 1989 in a burned area of the Tu Qiang Forest District, Great Xingan Mountains, P.R. China. 2. The results show that there is a positive linear relationship between gallery length and number of egg niches. The number of egg niches and off-spring adults produced per gallery declined exponentially with attack density, and the egg to adult mortality increased exponentially as the attack density increased in the absence of host resistance. 3. The exponential relationships are attributed to intraspecific competition between female parent adults for breeding space and between larvae for limited food resources. 4. In addition, there are two optimal attack densities, 13.9 attacks per 0.1 m2 and 8.7 attacks per 0.1 m2, at which the number of egg niches (935) and offspring adults (496) are maximal, respectively. An upper threshold of attack density, 31.8 attacks per 0.1 m2, beyond which the number of offspring adults produced from a bark area become less than the input of parent adults was also found.