Importance of Log Size on Host Selection and Reproductive Success of <I>Ips pini</I> (Coleoptera: Scolytidae) in Ponderosa Pine Slash of Northern Arizona and Western Montana

Abstract

Pine engraver, Ips pini (Say), often use thinning slash, and their populations are known to be influenced by the condition of this material. In our study, we evaluated the importance of three log diameters (5, 10, and 20 cm) and three lengths (60,120, and 240 cm) on various parameters of bark beetle host attack, development, and emergence. Evaluation of slash colonization in northern Arizona (near Flagstaff) and western Montana (near Missoula) over several years, during both spring and summer reproductive periods, indicated that the size of material selected by pine engraver differed by state, year, and season. However, within individual trials and over all trials, a trend in preference for larger diameter logs was apparent, whereas log length was of little effect. When evaluating only attacked logs, results indicated that the apparent preference for larger logs was not followed by significantly greater reproductive performance in the larger log sizes. Log origin was tested as a potential factor for the difference in attack densities between Arizona and Montana trials. Although male beetles in Montana and female beetles in Arizona seemed to distinguish between local-source and foreign-source logs during the attack phase, the gallery development and reproductive success of egg, larval, and new adult stages were not significantly different. Ultimately, differences among the trials both in host size selection and in reproductive success within attacked logs were closely tied to the overall population density of adult beetles. The implications of these findings for resource managers are discussed.