PARENT SESSION
Poster Session #28: Animal Ecology.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Condition-dependent habitat selection in Douglas-fir beetles.

Reid, Mary¹, ¹

ABSTRACT- When individuals are searching for habitat, those individuals with poorer dispersal ability may accept habitat of lower quality than would more capable dispersers. In this study, I examined the quality of habitat-seeking Douglas-fir beetles (DFB), Dendroctonus pseudotsugae, in relation to the density of conspecifics already at the breeding sites. Douglas-fir beetles are attracted to the pheromones of breeding conspecifics. Seasonal variation in the quality of available settlers was determined using standard funnel traps baited with synthesized DFB pheromones. This revealed that beetle weight remained constant, body size increased, and % fat decreased over the season. Beetles visiting breeding sites on both felled and live were sampled with clear barrier traps affixed to the trees. As breeding density increased in both felled and live, visiting beetles weighed less, were smaller, and tended to have less fat. These results are opposite to the seasonal pattern for weight and size, suggesting that beetles with lower dispersal ability are more willing to accept higher breeding densities than are larger and heavier beetles. More generally, these results indicate that attraction to conspecific pheromones in DFB may be due to the costs of searching for habitat rather than post-settlement benefits.

KEY WORDS: bark beetle, scolytidae, conspecific attraction, body size