Oogenesis in endemic Scolytus multistriatus (Marsham) (Coleoptera: Scolytidae) populations and the implications for host selection behavior

Twig-feeding by Scolytus multistriatus is a pre-vitellogenic feeding. Artificial diet studies were used to demonstrate that S. multistriatus females required a pre-vitellogenic feeding on a diet containing protein in order to complete oogenesis. Female S. multistriatus that did not ingest protein failed to complete oogenesis.;The timing of oogenesis during dispersal was determined using live-traps baited with the S. multistriatus aggregation pheromone. Female S. multistriatus responding to the aggregation pheromone in Seattle and Portland exhibited fully developed oocytes and evidence of twig-feeding. Furthermore, a large portion of the females had been mated prior to responding to the aggregation pheromone.;There are two periods in the S. multistriatus life cycle during which the female can engage in pre-vitellogenic feeding; twig-feeding during dispersal and feeding in phloem during egg gallery excavation. The Seattle and Portland populations appeared to use twigs exclusively for pre-vitellogenic feeding. This observation differed from reports on other field populations of S. multistriatus. The hypothesized explanation for the differences was that the Seattle and Portland populations were at endemic levels, while other populations were studied at outbreak levels.;Endemic conditions likely favor individuals that are physiologically and genotypically predisposed to long distance dispersal flights and twig-feeding behavior. Conversely, outbreak conditions likely favor individuals that are responding immediately to pheromone cues and forgoing long distance dispersal. As the dispersal environment shifts between endemic and outbreak conditions, the numbers of individual beetles exhibiting the dispersal behavior favored by the current conditions should increase. This would explain the differing observations between the Seattle/Portland population and other elm bark beetle populations.