Latitudinal variation in Dendroctonus ponderosae (Coleoptera: Scolytidae) development time and adult size

Dendroctonus ponderosae (Hopkins) is widely distributed across western North America, feeding in at least 12 native species of Pinus L. (Pinaceae). We investigated the existence of heritable differences in two life-history parameters (adult size and development time) of D. ponderosae from a northern population (central Idaho, Pinus contorta Douglas ex Loudon) and a southern population (southern Utah, Pinus ponder osa Douglas ex P. and C. Lawson). We attempted to separate heritable from environmental effects by rearing individuals from both populations through two generations (F-1 and F-2) in a common standardized laboratory environment with a constant temperature. Two treatment effects were tested for in the F-2 generation: (I) geographic location (source host) for F-0 D. porderosae; and (2) the F-2 brood host. We hypothesized that, if differences were observed and the F-0 source host and region had a greater effect on F-2 brood development time and adult size than did the host in which F-2 brood were reared, a heritable factor related to the F-0 parents was responsible. Time to emergence was significantly shorter for second-generation offspring of the northern population than for second-generation offspring of the southern population, regardless of the F-2 brood host. Although both the F-2 brood host and F-0 source parents were significant in explaining differences observed in the developmental-time distribution of F-2 brood, the F-0 source effect was round to be much greater. Also, F-2 males and females from southern source parents were sig nificantly larger than F-2 brood from northern source parents when reared in both F-2 brood hosts. Geographic region and original host of F-0 source parents had a significant effect on F-2 offspring size, whereas the immediate food for F-2 brood was not significant in explaining differences. These results suggest genetically based regional differences in D. ponderosae populations.