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

Abstract

AbstractDendroctonus 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 ponderosa Douglas ex P. and C. Lawson). We attempted to separate heritable from environmental effects by rearing individuals from both populations through two generations (F1 and F2) in a common standardized laboratory environment with a constant temperature. Two treatment effects were tested for in the F2 generation: (1) geographic location (source host) for F0D. ponderosae; and (2) the F2 brood host. We hypothesized that, if differences were observed and the F0 source host and region had a greater effect on F2 brood development time and adult size than did the host in which F2 brood were reared, a heritable factor related to the F0 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 F2 brood host. Although both the F2 brood host and F0 source parents were significant in explaining differences observed in the developmental-time distribution of F2 brood, the F0 source effect was found to be much greater. Also, F2 males and females from southern source parents were significantly larger than F2 brood from northern source parents when reared in both F2 brood hosts. Geographic region and original host of F0 source parents had a significant effect on F2 offspring size, whereas the immediate food for F2 brood was not significant in explaining differences. These results suggest genetically based regional differences in D. ponderosae populations.