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

Dendroctonus ponderosae (Hopkins) is widely distributed across western Nort h America, feeding in at least 12 native species of Pinus L. (Pinaceae). We investigated the existence of heritable differences in two life-history pa rameters (adult size and development time) of D. ponderosae from a northern population (central Idaho, Pinus contorta Douglas ex Loudon) and a souther n population (southern Utah, Pinus ponder osa Douglas ex P. and C. Lawson). We attempted to separate heritable from environmental effects by rearing i ndividuals from both populations through two generations (F-1 and F-2) in a common standardized laboratory environment with a constant temperature. Tw o treatment effects were tested for in the F-2 generation: (I) geographic l ocation (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 an d 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 relate d to the F-0 parents was responsible. Time to emergence was significantly s horter 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 d istribution of F-2 brood, the F-0 source effect was round to be much greate r. Also, F-2 males and females from southern source parents were sig nifica ntly 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 population s.