Date of this Version
The pattern of geographical differences in two populations of the Colorado potato beetle, Leptinotarsa decemlineata (Say), suggests that preimaginal developmental responses and imaginal reproductive responses to temperature are under different selective pressures. Immatures from the warm, coastal (Long Island) area developed slightly slower, had slightly higher thermal thresholds for development, and suffered more mortality at low temperature than immatures from cooler, Upstate New York. However, more females from the Long Island population oviposited fertile eggs at lower temperatures than females from the upstate population. The data suggest that early planting dates and/or bivoltinism in the warm coastal area cause significant selection pressure for fast reproductive development under low temperatures. However, these factors do not seem to cause similar selection in the Long Island population for fast preimaginal development under low temperature. Immatures from a single egg mass show considerable variation in developmental rates in the field, especially on Long Island. Such large variation was not evident under constant temperatures, nor did laboratory-derived thermal responses to temperature provide accurate predictions of development in the field at either the coastal or the inland site. Thus, models for predicting development in the Colorado potato beetle should be modified to include environmental factors in addition to temperature; genetically and environmentally mediated variation in development should also be explored.