COLD TOLERANCE IN THE COLORADO POTATO BEETLE, LEPTINOTARSA DECEMLINEATA (SAY) (COLEOPTERA: CHRYSOMELIDAE)

Abstract

AbstractThe seasonal change in the level of cold tolerance in a field population of Colorado potato beetle, Leptinotarsa decemlineata (Say), is described for a northern location. Survival of overwintering adult beetles is highest from September through January. After that it falls to a lower level that is maintained until beetle emergence in May or June. The seasonal change in the level of cold tolerance is parallel to the change in the intensity of diapause but not to the change in the low temperature exotherm. The value of the low temperature exotherm is variable but averages −8.8°C for active beetles on plants and −11.7°C for soil-collected overwintering beetles in their deep diapause phase. Experimental results suggest that reduction of the gut content and increase in the amount of body fat in diapausing beetles is sufficient to lower the low temperature exotherm by a few degrees. The diapausing state itself, without cold acclimation, is sufficient to increase cold tolerance. However, results suggest that it is not the level of cold tolerance of the Colorado potato beetle provided by the diapausing process that has allowed this species to extend its range northward into New Brunswick but its accompanying burrowing behaviour.