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

The seasonal change in the level of cold tolerance in a field populati on of Colorado potato beetle, Leptinotarsa decemlineata (Say), is desc ribed for a northern location. Survival of overwintering adult beetles is highest from September through January. After that it falls to a l ower level that is maintained until beetle emergence in May or June. T he seasonal change in the level of cold tolerance is parallel to the c hange in the intensity of diapause but not to the change in the low te mperature exotherm. The value of the low temperature exotherm is varia ble but averages -8.8 degrees C for active beetles on plants and -11.7 degrees C for soil-collected overwintering beetles in their deep diap ause phase. Experimental results suggest that reduction of the gut con tent and increase in the amount of body fat in diapausing beetles is s ufficient to lower the low temperature exotherm by a few degrees. The diapausing state itself, without cold acclimation, is sufficient to in crease cold tolerance. However, results suggest that it is not the lev el of cold tolerance of the Colorado potato beetle provided by the dia pausing process that has allowed this species to extend its range nort hward into New Brunswick but its accompanying burrowing behaviour.