Natural History of Chlaenius cordicollis Kirby (Coleoptera: Carabidae) on Beaches of Lake Winnipeg, Manitoba, Canada

Observational and experimental natural history studies were carried out on Chlaenius cordicollis Kirby (Coleoptera: Carabidae) from beaches with limestone slabs (mostly 10–100 cm in diameter) on Hecla Island in Lake Winnipeg, Manitoba, Canada. Adult beetles moved down the beaches from overwintering sites in May, and in response to photoperiodic cues, females were gravid in June and July. Larval numbers peaked in early July and teneral adults in late August. At 21 °C, development from oviposition through three larval instars to adult eclosion took 44 days. Larvae were observed feeding on the remains of Ephemeroptera that had washed ashore and on Diptera larvae feeding on the remains. From mid-May until early September, guts of adult beetles contained insect fragments, primarily Chironomidae (Diptera) and Ephemeroptera. Outside this period, adult guts contained no solids and most were empty. In September, adults moved up beaches to overwintering sites, even though temperatures were similar to those during the down-beach movement of May. In fall, beetles aggregated in sites in gravel or shingle where leaf litter had accumulated; in these sites, snow accumulated in winter and temperatures in aggregations remained close to 0 °C—essential for survival of the adults. Survival of cold-adapted adults was jeopardized at temperatures of –5 °C or –9 °C, depending on the rate of cooling. Beetles became less agile at temperatures ≤ +5 °C; at ≤ +10 °C walking speed was negatively related to temperature. Hence, the normal up-slope movement in response to inundation could be impaired at temperatures experienced in September, a time when wind-driven, rapid increases in lake levels frequently occur.