Temperature dependent winter survival of Bembidion lampros and Tachyporus hypnorum

Abstract

Wintering survival of the predatory beetles Bembidion lampros and Tachyporus hypnorum was tested under field conditions with manipulated periods of constant frost. Survival of both species was influenced negatively by short frost periods during an otherwise mild winter. Exposure to 2 weeks of frost during a mild winter reduced survival below 10%. Survival during a harsh winter with constant subzero temperature was high for both species. Overwintering survival was also tested experimentally under different temperature regimes in the laboratory. Survival of B. lampros at fluctuating temperatures between −2 °C and +6 °C, was lower when the temperature fluctuated on a weekly basis than on a daily basis. Survival of T. hypnorum was severely affected by fluctuating temperatures around 0 °Cindependent of the frequency. Winter survival was generally higher for B. lampros than T. hypnorum under equivalent temperature conditions both in the field and in the laboratory. Super cooling point (SCP) and weight changes were measured on individual specimens during overwintering under field conditions. SCP for B. lampros decreased as the winter became harsher while SCP for T. hypnorum seemed to be constant under the same conditions. At the end of the winter SCP for B. lampros increased dramatically. Weight changes of individual specimens were constantly low for both species during a harsh winter. Mean weight changes of B. lampros and T. hypnorum during overwintering was followed under different temperature regimes. Mean weight changes after the winter did generally not explain winter mortality.