Simulated winter to summer transition in diapausing adults of the lady beetle (Hippodamia convergens): supercooling point is not indicative of cold-hardiness |
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Authors: | LLOYD E BENNETT RICHARD E LEE Jr |
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Institution: | Department of Zoology, Miami University, Hamilton, Ohio, U.S.A. |
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Abstract: | ABSTRACT. Adults of Hippodamia convergens Guerin-Meneville (Coleoptera: Coccinellidae) form massive overwintering aggregations in the Sierra Nevada Mountains of California. These diapausing pre-reproductive adults may remain in the aggregations for up to 10 months. Beetles were collected from overwintering sites in Nevada County, California, and held at 4 C for 6 weeks. In order to simulate the winter to summer transition, the beetles were transferred to 20 C and 68% r.h. under a LD 12:12h cycle. Supercooling points increased slightly from - 16 C on day 0 to - 12.9CC on day 21. In contrast, low temperature tolerance decreased markedly within 2 weeks. On day 0 nearly all beetles survive 2 h of exposure to - 5 C, whereas only 50% survived this treatment on day 4. These data demonstrate the general lack of correlation between the supercooling point and the lower lethal temperature in warm-acclimated beetles. Within 1 day of transfer to 20 C, oxygen consumption decreased by 26%. This decrease continued through day 14 when the rate of oxygen consumption had decreased to 40% of initial values. Beetles acclimated to 20 C selected temperatures significantly higher than cold-acclimated beetles. The parametric shifts observed in this study are consistent with a physiological transition from cold-hardiness and energy conservation during winter to one of dispersal, feeding and reproduction in summer beetles. |
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Keywords: | Diapause cold-hardiness acclimation Coccinellidae supercooling point |
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