Simulated winter to summer transition in diapausing adults of the lady beetle ( Hippodamia convergens ): supercooling point is not indicative of cold‐hardiness
1989; Wiley; Volume: 14; Issue: 4 Linguagem: Inglês
10.1111/j.1365-3032.1989.tb01103.x
ISSN1365-3032
AutoresLLOYD E. BENNETT, Richard Lee,
Tópico(s)Neurobiology and Insect Physiology Research
ResumoABSTRACT. 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 4d̀C for 6 weeks. In order to simulate the winter to summer transition, the beetles were transferred to 20d̀C and 68% r.h. under a LD 12:12h cycle. Supercooling points increased slightly from ‐ 16d̀C 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 ‐ 5d̀C, 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 20d̀C, 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 20d̀C 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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