Feeding on mature potato foliage and low temperatures can influence diapause preparation and winter survival in insects adapted to northern regions such as the Colorado potato beetle (Leptinotarsa decemlineata Say). The effects of potato leaf maturity and temperature regimen, in a full factorial combination, on prediapause feeding, digging depth in the soil, and survival after a brief exposure to −2°C were studied in beetles induced to diapause under short day conditions in the laboratory. Newly emerged adults were fed either younger or older potato leaves (cultivar Norland) at temperatures cycling daily according to a sine wave averaging 17 or 11.5°C. As expected, time spent feeding before satiation was significantly longer at 11.5°C (25 ± 1.12 [SE] d) than at 17°C (17 ± 0.37 d); leaf age or its interaction with temperature had no significant effect. Beetles consumed older foliage at a faster rate, especially at the 17°C regime. Cumulative fresh weight of older leaves consumed before satiation was 45% higher (3.50 ± 0.07 g/beetle) than young leaves (2.25 ± 0.05 g/beetle); temperature regime and the interaction were nonsignificant. Despite variation in feeding rate and feeding time before satiation, weight gain during prediapause (25–30 mg/individual) remained nearly constant over all factor combinations. Thus, metabolic reserves for overwintering in terms of weight gain are more or less fixed, and any variations in food quality and temperature are compensated for by varying feeding behavior. Satiated prediapause beetles showed no significant variation of postfeeding delay before initiating digging; this delay averaged 8 d under all conditions. Mean depth reached in soil columns before final resting was 30 ± 2.1 cm at 11.5°C compared with 45 ± 2.4 cm at 17°C, with no significant effect of leaf age or interaction. Thus, feeding on older foliage did not affect overwintering depth. Survival after a 4-h cold shock at −2°C, after 6 mo at 4°C, was 59% for beetles under the 17°C regime during prediapause compared with 84% for those under the 11.5°C regime during prediapause. Our results show that a higher temperature regime during prediapause preparation reduces beetle resistance to frost in late dormancy, but beetles dig deeper at high temperatures, which could compensate for the higher risk of freezing.
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