Cold Acclimation and Supercooling Capacity of Agasicles hygrophila Adults.

Simple Summary: The chrysomelid beetle Agasicles hygrophila is an effective natural enemy used in the biocontrol of the invasive weed Alternanthera philoxeroides. However, few studies have focused on the cold acclimation of A. hygrophila. We investigated the effects of exposure to different sub-lethal low temperatures for different durations on biological indices of adult male and female A. hygrophila and subsequently selected an appropriate acclimation temperature to enhance low-temperature tolerance. We found that A. hygrophila can acclimate to the cold and that this acclimation can enhance the cold tolerance of this beetle at −10 °C. Moreover, an appropriate acclimation temperature and time were found to enhance the survival and longevity of captive-bred A. hygrophila adults, which has ecological relevance for the biological control of A. philoxeroides in cold areas of northern China. Agasicles hygrophila Selman and Vogt is used in the biological control of the invasive weed Alternanthera philoxeroides (Mart.) Griseb. However, with the northward establishment of A. philoxeroides in China, the weak adaptivity of A. hygrophila to cold weather has resulted in the ineffective control of A. philoxeroides in northern China. Cold acclimation can significantly enhance insect cold tolerance, enabling them to cope with more frequent climate fluctuations. To improve the biological control efficacy of A. hygrophila in cold climates, we compared the effects of rapid cold hardening and acclimation on A. hygrophila under laboratory conditions. On initially transferring adults from 26 to −10 °C for 2 h, mortality reached 80%. However, when pre-exposed to 0 °C for 2 h and then transferred to −10 °C for 2 h, adult mortality was reduced to 36.67%. These findings indicate that cold acclimation can enhance the cold tolerance of A. hygrophila under laboratory conditions. However, the beneficial cold acclimation effects waned after more than 15 min of recovery at 26 °C. Exposure to 15 °C for 24 h or gradual cooling from 0 to −10 °C at 1 °C·min−1 also induced cold acclimation, indicating that long-term cold and fluctuating cold acclimation are also potentially effective strategies for enhancing low-temperature tolerance. [ABSTRACT FROM AUTHOR]