Termination of reproductive diapause in the rice water weevil with particular reference to the effects of temperature

Abstract

The period of diapause termination in adults (collected in Yueqing 120.94°E, 28.14°N, Zhejiang) of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), were determined by initially exposing diapausing adults to various constant temperatures (25–5°C) as well as to room temperatures (33–−1°C), and then transferring them at intervals to a climatically controlled chamber (26±1°C, using rice seedlings as adult hosts) where the dynamics of oviposition onset and the numbers of eggs deposited were observed. Under room temperature, the diapause in 1st- and 2nd-generation adults terminated around late September and early December, respectively, i.e. at ca. 2.5 and 2.0 months after collection. Diapause in both 1st- and 2nd-generation adults was significantly affected by temperature. When exposed to 10, 15 and 20°C, the diapause in most 1st-generation adults terminated after 75, 25 and 50 days, respectively, while in 2nd-generation adults it terminated after 50 days at each of these temperatures. The associated adaptive significance and geographical variation of diapause termination in this insect are discussed.