Critical lethal temperature of a water strider, Aquarius paludum is about – 3 ºC that is much higher than supercooling points (-7- - 17ºC on average): this means this species is “cold injury lethal type”. Short days induce longer survival hours for Nangoku (33ºN) strain rather than long-days, while the photoperiodic response for Sapporo (43ºN) strain is opposite to that for Nangoku strain: long-days longer survival hours. Population individuals of Nangoku strain appear on water bodies even in mid winter, and the high cold-hardiness helps them to survive occasional sever low temperature on water bodies in winter. Overwintering adults of Sapporo strain are gardened by snow fall from sever condition in winter, while occasional low temperature in spring or late autumn may be dangerous for the reproductive adults in those seasons. For A. paludum and the relative species of water striders, Gerris nepalensis and G. latiabdominis in Kochi (33ºN), overwintering and diapause adults on land showed higher desiccation resistance than reproductive and overwintered adults collected from water bodies in spring. Adults of G. latiabdominis which uses exclusively temporary water bodies were more resistant to drought both in overwintered reproductive and overwintering diapause generations rather than G. nepalensis using exclusively permanent waterbodies. Higher resistance to drought shown by embryos of A. paludum and G. latiabdominis rather than that for G. nepalensis seems to be related to their habitats including temporary bodies easy to be drought up. For water striders in Gerrinae inhabiting mainly standing fresh waters, habitat stability of water bodies can be more directly reflected to the hardiness to desiccation rather than all the other exclusively terrestrial insects.
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