Effects of Temperature and Photoperiod on Reproduction in the Giant Water Bug, Lethocerus deyrollei (VUILLEFROY) (Heteroptera : Blastomatidae)

The environmental factors controlling reproduction in the giant water bug, Lethocerus deyrollei (VUILLEFROY) are examined under natural and laboratory conditions. Transfer of adults from natural conditions to a high temperature (28℃) in spring induced earlier onset of oviposition under either the natural or a long-day (LD 16 : 8) photoperiod. Female adults that had begun to lay eggs in summer continued oviposition in autumn when transferred to a long-day photoperiod (LD 15 : 9), whereas they stopped it under the natural photoperiod irrespective of whether the temperature was 28℃ or natural. Female adults that emerged in summer entered diapause and maintained it under the natural photoperiod at either 28℃ or the natural temperature, whereas their ovaries developed when transferred to the long-day conditions. Thus, water temperature is the key factor in determining the onset of reproduction in summer, and photoperiod plays the major role in the induction and maintenance of diapause after reproduction.