Effects of Population Density on the Duration of Nymphal Period and Diapause-posture at the Adult Stage in a Water Strider, Gerris latiabdominis (Hemiptera : Gerridae)

The nymphal period of the water strider Gerris latiabdominis MIYAMOTO (Heteroptera : Gerridae) reared under high density (6.3-6.0 nymphs/100cm^2) was significantly shorter than that of those reared under low density (1.6-1.3 nymphs/100cm^2). High or medium density (3.1-2.3 nymphs/100cm^2) during the nymphal stage resulted in a higher percentage of adults showing diapause-posture than that in the low density group from the 11th to the 30th day after adult emergence. The high temperature of 31℃ induced reproductive diapause regardless of densities in nymphal stage even under long-day lengths. Nymphs of G. latiabdominis may respond to high density going with reduction in water surfaces before or after the rainy season which is the second half of June and the first half of July in Japan.