LIFE-HISTORY OF AMPHINEMURA DECEMCETA OKAMOTO (PLECOPTERA)

This paper deals with the life history of Amphinemura decemceta Okamoto, based on field and laboratory observations at Iiyamashi, Nagano Pref., in central Japan. 1. Egg : ellipsoidal, colourless, and covered with gelatinous material. The egg measured on the chorion is 150-170μ along the long axis and 120-130μ along the short axis in length. The egg preserved in alcohol weighs 0.0015mg on the average. 2. First instar larva : the antennae are composed of 9 joints and the cerci of 4 joints. The larva has no prosternal gills on the ventral side of the prothorax. The body is 486-639μ, the antennae 297-333μ, and the cerci 180-216μ in length. 3. Imago : the body is 5.5-7.5mm long in the female and 5.5-6.5mm in the male. The fore-wing measures 8.0-8.5mm in the female and 6.5-7.0mm in the male from the base to the tip. The specimens preserved in alcohol weigh 4.0mg in the female and 2.2mg in the male, on the average. 4. Hatching is observed from the end of December to the end of January. The duration of the egg stage takes 34-82 days in the water temperature range 6.3-12.3℃. The percentage of hatching varies from 90 to 100%. 5. In one instance the larval stage takes 286 days, during which it passes 14 instars ; each instar takes 14-32 days in the water temperature range 7.5-17.3℃. In individuals that grow quickly, however, the larval stage takes 134-145 days. 6. The body length increases eight times during the whole larval life. The rate of increase is larger in the seventh and eighth instars than in the other. 7. The larva is herbivorous, feeing on fallen leaves and benthic algae. 8. The emergence takes place in spring and autumn. Adult flies have partly emerged in May while mostly from beginning of October to middle of December. The start of emergence in the autumn has been observed at the average air temperature of about 18℃, and the greatest frequency of emergence at 10-16℃. 9. The sex-ratio was ♀100 : ♂75.5 in 258 individuals. 10. The adu lt is herbivorous, feeding on fallen leaves. It feeds, however, in a small quantity. 11. The position assumed during copulation is similar to that in other stoneflies. The season of oviposition is found in November in the adults which emerge in autumn. The number of eggs deposited by one female varies from 200 to 326. 12. The imaginal duration takes 2-22 days in the female and 2-14 days in the male.