ヒメギス Eobiana engelhardti subtropica Bey-Bienko (Orthoptera: Tettigoniida) の卵休眠と生活史

Egg diapause and life cycle in Eobiana engelhardti subtropica Bey-Bienko (Orthoptera: Tettigoniida)

Creators ARAI Tetsuo

Eobiana engelhardti subtropica Bey-Bienko (Orhtopterra: Tettigoniidae) is distributed from Hokkaido to Kyushu and has an annual life history. The insects hatched between April to May and start to emerge around late June. They lay eggs from July to early October and overwinter as eggs. The eggs are one-year eggs and the diapause phase is at the prenymphal stage. When eggs were kept at 25 ºC after hatching, the egg weight immediately after egg-laying was approximately 3.3 mg, which increased linearly from 10 to 36 days after hatching to approximately 4.8 mg, reaching approximately 5 mg by day 48-52, with almost no change thereafter. The mean incubation time was 172.2 ± 12.6 days and 142.7 ± 19.1 days at 15 ºC and 20 ºC, respectively. When the eggs were maintained at 25 ºC or 30 ºC after egg-laying, the embryos developed to the pre-nymphal stage, but did not hatch and subsequently died. The effect of low temperature on breaking the diapause in eggs that reached the diapause phase was investigated. After being maintained at 25 ºC for 10 weeks, eggs were subjected to low-temperature treatments at 0-2 ºC, 7.5 ºC, 10 ºC, and 15 ºC for 3 to 24 weeks, after which the eggs transferred to 20 ºC with a 12L: 12D photoperiod. Irrespective of the lowtemperature treatment, the longer the duration of the low-temperature treatment, the shorter was the time to hating and the shorter was the mean incubation time after transfer. Concentration of hatching after low-temperature treatment was observed at ≧ 15, ≧ 12, and ≧ 15 weeks with treatment at low temperature of 0-2 ºC, 7.5 ºC, and 10 ºC, respectively. However, the concentration of hatching was lower at 15 ºC than that at the other low temperatures. The effect of low temperature on breaking the diapause in eggs before reaching the diapause phase was investigated. After being maintained at 25 ºC for 1 week or 3 weeks, eggs were subjected to low-temperature treatment at 7.5 ºC for 3 to 21 weeks, after which the eggs were transferred to 20 ºC with a 12L: 12D photoperiod. The eggs hatched even if low temperature (7.5 ºC) was encountered before the diapause phase, but the variation in hatching was large with the lowtemperature treatment for 3-18 weeks, and the hatching was concentrated at 21 weeks. In addition, the time until hatching was long, the variation in hatching was large, and the hatching rate was low compared with low-temperature treatment after the diapause phase.

[ISSN]2189-4825