小木原湿地（山口県萩市）におけるエゾスズ Pteronemobius yezoensis Shiraki（ Orthoptera: Trigonidiinae）の生活史（1）生態・卵期間・卵サイズ

Life cycle of Pteronemobius yezoensis Shiraki (Orthoptera: Trigonidiinae) in Kogihara wetland, Hagi City, Yamaguchi Prifecture (1) Ecology, egg period, and egg size

Creators ARAI Tetsuo

Creators Ikuta (Hosoda) Madoka

The ground cricket, Pteronemobius yezoensis Shiraki (Orthoptera: Trigonidiidae), distributed from Hokkaido to Kyushu and has an annual life history. The eggs of cricket have no diapause and they overwinter as nymphs. The life history of the crickets in the Kogihara wetlands in Hagi City (formally Asahi-son, Abu District), Yamaguchi prefecture (34.2º north latitude, 131.5º east longitude, approximately 400 m above sea level) was considered from the population dynamics in the field, egg incubation time, and egg size. Between April 1st to 24, 2004, there were a small number of third nymphal instars before emergence and a large number of first to second nymphal instars before emergence that overwintered. From April 28, most of the nymphs were first to second nymphal instars before emergence. Adults began to appear on May 19, and almost all nymphs were adults by late June. From late July to the beginning of August, first to second nympal instars were observed, and by the beginning of October, many were third nymph instars before emergence. Later, the development of nymphs stopped or was delayed, and the insects overwintered as nymphs. During the winter, the ground surface can freeze, and nymphs are almost never seen on the ground surface except during the daytime when the temperature is high. The crickets start to become more active with the rise in temperature from mid-April, and adults appear from mid to late May. The mean egg incubation period was 13.9, 12.5, 17.6, 34.4, and 88.7 days at 35 ºC, 30 ºC, 25 ºC, 20 ºC, 15 ºC, respectively. The variation in hatching was extremely small at any temperature but was slighter large at 15 ºC. The egg developmental zero was approximately 13 ºC. The hatching rate was ＞75% at 30 ºC, 25 ºC, and 20 ºC, but was 39% at 35 ºC and 49% at 15 ºC. Thus, 35 ºC is considered to be higher than the optimal temperature and 15 ºC is considered lower than the optimal temperature for the cricket eggs. The egg size immediately after laying was 1.6±0.05 mm on the long axis and 0.4±0,01 mm on the short axis. The eggs were immediately watered, and both the long and short axes started to increase in size. There was rapid growth between day 2 and 6 at 30 ºC, day 4 and 12 at 25 ºC, day8 and 20 at 20 ºC, and day 19 and 51 at 15 ºC

[ISSN]2189-4825