スジコガネの草地と林地間の飛翔と体内状況  [in Japanese] On the Flight of Mimela testaceipes between Sward and Forest, in Relation to its Internal Conditions (Coleoptera, Scarabaeidae)  [in Japanese]

コガネムシの羽化成虫が多い草地で, 成虫の飛翔虫数と飛翔方向について, 1979年7月下旬∿8月下旬にほぼ毎日調査した.これと同時に捕獲した飛翔虫の種構成から, スジコガネの方向別飛翔虫数を推定した.また, 飛翔虫と林地などで得た成虫について, 性比・交尾率・卵巣成熟程度・蔵卵数を調査し, その推移からスジコガネ成虫の行動経過を推定した.1.飛翔虫数は, 日没後30∿50分の約20分間に多く, 主な飛翔方向は幼虫が生育した草地と成虫が集合する林地の2方向に固定されていた.日別の飛翔虫数は変動が大きく, その季節的推移には一定の傾向が見いだせなかった.2.飛翔方向は, 飛翔初期は林地方向のみ, 中期以降には草地方向が加わった.飛翔後期の8月下旬には林地方向がなくなり, 草地方向も中期とは別の方向となった.3.林地方向へ飛翔する群の構成は, 1)初期に多い羽化脱出直後の未成熟雌, 無効雌および雄, 2)中期以降に多い既交尾の無蔵卵雌・少数蔵卵雌, 3)中期以降過半数を占める既交尾の多数蔵卵雌, の3つより成っていた.4.草地方向へ飛翔する群は, 大部分が25∿60個と多数蔵卵した既交尾の成熟雌で, これらは草地へ産卵のために飛翔してくると考えられた.5.林縁の針葉樹には成虫の集団が見られ, ここで摂食・交尾・卵巣成熟がなされる.6.以上の経過について整理し, その機構についてヨーロッパコフキコガネと対比して考察した.また, スジコガネ幼虫の被害集中の理由について考察し, それが成虫の集団飛来に起因する可能性があることを指摘した.

A field observation was carried out on flying adults of Mimela testaceipes MOTSCHULSKY, a serious pest on grass and conifers, at a heavily injured sward near coniferous forest in northern Hokkaido, Japan, through the whole flight season, from late July to late August, 1979. The flight activity in a day was concentrated at dusk from 30 to 50 minute after sunset, and the daily abundance of flying chafer was very variable during the season. Independently of wind directions two main tracks of flight were recognized. One is a track toward the forest observed in the early to middle flight season, and the other an opposite one, namely toward sward in the middle to late season. Males were found among the population flying toward forest in early flight season, and not found in the population toward sward. The females flying toward forest are composed of 1) newly-emerged females, including some barren ones, mostly found in the early flight season, 2) postoviposition females, containing no or only a few eggs, mostly found in the middle season, and 3) mature females, containing many fully-formed eggs, mostly found in the middle and late season. It is difficult to understand the reason why a lot of mature females leave sward, the oviposition site of the species, and fly to forest. The females flying toward sward are composed of only mature ones, mostly mated and containing 25-60 fully-formed eggs. The coniferous forest, on which aggregation of chafers was observed, may be important as a site of feeding, mating and egg-developing especially for newly-emerged chafers. A process of the adult behavior of Mimela testaceipes was presumed and was compared with that of Melolontha melolontha L. in Switzerland given by SCHNEIDER (1952). As a conclusion it is pointed out that the mass flight of mature females toward sward may be one of the main causes of the concentric occurence of larvae in sward.