Abstract
This study was conducted to investigate the seasonal occurrence of chestnut weevil, Curculio sikkimensis. The chestnuts infected by the weevils were collected from Gongju, Buyeo, and Cheongyang in Chungnam Province, Republic of Korea. Investigation was focus on the escape period of chestnut weevil larvae from the fruits, invading time and vertical distribution in soil, survival rates of larvae during overwintering, emergence period, emergence rate, and sex ratio and longevity of adults. For precocious species, larvae escaped the chestnut from the mid-September to the early-October, middle species and slow species, were escaped from the late-September to the mid-October and from the early-October to the mid-November. After escaping from the chestnut fruits all of the larvae burrowed into the soil within 35 minutes. Overwintering larvae inhabited in the range of $0{\sim}48cm$ from the soil surface and highly distributed in the range of $18{\sim}36cm$. The 74.1 % of wintering chamber were distributed within $18{\sim}36cm$ from the surface. Survival rates observed were 38.0% in 1st year, 16.0% in 2nd years, and 2% in 3rd years, respectively. Seasonal occurrence period of C. sikkimensis was from the early-Aug. to early-Oct. and the optimal occurrence period was the early and mid-Sept. Emergence rate decreased to 8.4% in 1st year, 3.6% in 2nd years, and 0.8% in 3rd years, respectively. Sex ratio was showed in the range of 0.51-0.55. It is female biased ratio. Longevity of adults was 9.9 days for female and 8.9 days for male.
2003년부터 2006년까지 충남 공주, 부여, 청양 지역에서 구입한 밤에서 탈출하는 밤바구미(Curculio sikkimensis) 유충의 탈출시기, 토양으로 잠입시간, 토중 분포상황 및 월동유충의 생존율과 성충의 우화시기 및 우화율, 성비 및 생존일수를 조사하였다. 밤바구미 유충의 탈출 시기는 조생종이 9월 중순부터 10월 초순, 중생종이 9월 하순부터 10월 중순, 만생종이 10월 초순부터 11월 중순에 탈출하였고, 탈출 후 35분 내에 100% 토양 속으로 잠입하였다. 밤바구미의 월동 유충은 지표면으로부터 48 cm 이내의 깊이에서 서식하였고, 18-36 cm의 깊이에서 74.1%의 분포를 보였다. 월동 유충의 생존율은 1년차에 38.0%, 2년차에 16.0%, 3년차에 2%로 조사되었다. 밤바구미 성충의 우화시기는 8월 초순부터 10월 초순까지로 우화최성기는 9월 초 중순이었다. 우화율은 1년차에 8.4%, 2년차에 3.6%, 3년차에 0.8%로 감소하였다. 성충의 성비는 $0.51{\sim}0.55$ 범위로 나타났고 암컷의 비율이 높았다. 생존일 수는 암컷이 평균 9.9일로 수컷의 8.9일보다 길어 암컷의 수명이 더 긴 것으로 나타났다.
