배추에 대한 배추흰나비(Artogeia rapae L.)의 요방제수준

Control Thresholds (CTs) of Imported Cabbage Worm (Artogeia rapae L.) for Chinese Cabbage in Korea

배추에서 배추흰나비의 요방제수준을 설정하기 위해 온실 및 포장에서 실험을 수행하였다. 예비실험으로서 배추흰나비 2령충을 다섯 밀도 수준 접종하고 피해정도를 조사하였다. 배추 포기당 유충 1마리 접종에 의한 잎피해면적은 정식3주차 배추에서 섭식 1주일후 657.7 $mm^2$, 정식 6주차 배추에서 섭식 2주일후 2495.8 $mm^2$로 나타났다. 포장실험에서는 배추흰나비 유충 1-7마리를 시험구(배추 20주)에 접종하였다. 3주간 섭식후, 접종 유충 밀도(X)에 따른 수량감소율(Y)은 다음 두가지 식, 즉 정식 3주차 배추는 Y=1.7640X-0.3049 ($R^2$=0.9901), 정식 6주차 배추는 Y=1.0305X-0.2976 ($R^2$=0.9398)로 각각 추정되었다. 접종한 유충밀도와 배추 피해지수간의 상관성을 바탕으로, 수량 감소율(gain threshold, 수익역치) 5%로 전제한 배추흰나비 2령 유충의 요방제수준은 정식 3주차 배추에서 20주당 3.0마리, 정식 6주차 배추에서 20주당 5.1마리로 추정되었다.

This study was conducted to estimate the control thresholds (CTs) of imported cabbage worm, Artogeia rapae L., injuring Chinese cabbage. The second instar larvae of A. rapae were inoculated with five density levels on each Chinese cabbages transplanted three weeks earlier under greenhouse condition, and checked injury rates after allowing their feeding for one week and two weeks, respectively. The average leaf area consumed by single larvae was 657.7 $mm^2$ in plots inoculated at three weeks after transplanting (WAT) and 2495.8 $mm^2$ in plots at 6-WAT, respectively. In the field experiment, different numbers of A. rapae ranged from one to seven larvae were inoculated on 20 plants. The percent yield reduction (Y) of Chinese cabbage infested by different densities of A. rapae (X) for a three-week period was estimated by the following equation; (1) Y=1.764X-0.3049 ($R^2$=0.9901) in plots inoculated at 3-WAT; and (2) Y=1.0305X-0.2976 ($R^2$=0.9398) in plots inoculated at 6-WAT. Based on the relationships between the densities of A. rapae larvae and the yield index of Chinese cabbage, the number of second instar larvae which caused 5% loss of yield (gain threshold proposed by Japan), was estimated as 3.0 per 20 plants for the 3-WAT and 5.1 for the 6-WAT.