Economic Injury Levels for the Common Cutworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) on Soybean

The damage aspects of soybean by common cutworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) at different larval density and different growth stage of soybean were studied in soybean field. The percent yield reduction(Y) of soybean infested by different densities of S. litura (X, no. of larvae/plant) under outdoor conditions for a three week period were estimated by the following equations: (1) Y = 1.655X - 6.025 ($R^{2}=0.952$) for the R1 (flowering stage); (2) Y = 0.725X - 0.475 ($R^{2}=0.986$) for the R3 (beginning pod stage); and (3) Y = 0.635X - 1.325 ($R^{2}=0.986$) for the R5 (beginning seed stage). Based on the relationships between the densities of S. litura larvae and the yield index of soybean, the number of larvae (2nd-3rd instar) which caused 5% loss of yield (Tolerable injury level) was estimated to as approximately 6.7 for the R1, 7.5 for the R5, and 10.0 per plant for the R5, respectively. Average soybean leaf areas consumed by 1st, 2nd, 3rd, 4th, 5th and 6th larvae of Spodoptera litura during 24 hr at $28^{\circ}C$ was 0.3, 0.7, 2.6, 4.0, 20.1, and $55.8\;cm^{2}$, respectively.

콩 담배거세미나방(Spodoptera litura)의 경제적 피해수준

담배거세미나방에(Spodoptera litura)에 의한 콩의 피해해석을 하고자 콩 생육기 및 담배거세미나방 유충 밀도를 달리하여 조사한 결과 콩 생육시기별 유충 밀도에 따른 수량감소율과의 관계식은 개화기에는 (1) Y = 1.655X - 6.025 ($R^{2}=0.952$), 착협기에는 (2) Y = 0.725X - 0.475 ($R^{2}=0.986$), 립비대기에는 (3) Y = 0.635X - 1.325 ($R^{2}=0.986$)였다. 이 관계식을 근거로 하여 콩 생육시기별 피해허용수준(수량감소 5% 기준)을 산출한 결과, 주당 2-3령 유충의 밀도는 개화기6.7 마리, 착협기 7.5마리, 립비대기는 10.0마리였다. $28^{\circ}C$에서 1령, 2령, 3령, 4령, 5령 및 6령 유충의 1일 섭식량은 0.3, 0.7, 2.6, 4.0, 20.1 및 $55.8\;cm^{2}$ 이었다.