Effectiveness of Several Insecticides to Tobacco Cutworm, <i>Spodoptera litura</i>, on Soybean

Abstract

Effectiveness of several insecticides for the control of tobacco cutworm, Spodoptera litura (F.), was evaluated in field and laboratory tests. Liquid and dust formulations of these insecticides were applied to soybean cultured in fields alternating with rice paddys at the time of the scattering of the insect's newly hatched and full-grown larvae. In early stage application, most of the test insecticides were effective in the indexes of corrected density of survivals, while in later stage application, methomyl, acephate, EPN, and chlorpyrifos methyl were effective in the indexes and the observation of injurious leaves of the plant. LD50 of these insecticides against 3rd, 4th, and last instar larvae reared on an artificial diet were determined by a topical application method. The values for 3rd instar larvae were in the range of 0.16-4.6μg/insect, while those for last instar larvae were in the range of 2.8-66.8μg/ insect. Less than 5μg/insect of LD50 for last instar larvae, which seemed to be the level of direct deposition on larval body, were demonstrated by methomyl, chlorpyrifos methyl and profenofos. LC50 of test insecticides determined by the leaf dipping method were in the range of 12.7-121ppm for 3rd instar larvae and 44.3-711ppm for last instar larvae.