摘要 : An experiment was conducted thrice in laboratory to test the activity of a biological insecticide, spinosad 45% SC (spintor) against the larvae of leaf skeletonizer, <i>Eutectona machaeralis</i> (Walker), a major pest of <i>Tecton... 展开 An experiment was conducted thrice in laboratory to test the activity of a biological insecticide, spinosad 45% SC (spintor) against the larvae of leaf skeletonizer, <i>Eutectona machaeralis</i> (Walker), a major pest of <i>Tectona grandis</i> L.f. (Family Verbenaceae). Results revealed that spinosad is highly toxic and induce larval mortality when applied on both host plant leaves and larvae together of the insect pest. Among the 11 concentrations of spinosad tested, cent per cent mortality was recorded by the higher concentrations of 10,000, 5,000, 2,500 and 1,250 ppm and significantly different (P<0.05) from other concentrations, except treatment 625 ppm concentration, which was recorded to be at par (P>0.05). There was significant difference (P<0.05-P<0.01) recorded among the treatments and control, but the dosage effect was not found to be conclusive (P>0.05). Further, there was a gradual decline of larval mortality in respect of lowering concentrations of the spinosad. The LC₅₀ value of the tested biological insecticide was worked out to be 61 ppm (0.000061%) against target insect pest. 收起