Residual toxicity of some synthetic pyrethroids against gram pod borer, Heliothis armigera (Hübner) infesting pigeonpea

The residual toxicity of eypermethrin (0.006%), fenvalerate (0.008%), deltamethrin (0.002%) and endosulfan (0.07%) on pigeonpea 1,3,7,10 and 15 days after spraying were evaluated against 7 to 8-day old larvae of Heliothis armigera (Hubner). The PT values for cypermethrin, fenvalerate, deltamethrin and endosulfan were 734.19, 695.01, 546.66 and 639.18 during the first season; and 775.20, 720.63, 494.47 and 696.27 in the second season. The averages of two seasons for these insecticides were 761.64, 708.51, 577.71 and 683.52, respectively. While taking endosulfan as unity, the RPT values for cypermethrin, fenvalerate and deltamethrin were 1.15, 1.09 and 0.86 during the first season; and 1.11, 1.03 and 0.71 in the second season. The averages of two seasons were 1.11, 1.04 and 0.85. respectively. Evidently, cypermethrin was the most persistent and effective insecticide followed by fenvalerate, endosulfan and deltamethrin.