Division of Entomology, Indian Agricultural Research Institute, New Delhi-110 012 (India).
The non-toxic vegetable oils, viz., karanj oil, neem oil, citronella oil, and piperonyl butoxide (PBO) were separately used in the mixed formulations with cypermethrin in various ratios (1:1, 1:2, 1:5, 1:10) and evaluated against different instars, viz., 1, 4, 7 and 9-day old larvae of Spodoptera litura Fabricius by leaf dip and direct spray methods. The categorization of the type of action was based on joint action ratios for evaluating synergistic activity. With the change in age of S. litura larvae, the effect of method of application was evident on the synergistic activity of different vegetable oils. When leaf dip method was used, karanj oil synergised cypermethrin against 4,7 and 9-day old Iarvae. But with PBO, the synergistic activity was obtained only on advanced age, i.e., 7 and 9-day old larvae. In the case of direct spray method, the synergistic activity of neem oil in the formulation was pronounced against 4 and 9-day old larvae. Also, karanj oil exhibited synergism againt 1,7 and 9-day old larvae. But, citronella oil showed synergistic activity against only 7-day old larvae. The rest of the combinations showed additive action, irrespective of the method of application and age of the larvae, except against 1-day old larvae where antagonistic action was obtained with neem oil using leaf-dip method. Evidently with karanj oil, the type of action changed from additive to synergistic as the age of the larvae of S. litura increased from 1 to 9 days.
