Evaluation of some non-toxic vegetable oils as synergists for different synthetic pyrethroids in mixed formulations against Tribolium castaneum (Herbst)

On the basis of joint action ratios, the type of action was categorized when three synthetic pyrethroids (deltamethrin, cypermethrin, fenvalerate) were used separately in mixed formulations with each of the four non-toxic vegetable oils (sesame oil, karanj oil, neem oil, citronella oil) and the well known standard synergist (piperonyl butoxide) in four ratios (1:1, 1:2, 1:4, 1:8), and evaluated against the susceptible strain of Tribolium castaneum (Herbst) adults by direct spray and film residue methods. Out of 30 combinations tested, additive action was obtained when these four different non-toxic vegetable oils were used in mixed formulations with cypermethrin and fenvalerate. With the exception of neem oil by direct spray method, the remaining three vegetable oils also showed additive action with deltamethrin. The antagonistic action, however, was produced by neem oil in the mixed formulation with deltamethrin. Only, the well known synergist PBO, synergised cypermethrin and fenvalerate. Obviously, the additive action obtained in 26 combinations suggested that the non-toxic vegetable oils maintained the desired toxicity of a particular insecticide tested, even though the reduction of toxicant was as high as nine times.