Evaluation of mixtures of non-toxic vegetable oils and deltamethrin against susceptible and resistant strains of Tirbolium castaneum Herbst

The variation in the efficacy of deltamethrin formulated alone and in combination with five non-toxic vegetable oils, viz, sesame oil, karanj oil, neem oil, citronella oil and piperonyl butoxide in four ratios (1:1, 1:2, 1:4, 1%) was evaluated against the adults of susceptible (S) and resistant (R) strains of Tribolium castaneum Herbst by direct spray and film residue methods. All the vegetable oils proved additive when combined with deltamethrin except neem oil which showed antagonistic effect against the S-strain of T. castaneum. However, karanj oil and piperonyl butoxide synergised deltamethrin, while the remaining three vegetable oils exhibited additive action against the R-strain of T. castaneum when applied by direct spray method. With the change in the technique, ie., by film residue method, additive action was evidenced in the case of sesame oil, karanj oil, neem oil and piperonyl butoxide in mixed formulation with deltamethrin, whereas antagonistic action was exhibited by citronella oil against the S-strain of T. castaneum. In contrast, all the vegetable oils showed synergistic effect except neem oil which exhibited additive effect,against the R-strain of T.castaneum Irrespective of the method of application, karanj oil and piperonyl butoxide exhibited synergism with deltamethrin against R-strain of T. castaneum though additive action was obtained against the Sstrain. Further, 1:1 ratio of insecticides: non-toxic vegetable oil exhibited synergistic effect in R-strain, whereas no such effect was observed in S-strain.