Vegetable oils as synergists of synthetic pyrethroids against diamondback moth, Plutella xylostella L. (Yponomeutidae: Lepidoptera).

Among the six oils screened, sesamum, honge and linseed oils greatly synergised fenvalerate. Honge oil alone at higher dosage (0.3 and 0.4%) showed significant insecticidal activity. Sesamum oil (0.2 per cent) recorded highest larval mortality of 81.50 and 99.99 per cent at 24 and 48 h, respectively and was significantly superior to other oils. Larval mortality with honge and sesamum oils in combination with synthetic pyrethroids increased with the increase in dosage and interval of observation. At the shortest interval of 24 h, honge oil and sesamum oil at 0.2 per cent synergised all the pyrethroids tested. Both sesamum and honge oils at 0.2 per cent can be utilized to prolong the efficacy of pyrethroids. Under field conditions these combinations showed varying degrees of synergism, which increased up to three days and declined there after indicating instability of these combinations.