Insecticidal activity of mixtures ofBacillus thuringiensiscrystals with plant oils ofSinapis albaandAzadirachta indica

Abstract

The main purpose of this study was to determine the insecticidal activity of mixtures ofBacillus thuringiensiscrystalline toxins and plant substances that could contribute to create a new bioinsecticide of high efficiency. We decided to determine the toxicity of crystals ofB. thuringiensisMPU B9 isolate, azadirachtin (NeemAzal), mustard oil and their mixtures against lepidopteran pests:Cydia pomonella,Spodoptera exiguaandDendrolimus pini. The interaction of the components in mixtures against insects was evaluated and their utility in plant protection was assessed. The crystals and plant substances showed synergistic effect against all insect species. The occurrence of synergism between two components depended on the ratio of their concentration in mixtures. Slight amount of one of the components added to the mixture led to enhanced toxicity of the preparation. The supplementation of mustard oil withB. thuringiensistoxins from up to 0.3% of the mixture resulted in more than twofold higher observed mortality of L1 larvae ofD. piniin comparison with expected mortality. The beneficial insecticidal effect of the mustard oil and crystals mixture was also noted when crystals comprised up to 1.3% and from 7 to 20% against L1 caterpillars ofC. pomonellaand L3 larvae ofS. exigua, respectively. The insecticidal efficient effect was achieved when mixture ofB. thuringiensiscrystals and azadirachtin was used against the three species of lepidopteran pests. The combinations in which components interacted synergistically against caterpillars are potentially useful for making a new bioinsecticide for controlling lepidopteran pests in plant protection.