Potency of Combinations of Bacillus thuringiensis and Chemical Insecticides on Spodoptera littoralis (Lepidoptera: Noctuidae)

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Abstract
We determined the effects of insecticides of different chemical groups on sporulation yields of Bacillus thuringiensis var.entomocidus. Among the carbamates tested, carbaryl had a more deleterious effect on the sporulation process of B. thuringiensis than methomyl. Within the organophosphorous group, phoxim inhibited sporulation less than profenofos. The pyrethroid group, represented by fenvalerate, cypermethrin, and permethrin, generally had less deleterious effects on sporulation of B. thuringiensis than did the carbamate and organophosphorous compounds. The pyrethroids and most organophosphorous compounds tested potentiated the activity of B. thuringiensis applied against the cotton leafworm, Spodoptera littoralis (Boisduval). The carbamates, diflubenzuron, and a combination of methomyl and diflubenzuron (disa) showed an additive effect when applied jointly with B. thuringiensis varieties. The mild effect of pyrethroids on sporulation processes of B. thuringiensis, compared to effects of other classes of chemical insecticides, suggested little or no interference with the ecology and perpetuation of this useful bacterium at the site of application. Synergistic interactions suggest that application of pyrethroids with B. thuringiensis may be a safe and effective means for controlling S. littoralis.

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