Role of Some Additives for Enhancing Entomopathogenic Biocontrol Agents against Larvae of the Cotton Leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

Ascorbic acid, citric acid, glucose, L-alanine, potassium chloride and sodium carbonate were added to improve the potency of some entomopathogens; Bacillus thuringiensis (Bt) subsp. kurstaki; Metarhizium anisopltae (Metsch.); Heterorhabditis bacteriophora (Poinar) and Steinernema abbasi (Elawad) against 4th instar larvae of the cotton leaf worm Spodoptera littoralis (Boisd.). Bt had the most efficacy compared to the other entomopathogens after 2 days from treatment. M anisopltae was the most potent after 4 and 7 days post treatments. Additives from ascorbic acid, potassium chloride and sodium carbonate at a concentration of 0.025% enhanced Bt effect and caused potential interaction on S. littoralis larval mortality percentages. Other additive compounds caused additive interaction for Bt., except for citric acid (0.1%) and glucose (0.1%) that caused antagonistic effect for Bt and reduced larval mortality. On the other hand, potassium chloride and sodium carbonate at concentration of 0.025% potentiate M anisopltae efficacy against tested larvae. Ascorbic acid (0.05 and 0.025%), citric acid (0.1, 0.05 and 0.025%), glucose (0.05%), potassium chloride (0.1%) and sodium carbonate (0.05%) caused additive interaction with M anisopltae. Meanwhile, the other tested additives decreased M anisopltae efficacy and caused antagonistic effect on larval mortality. H. bacteriophora had additive effect when all the tested additive compounds were added to it, except glucose (0.1%) that caused antagonistic interaction with H. bacteriophora and decreased the mortality of larvae. All additive compounds caused additive interaction with S. abbasi against S. littoralis larvae, except for ascorbic acid (0.025%), glucose (0.1%) and sodium carbonate (0.025%) that had antagonistic interaction with S. abbasi.