Impact of simultaneous treatment of gamma irradiation and Bacillus thuringiensis on cotton leaf worm Spodoptera littoralis (Boisd.) (Noctuidae: Lepidoptera)

Abstract

Abstract Background The two biological control methods, inherited sterility technique (IST) and Bacillus thuringiensis (Bt), are considered as the two promising methods for lepidopteran pest management. Simultaneous treatment with both techniques was assessed against the cotton leaf worm, Spodoptera littoralis (Boisd.) (Noctuidae: Lepidoptera) compared to individual treatment for developing the lepidopteran management program. Results Pupation and adult emergence were significantly lower in simultaneous treatment than irradiated insects individually. Larval mortality test estimated a LC50 of 1.6 × 104 IU/mg (Bt), in which decreased to 1.5 × 104 IU/mg (Bt and 75 Gy), and 7.7 × 103 IU/mg (Bt and 125 Gy). Insect survival was prolonged for both individual and simultaneous treatments. The ratio of males was 3.5-fold to females in 1.5 × 104 IU/mg and 75 Gy, while threefold of males to females was recorded in the treatments of 3.75 × 103 IU/mg and 75 Gy, 7.5 × 103 IU/mg and 75 Gy, 7.5 × 103 IU/mg and 125 Gy and 1.5 × 104 IU/mg and 125 Gy. Results of fecundity, fertility and sperm transfer of F1 males were significantly lowered in irradiated insect combined with Bt than individual treatment. Conclusion Gamma irradiation treatment combined with Bt concentrations achieved a high reduction of S. littoralis, and the toxicity effect of Bt increased as compared with individual treatments taking advantage as compatible control tactics. Simultaneous treatment of IST and Bt could be considered as a competent approach for S. littoralis population suppression.

Keywords

• Inherited sterility technique
• Bacillus thuringiensis
• Spodoptera littoralis
• Gamma irradiation
• Biocontrol