The effectiveness of Samia ricini Drury (Lepidoptera: Saturniidae) and Attacus atlas L. (Lepidoptera: Saturniidae) cocoon extracts as ultraviolet protectants of Bacillus thuringiensis for controlling Spodoptera litura Fab. (Lepidoptera: Noctuidae)

Bacillus thuringiensis var. kurstaki (Bt.) is a bioinsecticide that is often used as an alternative for controlling tobacco cutworm, Spodoptera litura Fab. (Lepidoptera: Noctuidae). However, this bioinsecticide might easily degraded by ultraviolet (UV) from the sun light. This study aimed to determine the effectiveness of eri, Samia ricini Drury (Lepidoptera: Saturniidae) and atlas moth, Attacus atlas L. (Lepidoptera: Saturniidae) cocoon extracts as UV B protectants for Bt. against the larval stage of tobacco cutworm. Cocoon extracts of 0, 0.5, 1, 2, and 2.5% of eri and atlas sericin was added respectively to make Bt. suspensions at 10LC(95) (2 x 10(8) spores/ml). After that, the suspensions then exposed under UV B lights at laboratory conditions for 1, 2, 3, and 4 weeks. Then, the pathogenicity was tested against 25 individuals of 1st larval instar of tobacco cutworm using three replicates. The results showed that the mortality percentage of tobacco cutworm treated with cocoon added Bt. were significant difference compared to Bt. alone. At the 1st week of UV B exposure, the mortality of tobacco cutworm in Bt. alone, Bt. + eri, and Bt. + atlas was 31.67, > 90, and > 75% respectively. Whereas, at the 4th week, the mortality of each treatment was 46.67, > 81, and > 75% respectively. The pathogenicity results implied that the addition of eri and atlas silk moths cocoon extracts significantly improved the Bt. toxicity by 1.75 - 1.86 and 1.6 - 2.1 fold, respectively, even after four weeks of UV B exposure. Based on this research, it can be concluded that the addition of eri and atlas silk moths sericin extracts show high potential for the UV B protectants for Bt. to enhance its persistence for future formulations.