Abstract
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 × 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.