Bacillus thuringiensis (Bt) is a biological agent for insect pest management. Its toxins effectively control Spodoptera exigua Hübner (Lepidoptera: Noctuidae) larvae, but it is sensitive to ultraviolet (UV) radiation from the sunlight. This study aimed to investigate the effect of sericin extract from Samia ricini Boisduval (Lepidoptera: Saturniidae) cocoons as a UV protectant for Bt after exposure under direct sunlight for 1, 2, 3, and 4 weeks. After being exposed to sunlight, the Bt formulae were tested against 20 larvae of 24 hr old, the first larval instar in the laboratory. The larval mortality was observed 72 hr after the treatment. The results indicated that the mortality of S. exigua in Bt + sericin extract treatment was significantly different compared with Bt alone. For the first week, the mortality of S. exigua in exposed Bt + sericin exposed Bt alone, unexposed (Bt + sericin, and unexposed Bt alone were 80, 61, 85, and 97%, respectively. Scanning electron microscopy analysis revealed that Bt + sericin, after being exposed to sunlight, still showed the presence of spore and crystal protein comparable to the unexposed Bt. Based on the results, sericin provides good protection against sunlight and prevents the Bt spores from light-induced damage.

Bacillus thuringiensis serotype kurstaki is an entomopathogenic bacteria commonly used to control the cutworm Spodoptera litura (Fab.). However, B. thuringiensis has disadvantage of being easily degraded due to exposed sunlight. The objective of this research was to determine the effectiveness of adding A. atlas (L.) cocoon extract as UV protectant B. thuringiensis to the mortality of S. litura. This research formulated 2.5% of the original substance of A. atlas cocoon extract and B. thuringiensis serotype kurstaki strain HD-7 applied from commercial product DiPel-WP®. The formulation was exposed to sunlight for 0, 1, 2, and 3 weeks. The suspension treated for 20 individuals of first instar larvae S. litura shifted into the artificial diet using 3-5 replicates. The scanning electron microscope (SEM) method began from a sample that was vacuumed, sample coated, and observed on SEM with the electron in a certain level probe. This research showed that the mortality of S. litura decreased with the growth of S. litura. The mortality of S. litura achieved 20%-100% mortality after treatments. The A. atlas cocoon extract was effective as UV protectant B. thuringiensis for three weeks of exposure to sunlight. The SEM analysis represented that formulation of B. thuringiensis and A. atlas cocoon extract sunlight exposure for one week has harsher surface than exposed during three weeks.

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