Coconut shell and straw charcoals to protect bacillus thuringiensis against ultraviolet b and sunlight to control tobacco Armyworm, Spodoptera litura (Fabricius, 1775) (Lepidoptera: Noctuidae)

Abstract

Crops, for examples tobacco, onion, chili, and Brassica, in Indonesia are vulnerable to the attack of the tobacco armyworm, Spodoptera litura Fabricius (Lepidoptera: Noctuidae). The use of synthetic insecticides become the major component of tobacco armyworm control. Bacillus thuringiensis (Bt) is an effective biological control agent; however, it is easily deteriorated by the ultraviolet lights from sunlight. The aim of this research was to investigate the coconut shell and straw charcoals as ultraviolet B (UVB) and sunlight protectants for Bt as a biological agent for controlling tobacco armyworm. Charcoal extract solutions (2% w/v) were made and used for Bt formulations, then exposed under UVB lights in the laboratory for 0, 72, and 144 h as well as exposed under sunlight for 0, 1, 3, 7, 14, 21, and 28 d. The formulations were then tested against one-day-old 1st larval instar of tobacco armyworm. The results showed that Bt added with coconut shell and straw charcoals at two days after treatment of UVB had higher pathogenicity compared to Bt alone. The larval mortality in each treatment was >82, >85, and <60% ,respectively. The mortality of tobacco armyworms between the coconut shells (100%) and straw (93.6%) charcoals after 28 days of sunlight treatment was not significantly different. This study suggested that coconut shell and straw charcoals gave good protection to Bt from UVB and sunlight.