Bioactivity of a bacillus thuringiensis cryiac toxin to spodoptera litura bioaktivitas toksin bacillus thuringiensis cry 1 ac terhadap spodoptera litura

ABSTRACT The transgenic cotton expressing Bacillus thuringiensis toxin CrylAc in Indonesia has been planted since 2000 for controlling Helicoverpa armigera_ Spodoptera litura is another lepidopteran insect that also attacks cotton. The objective of this research was to determine the toxicity of CrylAc to S. litura. The acute toxicity was determined using neonates of S. litura exposed to artificial diets treated with series concentrations of CrylAc Ac ranging from 0.14 to 625 mg,/ml, and larval mortality was recorded at the seventh day after treatment. The chronic toxicity was determined by exposing neonate to artificial diets treated with the sublethal concentrations (LC5 and LC p). The growth and development of treated larvae were compared with those of the control larvae. CrylAc was toxic to neonate with LC5 values of 71.9, 18.1, 24.7, and 16.2 mg/ml for S. litura collected from Wonosari, Bantul-1, Bantu°l-2, and Kopeng, respectively. CrylAc was more toxic than formulated B. thuringiensis (LC59= 724.8 mg/m1). Larvae exposed continuously� to artificial diets treated with sublethal concentrations of CrylAc (0.61 and 9.77 mg/ml) showed no significant difference on weight and length of each life stages than those of the control larvae. These indicate that the application of the tested sublethal concentrations of CrylAc did not affect the growth and development of S. litura. However, increasing concentrations of Cry I Ac (156.25 and 625 mg/m1) significantly reduced the weight of surviving larvae. These findings suggest that application of CrylAc to S. litura shows some toxicological effects. The effectiveness of the transgenic cotton in controlling S. litura in field situation will be discussed. Key words: Bacillus thuringiensis, CrylAc, Spodoptera litura INTISARI Kapas transgenik yang mengekspresikan toksin CrylAc Bacillus thuirngiensis telah ditanaman di Indonesia untuk mengendalikan Helicoverpa armigera. Spodoptera litura adalah Lepidoptera lain yang juga menyerang pada tanaman kapas. Penelitian in bertujuan ntendeterminasi toksisitas toksin CrylAc terhadap larva S. litura. Pengujian toksisitas akut dilakukan dengan memberi makan larva yang baru menetas dengan pakan buatan yang telah diperlakukan dengan toksin konsentrasi 0,14-625 mg/ml, dan mortalitas larva dihitung satu minggu setelah aplikasi. Toksistas kronik dideterminasi dengan memberi makan larva dengan pakan yang telah diperlakukan dengan konsentrasi sublethal (LC, dan LC4). Pertumbuhan dan perkembangan larva yang diperlakukan dibandingkan dengan larva kontrol. Nilai LC,0CtylAc adalah 71,