Study on the Effect of Allylisothiocyanate Formulations on Three Lepidopterous Insect Larvae, the Diamond Back Moth, Plutella xylostella (L.), the Small Cabbage White Butterfly, Pieris rapae (L.) and Tobacco Cut Worm, Spodoptera litura Fabr

Abstract

Problem statement: The toxicity of seven of Allylisothiocyanate (AITC) formulations, AITC pure and in mixture with cypermethrin and chlorpyrifos, was evaluated using spray application and fumigation method against the diamondback moth, Plutella xylostella (L.), the small cabbage white butterfly, Pieris rapae (L.) and the tobacco cut worm, Spodoptera litura Fabr. Approach: Response varied according to insect species, specific formulation and AITC application rates. Results: Fumigant toxicity of the oil based on 9 h exposure was evaluated against the three insect larvae, the diamond back moth, P. xylostella larvae were more susceptible followed by tobacco cut worm, S. litura and cabbage white, P. rapae larvae. To P. xylostella larvae, LC₅₀ value was 1.5 μL L^-1 air, S. litura larvae (LC₅₀, 1.8 μL L^-1 air) and P. rapae larvae (LC₅₀, 2.0 μL L^-1 air). These three insect larvae were killed after 9 h exposure to a dose of 4.3 μL L^-1 air of the oil, showed no significance difference with that of phosphine (40 μg L^-1 air) a recommended dose. On the other hand, on the spray application bioassays, mortality data counted 72h after treatment, the P. rapae larvae were most susceptible to AITC formulations followed by S. litura larvae and P. xylostella larvae. LC₅₀ values, to P. xylostella larvae, HJ(A) and HJ(B) were the most potent toxicant (33 mg L^-1) and (46 mg L^-1) respectively, while the least toxic was HJ(C) (556 mg L^-1). To S. litura larvae, HJ(B) and HJ(A) were the most efficient (10 mg L^-1) and (22 mg L^-1) respectively, while HJ(D) (LC₅₀, 385 mg L^-1) was found to be the least toxic. The both of HJ (B) and HJ (C) had similar insecticidal activity (LC₅₀, 8 mg L^-1) to Pieris rapae larvae followed by HD (B) (LC₅₀, 22 mg L^-1) and HD (A) (LC₅₀, 82 mg L^-1). Conclusion/Recommendations: It was concluded that the AITC oil showed promise findings and may be a good alternative to old fumigant “phosphine”. The others were found efficient on the spray application bioassays but the mixture of AITC with cypermethrin especially HJ (A) and HJ (B) were found to be better than AITC mixed with chlorpyrifos and AITC pure. So they can be used in the field of crop protection as safer and potential components of an integrated pest management strategy, especially allylisothiocyanate is considered fully biodegradable, less toxic and many cruciferous vegetables daily consumed by humans.