Abstract
The insecticidal effect of a water-soluble powder of Polyoxin AL, a fungicide that inhibits chitin synthase, on the larvae of Bombyx mori, Mamestra brassicae, Mythimna separata, and Spodoptera litura was examined. After the fungicide was mixed in diet and applied orally, all the larvae of S. litura, M. separata, and M. brassicae died at the molting stage at polyoxin levels of 0.03, 0.1, and 0.3% (wt/wt), respectively. A morphological study with S. litura showed that the larvae to which Polyoxin AL was orally applied failed to form a new cuticle. The median lethal concentration (LC50) of Polyoxin AL in S. litura 3rd stadium larvae was approximately 0.02%. Polyoxin AL had little effect on B. mori, even at 0.3% in the diet. The standard chemicals polyoxin B, polyoxin D, and nikkomycin Z were applied orally to S. litura 3rd stadium larvae. All the larvae were killed after exposure to 0.005% polyoxin B and 0.015% nikkomycin Z. Polyoxin D, however, had no effect even at 0.015%. Polyoxin B and D were injected into the hemocoel of S. litura and B. mori with a syringe. The responses of these insects were quite different. In S. litura, both the chemicals inhibited metamorphosis. In B. mori, polyoxin B inhibited the larval molt, whereas polyoxin D had no effect. Body surface treatment with 1% (wt/vol) Polyoxin AL resulted in a failure to molt in both species.
