Effects of sublethal doses of chlorfluazuron on the ovarian biochemical constituents of Spodoptera litura

Abstract

This paper describes the effects of sublethal doses (LD₁₀: 1.00 ng larva^-1; LD₃₀: 3.75 ng larva^-1) of chlorfluazuron on the amounts of ovarian constituents during various stages of development in common cutworm, Spodoptera litura (F.). Chlorfluazuron was applied topically to newly ecdysed fifth instars under laboratory conditions. In newly emerged adults, the amount of ovarian protein in LD₁₀ and LD₃₀ treated larvae was significantly reduced, but carbohydrate and lipid were not affected compared with their respective controls. The order of relative proportion of the amount of ovarian DNA in three developmental stages was: newly emerged adults>newly pupae>newly ecdysed larvae. Moreover, the order of the amount of RNA was: newly ecdysed larvae>newly emerged adults> newly pupae. The amount of utricular DNA was greater (14.2 μgmg^-1 of tissue) after first mating than the second one in the spermatheca. However, the amount of ovarian DNA was reduced more than ovarian RNA and it decreased rapidly, whereas amount of DNA decreased steadily. On the 5th day of pupae, ecdysteroid titer was 3.5 ± 0.8 pgmg^-1. Initially, it was increased slowly then gradually, and furthermore, sharply during the 5th day of pupae to before adult emergence. It was peaked on the 1st day after adult emergence (52.0 ± 1.5 pgmg^-1) and decreased thereafter. Therefore, it is concluded that sublethal doses of chlorfluazuron reduced the amounts of ovarian constituents during ovarian development and oogenesis in S. litura. These reductions increased with an increase in dose from LD₁₀ to LD₃₀. The effects of chlorfluazuron on the amounts of ovarian constituents are presumed to be responsible for the reduction in fecundity caused by sublethal exposure to chlorfluazuron.

Key words: Chlorfluazuron, ecdysteroid, nucleic acids, oogenesis, Spodoptera litura, sublethal doses.