Effects of sublethal dose of chlorfluazuron on ovarian development and oogenesis in the common cutworm Spodoptera litura (Lepidoptera : Noctuidae)

Sublethal doses of chlorfluazuron (LD10: 1.00 ng per larva or LD30: 3.75 ng per larva) topically applied on newly molted fifth instars of Spodoptera l itura (F.) significantly reduced ovarian weight and number of mature eggs i n pupae and adults, compared with those of the controls. The ratios of fres h ovarian/fresh body weight, dry ovarian/fresh ovarian weight, and dry ovar ian/fresh body weight were the same among controls, LD10, and LD30 treated newly emerged adults. In treated adults, the germarium was significantly lo nger than the pedicle and vitelarium compared with those of the controls, w hereas in controls the vitelarium was significantly longer than the germari um and pedicle. This indicates a delayed of maturation of ovarioles in trea ted cutworms. These doses also disrupt growth and development of oocytes by significantly affecting the size of basal oocytes and thickness of follicu lar epithelium. The maximum size of basal oocytes recorded on the day of ad ult emergence was significantly reduced in LD10 or LD30 treated females, co mpared with those of the controls. Thr thickness of the follicular epitheli um of basal oocytes reached to a maximum in the controls on the eighth d an d in treated females on the ninth d after pupation. In newly emerged treate d adults, the protein content of ovaries was significantly reduced but the carbohydrate and lipid contents were not significantly affected, compared w ith those of the controls. The effects of chlorfluazuron on ovarian develop ment and oogenesis are presumed to be responsible for the reduction in fecu ndity caused by sublethal exposure to chlorfluazuron.