Like most other insects, Chilo partellus requires sterols such as cholesterol in the diet. Freshly hatched larvae grown on a chemically defined diet take about 27 days to become adults. However, when an azasteroid, 25-azacholesterol is added to the diet in concentrations ranging from 0.5 ppm to 25 ppm, the time taken to become adults became 41 days at 5 ppm azasteroid. The maximum larval weight decreased to 76 mg from 140 mg as compared to the control insects. In larvae reared on a diet with 10 ppm azacholesterol, about 60% larvae died. The mortality was almost complete at a dose of 25 ppm. The larvae, pupae and adults reared on the chemically defined diet contained sitosterol, stigmasterol, cholesterol, compesterol and isofucosterol. No desmosterol was, however, detected in these insects. Inclusion of 25-azacholesterol in the diet led to the detection of desmosterol in these insects. It was observed that the cholesterol concentration decreased greatly, whereas sitosterol and stigmasterol concentration increased. This showed that the azacholesterol inhibited the dealkylation of C29 plant sterols to cholesterol, probably at the level of Δ-24-sterol reductase as evidenced by the accumulation of desmosterol. In some cases the adults were unable to separate themselves completely from the pupal cases. Some larval-pupal intermediates were also noted. It was further observed that the spermatogenesis was disturbed due to azacholesterol treatment. This may indicate that ecdysone biosynthesis is probably impaired. These results indicate that inhibition of steroid utilization may have the potential of being developed into a method for integrated pest management.
When 1, 2-dibenzoyl-1-tert-butylhydrazine was added to the diet at concentrations varying from 1 to 10 ppm, all the larvae died in all the concentrations tested, except 1 ppm. The larval weight was reduced to almost half due to the treatment and the larval duration increased as in case of 25-azacholesterol. However, the sterol composition of the insects did not change greatly.
