Effect of constant light on male sterility in the cotton leafworm Spodoptera littoralis

Females of the cotton leafworm (Spodoptera littoralis) reared in long day c onditions (LD 16:8 h) and mated to males kept throughout the whole period o f development in continuous light (LL) oviposit very small numbers of mostl y sterile eggs. It was found that in control males reared from the first la rval instar in long day conditions there was a large accumulation of eupere ne sperm bundles in their testes on day 1 after imaginal moult. On day 10 o f adult life the number of the sperm bundles was very small. In males kept from the first instar in continuous light there was also high number of spe rm bundles on day 1 after imaginal moult but it did not decrease significan tly on day 10 as was observed in controls. Transfer of different developmen tal stages of S. littoralis from long day conditions to continuous light re sulted in a big difference in the density of eupyrene sperm bundles in thei r testes. In control insects reared through the whole of their development in long day conditions there was a significant decrease in the density of e upyrene sperm bundles on day 10 of adult life. By contrast, in males in con tinuous light, regardless of their developmental stage when transferred, th ere was either no change in density of sperm bundles in day 10 adults or th ere was a significant increase in comparison with day 1 adults. The highest density of eupyrene sperm bundles was observed in day 10 adults when they were transferred to continuous light shortly before moulting to the last in star las day 4 larvae in the last stadium or day 1 pupae). Generally, the d ensity of eupyrene sperm bundles on day 10 of adult development was about 2 -2.5 times higher in males in continuous light then those under long day co nditions. The results presented here indicate that the last larval instar a nd the pupa are the stages most sensitive to constant light treatment, whic h greatly reduces the amount of eupyrene sperm bundles released from the te stes.