The effects of rearing conditions on the immature stages and adults ofSpodoptera littoralis(Boisd.)

Abstract

Some effects on the adult of environmental conditions during the larval and pupal stages ofSpodoptera littoralis(Boisd.) were investigated in the laboratory in Israel. The conditions studied were temperature during larval life, temperature and humidity during pupal life and the density at which larvae were kept, and their effects were found by varying one of them at a time. Except for such variations, larvae were reared in batches of 30–50 at 22–24°C. and 60–70 per cent, relative humidity, pupae were kept at 23–24°C. and 70–80 per cent, relative humidity, and adults were kept in pairs at 20–21 °C. and 75–85 per cent, relative humidity. Larvae were fed on clover leaves and adults on sugar solution.High temperature during the larval stage reduced fecundity; whereas at 22°C. the resultant females laid about 1,200 eggs each and 12·5 per cent, produced non-viable ones only, at 30°C. they averaged about 700 eggs each and 50 per cent, produced non-viable ones only. Temperature during the pupal stage affected fecundity similarly and life-span to a lesser extent; at 20 and 34°C., 40 and 5 per cent, of the resultant adults lived 15 days or more, the percentages of females laying only non-viable eggs were nil and 70 and the mean numbers of eggs laid were about 1650 and 700, of which about 60 and 2 per cent, were viable, respectively. High temperatures were directly inimical to pupae, less than half of which survived at 26°C. or over.The effects of humidity during the pupal stage were in general less than those of temperature. The mean life-span was longest in adults from pupae kept at an intermediate humidity of 76 per cent., as also were the proportion of barren females and the mean number of eggs laid; the percentage of viable eggs was reduced only amongst those from females kept as pupae at over 95 per cent, relative humidity. Pupal mortality was affected only by low relative humidities, which raised it.Larvae reared singly tended to be brighter in colour than those reared in batches of 30–50; fewer died and the subsequent pupae were heavier and longer. The mean life-span of the resultant adults was longer, and they laid more eggs.The results are compared with those of other workers onS. littoralisand other insects.