A Life-history Study of Endrosis lactella (Schiff.) (Lep. Oecophoridae)

Abstract

Endrosis lactella is widely distributed in Britain, where it is a minor pest of stored products, especially of grain and seeds.The incubation period of the egg varied between 42 days at 10°C. and 6·0 days at 26°C. It was almost unaffected by changes in relative humidity.Survival of eggs was low at high temperatures and low humidites, and the mean survival from complete batches of eggs at 70 per cent. R.H. 25°C. was 44 per cent. The highest survival recorded was 81 per cent.On a diet of middlings the larval stage lasted 133 days at 90 per cent. R.H. 10°C, and 38 days at 90 per cent. R.H. 25°C. No adults were reared from larvae grown below 80 per cent. R.H. At 90 per cent. R.H. and 25°C. there were 7 instars.On various foodstuffs at 90 per cent. R.H. 20°C, duration of the larval stage varied between 40 days on dead moths and 109 days on macaroni. Survival to the adult stage varied between 75 per cent. on whole wheat and 20 per cent. on groundnuts.The pupal incubation period was 58 days at 10°C. and 10·4 days at 25°C, and was approximately the same at all humidities.The time required for complete development from egg to adult was 235 davs at 10°C. and 62 days at 25°C. (90 per cent. R.H.).There was a significant correlation between the weight of a female moth at emergence and the number of eggs laid. Egg output was lower at 25°C. than at 15°C, was not significantly affected by relative humidity, but was increased by provision of drinking water. Weights of females varied from 2·9 mg. to 9·4 mg. and egg output from 14 eggs to 231 eggs.The sex ratio of the adults in the dried grass culture was found to be 1 male to 23 females.Longevity could not be correlated with weight in all experiments, but, in the case of mated females, was dependent upon temperature, humidity and availability of drinking water. The mean adult life in days was 3–0 at 30 per cent. R.H. 25°C.; 5·0 at 90 per cent. R.H. 25°C.; 9·1 at 90 per cent. R.H. 15°C.; and 8.9 at 70 per cent. R.H. 25°C. + drink. Mated males were very short-lived (2–4 days at 70 per cent. R.H. 25°C).The only important predator was the mite, Cheyletus eruditus, which attacked the young larvae.