Life-cycle of the tropical warehouse moth,<i>Cadra cautella</i>(Wlk.), at controlled temperatures and humidities

Abstract

The life-cycle of five stocks of Cadra cautella (Wlk.) (Phycitidae) and the duration of the various developmental stages were studied at temperatures from 15 to 37·5°C. and relative humidities between 0 and 100 per cent, on a mixture of wheatfeed, wheat germ and yeast. At 70 per cent. R.H., the limiting temperatures for the completion of the life-cycle were about 15°C. and about 36°C. At 30°C., the limiting humidities were about 20 and above 90 per cent. R.H. Development was quickest at 30–32°C. and 70–80 per cent. R.H., taking 29–30 days from the laying of the egg to the formation of the adult moth. This period increased with lower temperature and humidity, reaching 145·0 days at 15·5°C. (70 per cent. R.H.) and 51 days at 20 per cent. R.H. (30°C.). Near the optimal conditions for rapid development, the egg occupied about 10 per cent, of the developmental cycle, the larva about 70 per cent, and the pupa 20. Temperature influenced the duration of all developmental stages, but humidity had a marked effect only on the larva. The pupation of some mature larvae was delayed: whether or not this delay is a diapause is discussed. Virgin adults lived 4·8 days at 35°C. to 18·9 days at 17·5°C. (70 per cent. R.H.). At 30°C., low humidity halved the length of adult life. The mortality, even in favourable conditions, was often rather high, principally among eggs and young larvae. There was poor survival of small numbers of larvae kept on maize and on cocoa beans, but survival on wheat was similar to that on the usual food mixture. The developmental period on wheatfeed alone was shortened by the addition of honey or glycerine or a combination of wheat germ and yeast. The incidence of disease is discussed.