Studies of Lygus vosseleri Popp. (Heteroptera, Miridae), a Pest of cultivated Cotton in East and Central Africa

Abstract

Methods have been developed for breeding continuous supplies of Lygus vosseleri in the laboratory. Adults readily oviposit in cotton seedlings, but tend to damage the tissues by feeding, so that the eggs fail to hatch. Portions of developing sorghum heads were found more satisfactory; grains in the milk stage stay fresh long enough for eggs laid in them to hatch, if the ratio of adults to grains is kept low.The method used was to expose sorghum grains to adult Lygus for 3–4 days, afterwards removing the grains to hatching cages to await emergence of nymphs. On emergence, nymphs were transferred to rearing cages and fed immature sorghum grains, changed every two days. Hatching and rearing cages consisted of muslintopped, celluloid cylinders fitting on to shallow tins containing moist vermiculite covered by plaster of paris in which small holes received the sorghum stems.At insectary temperatures the incubation period averaged 8·4 and the nymphal life 16·7 days; adult females survived up to 57 days and production of nymphs per female per day ranged up to 2·95. The mortalty in the egg stage is not yet known:the growth of fungi on the sorghum grains during incubation causes losses. Mortality in the nymphal stages averaged 44 per cent. and occurred chiefly in the first stage, probably due to handling. Improvements to reduce losses are described.Difficulties in maintaining continuous supplies of sorghum grains, caused by attacks of Atherigona on sorghum seedlings and of Contarinia on sorghum heads, can be overcome, respectively by the use of insecticides and by bagging the emerging heads.