Investigations of the chemical control of insect pests of cotton in central Africa. II.—Tests of insecticides with larvae and adults

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Abstract
Further tests of insecticides, mainly carbaryl, endosulfan, endrin and DDT, for possible use against pests of cotton in Central Africa are described. In laboratory tests in Rhodesia, carbaryl was the most effective against first-instar larvae of Diparopsis castanea Hmps. exposed on leaves, stems and bracts of effective against second-instar larvae of Heliothis armigera (Hb.), to which the insecticides were applied directly, and carbaryl the least.When adults of Dysdercus intermedius Dist. and D. fasciatus Sign. were caged with treated bolls, carbaryl was the most effective, endrin the next and (against the former sp. only) endosulfan the least. Deposits on leaves from 0.5 per cent. sprays of carbaryl, DDT and endosulfan remained effective in dry conditions for two weeks, but application of 0.05–1.0 in of simulated rain reduced their effectiveness immediately, especially that of carbaryl. The effectiveness of deposits was also reduced by plant growth and was affected by plant habit; on a hairy variety the deposits persisted longer than on a glabrous one, partly because the hairs retained them and partly because they made movement of the larvae more difficult.