AN INSECT, AGRONOMIC AND SOCIOLOGICAL SURVEY OF GROUNDNUT FIELDS IN SOUTHERN AFRICA

An intensive survey of the insects in groundnut fields in Malawi, Zamb ia and Zimbabwe was carried out in the 1986-1987 production season. Le ss intensive surveys were also made in Tanzania and Botswana. Agronomi c and socio-economic details of approximately 100 farms were collected simultaneously. The insect survey concentrated on soil insects. White grubs (scarabaeid larvae) were the predominant taxon and were likely to be causing considerable reductions in crop yield. About 40 species of the former were collected. They were followed in order of importanc e by termites. Pod borers (elaterids, tenebrionids, doryline ants and millipedes) were generally present but rarely at sufficient densities to warrant concern. Hilda patruelis was encountered in high densities when crops had been sown too early. White grubs were most likely to be encountered in areas of intensive agriculture, where rainfall exceede d 1000 mm year-1 and where soils were sandy or loamy. Termite damage w as associated with drought, mainly at the end of the growing season. I t was especially severe in Botswana. Insect pest management options sh ould be restricted to high risk areas. Insecticides should be applied only to the preceding maize crop because of the risk of seed-oil conta mination. Experimentation on other management options for the soil ins ects may demonstrate the benefits of fallowing and growing economicall y viable cleansing crops. Foliage feeders were apparently of no econom ic importance except where insecticides had been applied (entirely a r esearch station activity). Aphis craccivora, the vector of groundnut r osette virus (GRV), was apparently controlled by natural processes. Th e low incidence of GRV in the region may be caused by early (and synch ronous) sowing. The economic survey indicated that groundnut crops gen erated cash to a level that would enable farmers to purchase the input s needed to give future groundnut crops a considerable boost in yield.