An insect, agronomic and sociological survey of groundnut fields in southern Africa.
An intensive survey of the insects in groundnut fields in Malawi, Zambia and Zimbabwe was carried out in the 1986-87 production season. Less intensive surveys were also made in Tanzania and Botswana. Agronomic and socio-economic details of approximately 100 farms were collected simultaneously. The insect survey concentrated on soil insects. 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 importance 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. Scarabaeids were most likely to be encountered in areas of intensive agriculture, where rainfall exceeded 1000 mm/year and where soils were sandy or loamy. Termite damage was associated with drought, mainly at the end of the growing season. It was especially severe in Botswana. Insect pest management options should be restricted to high risk areas. Insecticides should be applied only to the preceding maize crop because of the risk of seed-oil contamination. Experimentation on other management options for the soil insects may demonstrate the benefits of fallowing and growing economically viable cleansing crops. Foliage feeders were apparently of no economic importance except where insecticides had been applied (entirely a research station activity). Aphis craccivora, the vector of groundnut rosette virus (GRV), was apparently controlled by natural processes. The low incidence of GRV in the region may be caused by early (and synchronous) sowing. The economic survey indicated that groundnut crops generated cash to a level that would enable farmers to purchase the inputs needed to give future groundnut crops a considerable boost in yield.