Location, agricultural landscape and time affect the occurrence, pest status and control of Phthorimaea spp. on potato and tomato in South Africa

The Phthorimaea spp. complex consisting of the Potato tuber moth, Phthorimaea operculella (Gelechiidae) and tomato leafminer, Phthorimaea absoluta (Gelechiidae) are important pests of solanaceous crops. These two species differ in their preference for crops, with P. operculella being the major pest of potato while P. absoluta is most important on tomato. In South Africa, the production areas and pest complex overlap on these two crops and the insecticides used for their control are similar. The recent change observed in Phthorimaea spp. composition in potato fields is of concern to producers in regions where both crops are planted. The potato and tomato industries in South Africa are heavily reliant on insecticides for pest control, and control failure of both these pests occurred. This study monitored the presence of Phthorimaea spp. larvae in potato fields, their susceptibility to insecticides, and the distribution patterns of moths inside and in natural veld adjacent to potato fields. Above-ground larval infestation of P. absoluta in potato can be as high as 99% depending on the location, agricultural landscape and time during a cropping season. Moth trap catches along a gradient from within potato fields up to 100 m in the natural vegetation changed according to the crops present and time during the cropping season. Resistance to insecticides by both Phthorimaea spp. was confirmed in laboratory assays. A holistic approach that considers the different species, crops and control options is therefore important for sustainable Phthorimaea spp. management, on solanaceous crops in South Africa.