PEST COMPLEX IN AGROFORESTRY SYSTEMS - THE MALAWI EXPERIENCE

A survey of insect species associated with multipurpose trees and Phaseolus beans in an agroforestry research field and tree nursery was conducted from October to December 1988 and January to February 1989 and 1990 at Makoka Agricultural Research Station. Eleven insect species belonging to 11 genera were collected and identified. A further four heteropteran and two lepidopteran species have not yet been identified. A leaf beetle, Mesoplatys ochroptera (Stal.), caused severe defoliation of Sesbania spp. and an unidentified lepidopteran caterpillar species fed gregariously on Sesbania spp., also causing considerable defoliation. In February 1991 a severe outbreak of the scale insect, Macropulvinaria inopheron (Laing), occurred on six species of multipurpose trees and on Cajanus cajan (L. ) growing in the surrounding home gardens. Some of the pest species found feeding on the multipurpose trees are also known to cause minor or occasional economic damage to field crops. The remainder of the species are either of no known pest status or natural enemies of other fauna. The purpose of agroforestry systems and the likely effects of such systems on pests and disease are outlined. Some of the factors that are likely to influence pest severity and may be altered by crop/tree mixed cropping systems are also described. Past research findings on the effects of mixed cropping on pest incidence and damage to crops are reviewed. Economic implications of the occurrence of an important multipurpose tree and/or field crop pest in an agroforestry system have also been examined to illustrate the need to incorporate some aspects of pest management in agroforestry research programmes.