Influence of alternative plant habitats on cassava whitefly colonisation in Malawi

Abstract

Cassava (Manihot esculenta Crantz) is an important food security and income generating crop in Malawi; whose productivity is constrained by the whitefly (Bemisia spp.) pest complex and associated viral diseases. Current cassava tuber yields in the country are estimated at barely 30% of the potential yield of 91 tonnes per hectare. The objective of this study was to investigate the effect of alternative whitefly host plants within habitats, on whitefly infestation in cassava fields in Malawi. A field study was conducted at Lilongwe and Nkhata Bay in Malawi, in 2017. Treatments included (i) target cassava (<2 months old, and old cassava (8 - 13 months after planting); (ii) natural vegetation; (iii) pumpkin; (iv) sweet potato; (v) beans; (vi) groundnuts; (vii) Irish potato; (viii) soybean; (ix) tobacco and (xi) tomato. Clean sentinel cassava plants were placed in each habitat (three pots per habitat), at the beginning of the growing season. They were collected after four weeks to assess the relative colonisation rates of whitefly, by determining the number of nymphs. Plants placed in the cassava habitats presented the greatest number of nymphs (39.3); followed by natural vegetation (17.8) and old cassava (14.1); compared to other habitats. There were no significant differences (P>0.05) in the amount of parasitism of nymphs between habitats. This study suggests that in diverse landscapes alternative habitats can substantially influence whitefly population dynamics in cassava fields.