Whitefly–Natural Enemy Dynamics and Cassava Mosaic Disease Evaluated Under Field Condition in Sierra Leone

Abstract

Bemisia tabaci is a major pest of cassava in sub-Saharan Africa, causing yield losses through direct feeding and its role in transmitting cassava mosaic disease (CMD). Natural enemies such as lacewings, ladybird beetles, and spiders provide valuable biological control services, yet their interactions with different whitefly developmental stages and plant structural traits remain insufficiently characterized. This study examined the dynamics among natural enemies, whitefly eggs, nymphs, adults, and plant height across 3, 6, 9, and 12 months after planting (MAP) under field conditions. The trial was conducted under natural cassava production conditions during 2020/2021 cropping season at the upland experimental site of the School of Agriculture and Food Sciences, Njala University. A total of 270 cassava genotypes comprising 268 local varieties and 2 improved checks (SLICASS 4 and SLICASS 6) were laid out in an augmented randomized design with four blocks. Results showed that lacewings and spiders strongly tracked nymph and adult whitefly populations, while ladybird beetles showed weaker associations. Principal Component Analysis (PCA) revealed alignment of predators with pest pressure during mid- and late season, whereas plant height exhibited minimal influence. Findings underscore the central role of lacewings and spiders in early and sustained suppression of whitefly populations, highlighting the importance of conservation-based integrated pest management (IPM) strategies. Findings serve as useful guide for conservation biological control as a primary IPM strategy for the enhancement of habitats for effective predators (lacewings and spiders) of the whitefly through reduced pesticide use, ground vegetation retention, intercropping, and maintenance of natural refuge habitats.