Whitefly distribution and cassava mosaic disease occurrence in cassava fields of The Gambia

Abstract

The whitefly Bemisia tabaci is a major insect vector associated with the transmission of cassava mosaic begomoviruses causing cassava mosaic disease (CMD) in Africa. However, information on whitefly populations associated with cassava fields in The Gambia remains limited. This study aimed to investigate the whitefly abundance and its association with CMD incidence in major cassava growing regions of The Gambia. Field surveys were conducted in 44 cassava fields across the West Coast Region (WCR), Lower River Region (LRR), and North Bank Region (NBR) following the harmonized West and Central African Virus Epidemiology protocol. Whiteflies were counted on the top five leaves of sampled cassava plants, while CMD incidence was determined based on the proportion of plants showing characteristic symptoms. Whitefly populations were generally low across surveyed regions, with an overall mean abundance of 21.1 whiteflies per plant. The highest mean whitefly abundance was recorded in LRR (36,6), followed by the NBR (19) and WCR (14). Despite widespread CMD occurrence, no consistent association was observed between regional whitefly abundance and CMD incidence. Assessment of probable infection pathways based on symptom distribution showed 94.5% of CMD affected plants exhibited symptom patterns consistent with cutting borne infection, while 5.5% showed patterns consistent with whitefly-transmitted infection. The findings suggest that infected cassava planting materials may currently contribute more substantially to CMD dissemination than whitefly-mediated spread in the surveyed areas. This study provides baseline information on whitefly abundance and CMD occurrence in cassava fields of The Gambia and supports future vector surveillance and disease management strategies.