Xanthomonas campestris pv. musacearum insect vector activity on banana across altitude and seasons in Rwanda

Banana Xanthomonas Wilt (BXW) ( Xanthomonas campestris pv. musacearum -Xcm) disease is considered the most important threat to banana production in the Great Lakes Region of Africa. Insect vectors are one of the key ways through which the disease is transmitted. This study sought to determine the effect of altitude and season of year on Xcm insect vector activity in Rwanda and also whether nectar volume and sugar content influence vector activity. Insects found foraging on banana flowers were collected from areas representing low (800-1400m), medium (1450-1650m) and high (1700-2200m) altitudes. Data were collected 4 times in 2012 representing short dry, short rainy, long dry and long rainy seasons. Insects were sampled in the morning (7:00 am – 9:00 am), mid morning (10:00 am – 12:00 noon), early afternoon (1:00 pm and 3:00 pm) and in the evening (4:00 pm and 6:00 pm). Seventeen insect species were associated with banana flowers; out of these, Xcm was isolated from four (fruit flies, bees, flies and wasps). Insects were more active during mid morning and early afternoon and more prevalent in the low altitude areas and in the long rainy season. Beer and dessert bananas had significantly (P<0.01) higher nectar sugar content; attracted more insects and were the most affected by BXW. The highest percent sugar content (32%) was recorded in the dry season in low altitude areas. Nectar volume was highest in the long rainy season which also corresponded with both vector activity and high disease incidence. It was concluded that BXW incidence increases with prevalence of insect vectors and these seemed to be attracted by nectar availability and sugar content. As such, banana varieties with non-persistent male bud bracts were very susceptible to BXW. It was therefore, recommended that timely and regular removal of male buds be encouraged and that banana varieties with persistent bracts be promoted in a bid to minimize damage of banana by BXW.