Assessing interactions between wild host plants and stemborer species in East Africa

Abstract Lepidopteran stemborers are among the most destructive pests of maize, sorghum, and sugarcane in Africa. Yet, data on their species composition and host range in Rwanda remain limited. This study provides the first comprehensive assessment of stemborer diversity, seasonal dynamics, and altitudinal distribution across eastern (low altitude), central (mid-altitude), and northern (high altitude) Rwanda. Surveys were conducted during both the rainy (maize growing) and dry seasons of 2023–2024, targeting infested maize fields and surrounding wild vegetation. A total of 2691 stemborer individuals were recovered from nine host plants, with 1474 (54.8%) from wild and fodder vegetation and 1217 (45.2%) from maize plantations. Species richness was highest in the mid-altitude zone, while overall abundance peaked at low altitudes. Busseola fusca was the most abundant in the high-altitude zone, Chilo partellus in the low altitude, and Sesamia spp. was concentrated in the mid-altitude. Seasonal variation significantly influenced population dynamic, with the highest abundance (1251; 46.4%) recorded during the dry season. Notably, Pennisetum purpureum (Napier grass) hosted 1156 (42.9%) of all specimens, highlighting its role as a key refugium during maize off-seasons. These findings underscore the ecological importance of wild vegetation in sustaining stemborer populations and suggest that wild vegetation, altitudinal, and seasonal factors must be considered in designing integrated lepidopteran stemborer pest management strategies.