Occurrence of bean fly (Diptera: Agromyzidae) and associated parasitoids in Kenya: farmers' perspectives and management practices.

Outbreaks of bean fly, Ophiomyia spp. (Diptera: Agromyzidae) constitute a major constraint to common bean production in sub-Saharan Africa. Here, we investigate bean fly occurrence patterns, associated parasitoid complexes, and smallholder farmer perspectives across 3 major bean corridors. Three bean fly species [O. phaseoli (Tyron), O. spencerella (Greathead), and O. centrosematis (de Meijere)] were identified. An incidence of 22% to 41% was recorded, mostly associated with O. spencerella, which accounted for up to 57.1% of total species abundance. A diverse assemblage of parasitoids was recorded, with mean parasitism rates of 43.7%, 18.7%, and 32.0% in Kisumu, Nakuru, and Murang'a counties, respectively. Parasitism was primarily driven by Opius sp. (Hymenoptera: Braconidae) (6.7% to 38.3%), followed by Afrostilba sp. (Hymenoptera: Pteromalidae) (2.2% to 28.6%) and Herbertia sp. (Hymenoptera: Herbertiidae) (1.8% to 4.8%). Most farmers recognized typical bean fly damage symptoms, but approximately 75% were unaware that bean flies were the causal agent. Local bean varieties, late sowing, and poor soil fertility were associated with a 17% to 51% likelihood of bean fly outbreaks. Most farmers did not implement any control measures, except in Nakuru County, where nearly 80% relied on broad-spectrum synthetic insecticides [Chlorpyrifos, Duduthrin, Alpha-cypermethrin, and Lambda-cyhalothrin], although this was associated with only a 23% reduction in infestation likelihood. Therefore, targeted awareness campaigns are urgently needed to equip farmers with the basic knowledge for timely diagnosis of bean fly outbreaks. For effective management of bean fly, more research is needed to fully exploit and adopt potential natural enemies to maintain the balance of ecosystems and protect crops without resorting to harmful chemicals.