Beanfly, Ophiomyia phaseoli (Tryon) and two other agromyzids, O. centrosematis (de Meijere) and O. spencerella (Greathead) are the most destructive pests of snap bean (Phaseolus vulgaris L.) during the seedling stage. The formers two are found in tropical to subtropical regions of Africa, Asia, Australia and the Pacific. The latter species is confined to Africa. Insect larvae feed inside the plant stem which results in severe weakening of and, at times, mortality of the snap bean plant. Insects are more serious during the dry season. The critical period of damage is within four weeks after germination. Certain cultural practices, like ridging seedlings, reduce insect damage. A large number of hymenterous parasites attack all three beanfly species, but these parasites alone cannot control the pests. The present use of broad-spectrum insecticides on commercial farms is not sustainable due to their toxicity to parasites and the development of insecticide resistance in the beanfly species. Newer chemicals with insect growth regulatory (IGR) activity, which are toxic to the pest but safer to parasites, are being developed. Two CIAT accessions, G35023 and G35075, show high levels of resistance to beanfly. An integrated pest control approach, based on the use of a resistant cultivar, seed treatment with insecticides, and occasional use of selective insecticides, will allow full exploitation of natural enemies and has a potential for sustainable control of beanflies. [AS]
