A study in East Africa of the bean flies (Dipt., Agromyzidae) affecting Phaseolus vulgaris and of their natural enemies, with the description of a new species of Melanagromyza Hend

Abstract

Examination of infested bean plants (Phaseolus vulgaris) showed that “bean fly” in East Africa consists of three species, Melanagromyza phaseoli (Tryon), M. spencerella sp. n. and Ophiomyia centrosematis (de Meij.). M. spencerella is described, and notes are given on the life-cycle, host-plants and distribution for all three species. Their importance in East Africa is discussed and it is concluded that M. spencerella is the most damaging because it oviposits and feeds in the hypocotyl, is frequently the most abundant species and is less effectively parasitised. Bean plants able to produce adventitious roots freely are able to grow away from the important early attack in the stems. Published work on chemical control measures is summarised.The parasite complex associated with bean fly in East Africa was studied, and notes are given on the species present, the recognition of their early stages, their host ranges and abundance. Parasitism is discussed in relation to the infestations found on beans, with special reference to Opius melanagromyzae Fisch., the most important parasite of M. phaseoli, and Eucoilidea sp., the most important parasite of M. spencerella. It is concluded from graphical analysis that O. melanagromyzae is density-dependent and an important factor in limiting M. phaseoli populations in East Africa. Eucoilidea sp., on the other hand, shows signs of delayed density-dependence and is less effective in controlling its principal host. O. melanagromyzae has recently been sent to Hawaii for release against M. phaseoli; some field recoveries have been made already.