Mechanism of Resistance to Bean Fly (Diptera: Agromyzidae) in Soybean

Abstract

Two soybean accessions, PI 227687 and PI 171444, were found to be moderately resistant to bean fly, Ophiomyia phaseoli (Tryon). The resistant accessions have significantly smaller cotyledons and unifoliate leaves; these are the parts of the plant where bean fly lays eggs and the first instars feed. The unifoliate leaves, especially those of the more resistant accession, PI 227687, are pubescent. PI 227687 and PI 171444 hypocotyls, in which the major part of the bean fly larval feeding takes place, are significantly smaller and contain significantly less dry matter than those of the susceptible accession, ‘AGS 66’. Bean fly adults preferred to visit seedlings of ‘AGS 66’ over those of the two resistant accessions, and the insect laid fewer eggs in resistant than in susceptible accessions. Pupae from larvae that were reared on PI 227687 were significantly lighter than those from larvae reared on ‘AGS 66’. Fecundity was drastically reduced when the insects were raised on PI 227687 and PI 171444 when compared with ‘AGS 66’, In addition to morphological characters, certain antibiotic factors seem to be involved in the resistance of PI 227687 and PI 171444 to the bean fly.