Bean fly
Ophiomyia phaseoli

The most serious damage by adults occurs when plants are at the unifoliate stage. The unifoliate leaves show a large number of feeding and oviposition punctures on the upper side with corresponding light yellow spots, especially on the basal portion of the leaf. The first and second trifoliate leaves show some egg holes, but leaves situated above this are practically undamaged. Larvae feeding soon after hatching produce numerous larval mines which are better seen on the underside of the leaves just under the epidermis, and appear as silvery, curved stripes; on the upper side of the leaf only a few tunnels are visible. Later, both egg holes and larval mines turn dark brown and are clearly visible. In cases of severe attack, infested leaves become blotchy and later hang down. These leaves may dry out and may even be shed. When mature plants become infested, insect damage is confined to the leaf petioles, which become swollen and at times the leaves may wilt.