Wheat Bulb fly, Delia coarctata, is a small fly which lays its eggs in exposed soil in July and August. These eggs hatch from January to March the following year, depending on soil temperatures. Once hatched the larvae move through the soil and bore into the base of cereal plants feeding on the central shoot. This causes the characteristic dead-heart symptoms to appear. Although the outer leaves remain green during early stages of attack plants become dull in appearance and, unless examined carefully, the attack may go unnoticed until dead-hearts become visible in February or March.
Winter wheat, winter barley, rye and early sown spring wheat can all be attacked. Crops that have not started to tiller before they are attacked can be destroyed completely. Spring wheat and spring barley drilled December to March can be killed before emergence. Traditionally the main risk area is eastern England where Wheat Bulb fly is a major pest of winter wheat. Yield losses depend on pest numbers, plant populations and other factors, but a guide is a potential loss of 0.7 tonnes per hectare if 20% of plants are attacked.