Plants affected
Most pear cultivars are attacked, particularly those that
flower mid-season. Early- and late- flowering cultivars are
less susceptible.
Symptoms
Infested pear fruitlets grow and swell more rapidly than normal fruits initially. However, a few weeks after petal fall in mid-May/June these enlarged fruitlets blacken and then fall from the tree. Such fruitlets contain many yellow-white maggots up to 4mm long, but they may already have left the fruitlets by the time they drop from the tree. In some years a very large proportion of the potential crop can be lost.
Biology
The adult midges are tiny flies that lay eggs in the unopened flower buds. The larvae develop inside the fruitlets and feed for about a month. They leave the fruitlets in early summer and crawl into the soil, where they overwinter in cocoons and pupate in the following spring. Adults emerge in April/May.
Control
Pick and dispose of infested fruitlets before the maggots leave.
Bifenthrin (Scotts Bug Clear Gun, Bayer Sprayday Greenfly Killer Plus or Doff All-In-One Garden Pest Killer) can be applied at the white bud stage (i.e. when the petals can be seen but before the flowers have opened) to kill the adults, before they can lay eggs. Spraying is only feasible on trees that are small enough to be treated thoroughly. Never spray when the flowers are open as insecticides will harm bees and other pollinating insects.