This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This small fly, which belongs to the family Cecidomyiadae, causes very great loss by its maggots destroying the young pears. Although it has been known for many years it has increased enormously of late, and in some parts of Britain the greater part of the crop is destroyed by it.
The damage is done by the small white maggots feeding inside the young pears. The infested fruitlets are very marked, they become abnormally swollen and deformed and make rapid growth compared with sound fruitlets. The infested fruitlets (known as "bottlers" in the trade) are found to be black inside when cut open and to contain as many as fifty maggots, which when mature reach 1/7 in. long (fig. 359).
The adult fly appears when the Pear blossom just shows the " white cap stage". The female is only 1/8 in. long, the male 1/10 in.; the latter is a dark blackish-grey, two-winged midge with yellow hairs on the thorax. The wings have few veins and are dusky with fine black hairs, the halteres yellow. The female has a long ovipositor, by means of which she lays her ova deep in the unopened blossoms.
The mature maggots either fall from the fruit-lets, which may crack, or the fruitlets may fall to the ground and decay - in either case the larvse enter the soil and pupate there, remaining beneath the trees until the following spring, at a depth of 1 to 2 1/2 in.
All infested fruitlets should be picked off in May or early June, and destroyed with the maggots in them. Surface soil may be removed in winter to a depth of 3 in. and burnt or buried, or replaced by fresh soil. Spraying has no effect on this fruit pest. The use of the hoe during the summer months would expose the chrysalides to the birds.