One of the worst pests of pear trees is the pear midge, known as Diplosis pyrivora or Cecidomyia nigra, the females of which lay their eggs in the flowerbuds before they open.
The fungus infects young canes through wounds which are initially caused by raspberry cane midge attack, late spring frosts or pruning.
As a rule flies are of small or moderate size, and many, such as certain blood-sucking midges of the genus Ceratopogon, are even minute; as extremes of size may be mentioned a common British midge, Ceratopogon varius, the female of which measures only 14 millimetre, and the gigantic Mydaidae of Central and South America as well as certain Australian robber-flies, which have a body 1-11n.
The best-known dipterous pests are the Hessian fly (Cecidosnyia destructor), the pear midge (Diplosis pyrivora), the fruit flies (Tephritis Tyroni of Queensland and Halterophora capitata or the Mediterranean fruit fly), the onion fly (Phorbia cepetorum), and numerous corn pests, such as the gout fly (Chloropstaeniopus) and the frit fly (Oscinis frit).
Ritter (1890) have since observed a similar early origin for the germ-cells in the midge Chironomus and in the Aphidae.
