Phytomyza gymnostoma

Phytomyza gymnostoma Loew, 1858

At present, the male genitalia in combination with the host plant are quite distinctive to separate gymnostoma from other agromyzids of economic importance. However, variability of the male terminalia and other characters suggest that gymnostoma in fact consists of a group of distinct species (von Tschirnhaus personal communication).
The shape of the aedeagus somewhat resembles Chromatomyia species.

Wing length: 2.8 - 3.5 mm. Body generally dark, mat. Head extensively yellow, frons and ptilinum yellow, occiput and orbits dark. Eyes relatively small and roundish, genae and frontorbits large. Halteres white, squamae without dark margin, tegulae yellowish. Legs dark with yellow knees.
Male terminalia
Aedeagus illustrated in Phy gymnostoma aed lateral.pct, Phy gymnostoma aed ventral.pct. Epandrium with articulated surstyli, that should be visible without dissection of male genitalia (Phy gymnostoma epandrium.pct).
Immature stages
Puparium dark brown, posterior spiracles each with irregular 18-20 bulbs.

Since Phytomyza gymnostoma only a short time ago became a pest species, there is not much information available on the biology and ecology of this species: Oviposition takes place in the leaf, the emerging larva feeds downward into the root. Pupation takes place in the mine, preferably near the soil. In the winter, the puparia can be therefore found in the soil litter. There are two generation per year, in Rhineland (Germany) adults were observed in April/May and again in September/October (Burghause, 1998).

Allium cepa (onion), Allium porrum (leek), Allium sativum (garlic) possibly also other Allium species.

Widespread in Europe, Known from Austria, The former Czechoslovakia, Denmark, Finland, France, Germany, Hungary, Italy (Sicily), Poland, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkmenia, Ukraine.

Phytomyza gymnostoma was not included into the monograph about Agromyzidae of economic importance by Spencer, 1973. At that time also the biology of this fly was not known. A number of recent articles and internet reports (Burghause, 1998, Billen, 1999) reporting severe infestations of Allium especially in Central Europe. Up to 10 eggs were observed on a single plant (Burghause, 1998). The economic loss can be serious both because of actual feeding damage and because minor feeding traces can render onions or leek almost unmarketable.
The observations suggest that gymnostoma must be considered as new important pest on onion and leek. An increasing significance has to be expected.