Genus Agromyza

Agromyza Fallén, 1810

Next to the phytomyzine Genus Nemorimyza, this taxon is the agromyzid group with the most plesiomorphic characters. Yet it can be easily recognized by the presence of stridulation organs on the edges of the first two abdominal tergites present in both sexes (von Tschirnhaus, 1972) (Ag albipennis strid file.pct, Ag intermittens strid file.pct). For more information see the section External adult morphology.

Stridulation organs present at the lower margin of the first abdominal tergite. Spencer, 1976 or 1986 added some diagnostic characters which are only valid in combination: Subcosta complete, joining R1 before reaching costa; halteres white and yellow (darker in a few tropical species) orbital setulae reclinate; either 3+1 strong dorsocentral or 3 or more post-sutural dc, pre/scutellars present; costa ending a R4+5 or continuing to M1+2, in most species second cross/vein present.

Male terminalia
Epandrium with fused surstyli, which are often bent downwards. Cerci elongated and normally narrow (Ag frontella epandrium.pct, Ag megalopsis epandrium.pct), apparently with clasping function. Gonites long, at basal part tightly connected with aedeagal apodeme, distal part of gonites rather flat, not stick-shaped. In expanded position the basal part forms a conspicuous loop (Ag albipennis genitalia.pct, Ag nigrella genitalia.pct). Basiphallus usually broad with distinct lateral sclerites. Bridge between side sclerites of basiphallus either missing or closely connected with the basal vesica of distiphallus. Frequently a single appendage branching from the base of basiphallus can be found.
In most grass mining Agromyza species, distiphallus often 's'-shaped in lateral view. The two terminal tubules almost always well visible. They are broad in the group of monocot feeding species (except Agromyza cinerascens and relatives), from side view about as broad as basal vesica (Ag nigrella aedeagus.pct), sometimes funnel shaped. Most species of economic importance belong to this group. In other species groups the terminal tubules of distiphallus are often slender and elongated.

Immature stages
Finding distinct larval characters to identify Agromyza is not easy because the species exhibit mainly ancient characters.
Several species have some "filaments" (oral lobe) in central position between facial mask and mandibles (A frontella larva SEM.pct). They are not found in any other agromyzid genus but they are difficult to see without scanning electron microscope. The dorsal sclerites (fig.) present in many genera as vestigial structures, are in many Agromyza (and somewhat different in Tropicomyia species) well developed. Mandibles are normally equal or nearly equal in size and have in most cases two, but sometimes 3-5 mouthhooks each (A albipennis Larva SEM.pct). The two posterior spiracles have often three spiracular openings of equal size, often with spiracular processes (A albipennis Larva3 SEM.pct). They are frequently directed posteriorly (A albipennis Larva2 SEM.pct). Dorsal bridge of cephalopharyngeal skeleton is constantly present. Dorsal wing of cephalopharyngeal skeleton consists of two parts, of these the upper one is distinctly rounded and the lower one almost straight.

Beside a few gall formers, Agromyza are leaf miners. Most larvae form blotch mines or wide linear mines after reaching their third instar. Pupation occurs always outside of the mine, usually in the soil. However, in swamp areas puparia glued on their host plant surface can be observed frequently.

Host plants
Within this genus many groups of host plants occur but there are some distinct Agromyza subgroups feeding on Poaceae (or other Monocotyledoneae), Fabaceae and Rosaceae each.

Economic importance
The best-known species is Agromyza frontella that feeds on alfalfa and was introduced to North America. Although the species continues spreading, the amount of damage is still a matter of debate. A number of grass mining species can seriously infest cultivated cereals.