Agromyza megalopsis Hering, 1933
IMPORTANT CHARACTERS
Adults
Wing length: about 2.5 - 2.7 mm. Body fine pubescent and shining, mesonotum green metallic.
4-5 Dorsocentral bristles present, of these 1-2 can be presutural. The first, presutural dc are about half as long as the hind ones.
Immature stages
Posterior spiracles of larva and puparium with each three bulbs. The position of the two spiracles can be used to separate megalopsis from the closely related Agromyza nigrella: In megalopsis the two posterior spiracles are situated close together (Ag megalopsis post sp Sp.pct) whereas those of nigrella are more separated (Ag nigrella post sp Sp.pct) (Spencer, 1973).
BIONOMICS
Young larvae form narrow linear mines, the full grown larvae cause large blotches of full depth mines. Frequently several larvae can be found in the same mine. The affected leaves are often wilting or even dying.
The bionomics has been studied by GeigenmÜller, 1966, Scherney, 1966, Weigand, 1966 and Scherney and Weigand, 1967. The authors of the latter three citations referred to Agromyza nigrella instead of megalopsis. But some figures indicate that the species most probably was confused with megalopsis (Spencer, 1973).
According to the authors of the papers mentioned above, in Germany oviposition occurs mainly in June and the females can lay from 20-30 eggs. Usually the pupariation occurs in the soil but occasionally puparia can be found in the mines. Most of the early summer generation of larvae fall in diapause and hibernate as pupa but a part of the population emerge in the late summer or autumn. Hering, 1962 reported that the species pupates within the leaf, which is unusual within the genus Agromyza. However, it is not clear if it is the regular behaviour.
HOST PLANTS
Cereals: Hordeum vulgare, Hordeum distichon (barley), possibly also Secale cereale L. (rye). Most probably many wild grasses are also used as host plant.
DISTRIBUTION
Records exist from Germany, the former Czechoslovakia, Hungary, France, Iraq. Most probably the species is widespread among the palaearctic region.
ECONOMIC IMPORTANCE
In Europe megalopsis is one of the important Agromyza species frequently occurring on cereals. The first and probably heaviest outbreaks were observed in 1964 and 1965 in Southern Germany (Spencer, 1973). Together with other species or alone Agromyza megalopsis can cause damage on the leaves of cereals. D'Aguilar et al., 1976 who investigated megalopsis together with Agromyza nigrella, Agromyza intermittens and Agromyza luteitarsis concluded that megalopsis were the most damaging species. However, despite the leaf damage, significant grain yield reduction cannot always be detected.