Melanagromyza dolichostigma

Melanagromyza dolichostigma de Meijere, 1922

M. dolichostigma shows high similarities with several other related species (see below), reliable identification is not easy.
The oviposition mode (see the part "Bionomics", below) can be a valuable character.

Wing length: 1.8 - 2.2 mm. Spencer, 1973 mentioned the "unusual metallic reddish-purple coloration". However, this character is apparently not invariable.
Male terminalia
Highly similar to M. cordiophoeta Spencer, 1961 from Singapore. Both species could be synonyms (Spencer, 1976). There is also high similarity to M. cunctans (Meigen, 1830) from Europe and Melanagromyza sojae (Spencer, 1973).
Immature stages
The larvae lack the typical central horn of posterior spiracles, larval mandibles with one mouth hook each, the left one distinctly larger than the right one. Locomotion welts clearly consist of two types of denticles (Sasakawa, 1961). Two striking characters are the extremely elongated anterior and posterior spiracles. However, these features shares dolichostigma with the related but only poorly understood species Melanagromyza koizumii from Japan. Separation is possible only by the mode of female oviposition.

The behaviour and feeding pattern was described by van der Goot, 1930, Lee, 1976 and summarized by Talekar, 1990: The females show an unusual oviposition behaviour in that the eggs are not deposited in the leaf tissue but rather on the surface. Although the leaf surface is superficially punctured by the female ovipositor, the attachment of the eggs requires well developed leaf hairs (trichomes) on the underside, where the eggs are laid. Because these hairs are missing on cotyledons and unifoliate leaves, the species are not a threat for seedlings. Instead, they rather occur on about three to four weeks old plants. Although the eggs are not deposited in holes, the female ovipositor is not out of function. Sometimes the females make superficial cavities into the wrinkled leaves to attach the egg. As in other agromyzids, the females also make feeding punctures, which are mainly made on the upper side of the leaf. Generally young not fully unfolded leaves on the tip of the shoot are preferred for oviposition because the density of trichomes is higher. The hatched larva mines directly through a leaf vein and petiole into the stem.
Once in the stem, the larva feeds initially on the outer layers and, after feeding down the stem for 2-3 cm, starts to penetrate deeper into the stem. In this state normally the vascular tissue of the stem is affected by larval feeding.
However, descriptions of the nature of larval feeding differ: van der Goot, 1930 reported the larvae (usually more than one) finally feed concealed in the stem pith. According to Lee, 1976, after initially having mined downwards, the larva turns (usually only one in the same stem) and makes characteristic transverse coil shaped mines around the stem (good fig. not available). This feeding mode damages the plant particularly severe because the whole vascular tissue of the stem is affected.
The obvious inconsistencies in biological observations indicate the possible existence of cryptic species (see also Melanagromyza koizumii).
As usual for the taxonomic group Melanagromyza dolichostigma belongs to, pupariation takes place within the mine. The whole developmental time ranges from 17-21 days, the larval period alone requires 9-10 days.
The larval mining activity generally occurring at the apex of the plant causes destruction of vessels and can lead to wilting of young shoots. As a result, the growth is stunted. A plant infested by many larvae can develop gall-like thickenings.

The following fabacean plants are known to be consumed: Calopogonium mucunoides, Crotalaria juncea, Glycine max, Phaseolus spp., Puraria javanica, Vigna mungo, Vigna radiata, Vigna umbellata.
The main host appears to be soybean (Glycine max).

Indonesia, Japan, Taiwan, Thailand.

Although the damage individual larvae can cause is high, M. dolichostigma is regarded as not very dangerous because populations are normally smaller than those of other agromyzids on tropical legumes (Spencer, 1973). However, in mountain areas of Java and Taiwan the damage can be more significant (Lee, 1976, van der Goot, 1930). Talekar, 1990 reported that the damage of M. dolichostigma is greater after the flowering period of the host plant. In that stage the plants hardly can compensate for wilted shoots.