Phytobia carbonaria (Zetterstedt, 1848)
IMPORTANT CHARACTERS
Adults
Wing length: 4 - 4.5 mm. Frons hardly projecting above eye. Vein R1 thickening hardly visible. Squamae with long dark hair and a narrow dark margin. 3-4 strong dorsocentral bristles present on mesonotum. Humeri sometimes somewhat lightish at margins.
Female oviscape very long.
Male terminalia
Aedeagus with distinct shape. Basiphallus is very similar to that of Phytobia cerasiferae.
Immature stages
Lateral sclerites of mandibular complex large, about as large as mandibular complex itself. Intermediate sclerite and basal part fused, dorsally almost straight with hyaline structures above. Dorsal bridge invisible. Ventral arm of basal part of cephalopharyngeal skeleton very short.
Posterior part of puparium (not larva) can be longer than illustrated in Spencer, 1973.
In general the Phytobia larvae are extremely long and slender (up to 3 cm long and 0.5 cm broad) and rather strong mouth hooks with the right mandible being distinctly larger than the left one. Usually the posterior spiracles have three bulbs, which are of nearly equal size. The puparia are not as slender as the larvae but somewhat longer than those of other Agromyzidae. They have probably all prothoracic horns.
More details on the general morphology of the genus can be found in the chapter on the Genus Phytobia.
BIONOMICS
The larva mines near the cambium of twigs and stems. The eggs are deposited into smaller twigs and the emerging larvae mine towards the base of the tree. Depending on the size of the tree the fully grown larvae escape from the tree near the root or above. Pupation takes place in the soil, the puparia usually can be collected near the base of the stems, in hollowed stems or sometimes in birds' nests on the trees. The life histories of the Phytobia species are apparently rather uniform and treated in general under Genus Phytobia.
HOST PLANTS
Malus (apple), Crataegus (Hawthorn), possible Cydonia (quince) (Spencer, 1973).
DISTRIBUTION
Norway, Denmark, Germany, Great Britain, Austria, probably widespread in northern Europe.
ECONOMIC IMPORTANCE
Larval feeding causes the so-called pith flecks in the wood of the respective host trees (fig. Tschirnhaus), which can affect stability and reduce the aesthetical and commercial value of the wood. Sometimes it is also reported that the vigor of infested young trees can be reduced in nurseries.