Phytobia setosa (Loew, 1869)
IMPORTANT CHARACTERS
Adults
Wing length: about 4.5 mm. Frons mat or at most slightly projecting above eye in profile, sooty black but normally at least faintly reddish adjoining lunule. Four frontorbital bristles present, sometimes a fifth one on one side or both. Of these normally the two frontal ones are inwards directed.
Frontorbital setulae are extremely tiny. Head laterally completely dark, lunule yellow, contrasting to the black frons. The surface of lunule is covered with fine silvery or whitish pubescence. Frons is normally faintly reddish adjoining lunule, otherwise black. Third antennal segment reddish brown.
Humeri dark, mesonotum pubescent, gray, with 3+1 strong dorsocentral bristles, scutellum dark, the two prescutellar bristles are remarkably strong. Legs largely black, knees only slightly paler. Costa extending to M 1+2.
Male terminalia
Distiphallus with long and thin terminal tubules, hardly diverging.
Immature stages
Larval diagnostic characters to distinguish between different Phytobia spp. are not yet exactly known. In general the 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 prothoracic horns. More detailed information can be found under 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 it. 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 are generally described in the chapter on the Genus Phytobia.
HOST PLANTS
Acer rubrum (Spencer and Steyskal, 1986), Acer saccharum (Wallner and Gregory, 1980), probably also some other Acer species.
DISTRIBUTION
Northern part of USA, Canada.
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 (see Genus Phytobia).