Cecidomyiidae

Rabdophaga

Salix humilis

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Rabdophaga saliciscornu

S. cornu

On S humilis

A lateral bud deformed into the shape of a monothalamous. very elongate, slender, cylindrical, tapering, hollow, rigid horn, very slightly pubescent, of a very dark reddish brown color when mature, and with about 12 or 14 longitudinal, pretty regular striae like a coleopterous elytrum. This gall is .30 — .77 inch long, .07 — .10 inch in diameter at base and .05 — .07 inch close to the tip. where for the length of about .10 inch it is flattened and moderately pubescent, and at the extreme tip, which is rounded, opens by a terminal slit. Sometimes it is solitary, sometimes 2 or 3 of them, or even as many as 10, grow at irregular intervals on a small twig 4 inches long, with a few of the intervening buds in their normal condition. Generally it is perfectly straight, diverging upwards from the twig at an angle of 15° — 35°, but occasionally it is a little bent in the middle, and occasionally it curves backwards in a regular curve, so that in one instance the tip nearly touches the base. When cut into, the walls of the hollow are seen to be no thicker than stout paper, but very stiff and hard, and on the terminal 1/2 the internal surface is pretty smooth with indistinct longitudinal rugae, except the terminal .05 inch, which is armed with very long, whitish pubescence directed obliquely forwards. In the basal 1/2 of the horn lies the cocoon, which is closely agglutinated to the walls of the cell except at its tip, where it forms a filmy, whitish diaphragm as in S. siliqua n. sp. ? The cell formed by the hollow of the de- formed bud is prolonged into the woody origin of the bud for .10 — .15 inch, but the twig itself is not swelled or deformed, as it is in the allied polythalamous gall S. triticoides n. sp., further than by a slight and scarcely noticeable intumescence at the origin of the bud. 

Described from 8 living specimens on four different twigs and 10 old dead and dry specimens all on one twig, the whole gathered in November. Out of the 18. 6 or 7 had been bored laterally by some minute parasite, and from at least two of the recent ones parasites had perhaps escaped at the terminal slit, for they contained neither larva nor cocoon, and were unbored, although one of the recent ones was bored. Rare near Rock Island, and difficult to discover from its simulating a short, lateral twig. When these galls occur in great numbers on a twig, the intervening buds perish, but when there are only one or two of them, they do not. When the twig is .08 inch or less in diameter, the part of it which lies beyond the galls shrivels up and perishes, even if there be only one of them, but when the diameter is .13 or over and there is but a single gall, it survives, at all events till the next season.

On the Insects, Coleopterous, Hymenopterous & Dipterous: Inhabiting the Galls of Certain Species of Willow. Pt 1st--Diptera

Rabdophaga saliciscornu

Host: Salix humilis

Salix
Bud gall not comprising imbricated, modified leaves
Complex gall; lateral bud deformed into elongate, thin-walled, hornlike structure

[A drawing of this gall appears on page 277, Figure 411]

Galls are monothalamous, 10-20 cm long, about 2 mm wide, pointed at the tip, and slightly curved.

Range: IL

The plant-feeding gall midges of North America

Rabdophaga cf. saliciscornu

[A photo of this gall appears on page 4 of the pdf]

At the outlet of Nordic Lake I found horn-like galls (Figure 5) on Salix pulchra Cham. (Malpighiales: Salicaceae) that were identical in form to those caused by Rabdophaga salicis-cornu (Osten Sacken, 1878) on Salix humilis Marshall in Illinois (Gagné, 1989) and by Rabdophaga repenticornua Bland, 2001 on Salix repens L. in Scotland (Bland, 2001). 

Collection data: USA: Alaska, Soldotna, outlet stream of Nordic Lake, 60.4444°N, 151.0818°W ± 200 m, 21.Dec.2016, ML Bowser, in horn-like bud gall on Salix pulchra (KNWR:Ento:11183, KNWR:Ento:11184). 

The closest match on BOLD for the single specimen I submitted was 88.23% similar. The sequence has not been assigned to a BIN

Notes on using LifeScanner for DNA-based identification of non-marine macroinvertebrates