Rhabdophaga strobiloides Walsh.

Host Salix cordata Muhl. [eriocephala]

"The galls are very uniform in size and form, usually top-shaped, some inclining to spherical, a little oblate below and prolate above, and as the female oviposits but one egg in the terminal bud of the willow shoot, the galls are terminal and monothalamous. "The gall is a rather tightly and regularly arranged mass of from 70 to 80 aborted leaves, representing perhaps about i m. of the leafage of a normal branch. "The average measurement of 200 galls was 12 mm. X15 mm., and the length of the deformed part of the branch included in the gall around which the aborted leaves were packed was 6 mm." — Brodie.

The leaves that constitute the principal mass of this gall do not take any part in supplying the larva with food. The tissue that has this function is composed of a mass of small, thin-walled cells. It terminates the stem axis and the larva is in immediate contact with it (Fig. 24). This tissue which really furnishes a nutritive layer seems to originate from a cambium-like tissue at the base of the mass of cells. An important factor in the production of this gall is the practical cessation of growth of the bud axis. The aborted leaves that compose the gall exhibit very slight anatomical aberrations.

Cecidomyia strobiloides

Rhabdophaga strobiloides

C. strobiliscus. Willow species. C. strobiloides Mass., N. H. June- July. Pine cone forms on stem.

[Bowser et al sequence the genomes of R strobiloides specimens reared on Salix hookeriana, barclayi, commutata, sitchensis, richardsonii, and bebbiana in Alaska and on Salix nigra in Michigan. They find that these samples are monophyletic with respect to other Rabdophaga specimens they sequenced and conclude the Alaskan midges are Rabdophaga cf strobiloides and may be conspecific with R strobiloides. They note that previous studies have listed R strobiloides on Salix cordata, eriocephala, humilis, nigra, and scouleriana.]

Morphologically, all galls of Alaskan Rabdophaga that we collected were more open than what is typical of R. strobiloides. In the key of Gagné (1989) they would have been identified as R. salicisbrassicoides, R. salicisrhodoides, or Rabdophaga saliciscoryloides, which form more open rosette galls. Most Alaskan rosette galls more closely resemble illustrations and photographs of European R. rosaria than any of these North American species. An exception is the unusual morphology of rosette galls on S. sitchensis, which often contain more than one midge larva and which often have new stems originating from leaf axils within the galls.

[Sato et al sequenced the genomes of Rabdophaga strobiloides from Salix sitchensis and barclayi in Alaska and Salix nigra in Michigan and found they were monophyletic.]

Rhabdophaga strobiloides

Cecidomyia strobiloides
Cecidomyia salicis-strobiloides

Hosts: Salix longifolia [interior]

Terminal bud-gall, showing as a rounded conical mass of closely appressed scale-like leaves. Green, with a whitish silky covering. 2.5-3 x 4 cm. Usually abundant, but scarce this year.

Rhabdophaga strobiloides

Cecidomyia strobiloides
Cecidomyia salicis-strobiloides

Cone-shaped gall consisting of a deformed terminal bud, the leaves closely overlapping. Monothalamous. 2-3 cm. long. Very abundant on willows. Fully grown in July. Insect emerges the following spring. On several species of willows, Salix.

Rhabdophaga strobiloides

Pine conelike gall, length 2 to 2.5 cm