Three new records of gall inducers in Alaska
by Ramsey Sullivan1
Introduction
Galls are growths made of plant tissue and induced by another organism. The inducer lives some or most of its lifecycle within the gall. Galls provide shelter and food for the inducer, often at the expense of the host.
Most galls are induced by arthropods, although bacteria, fungi, plants, and other organisms are known to induce them as well. Gall midges and gall wasps, Cecidomyiidae and Cynipidae, encompass the two largest groups of arthropod gall inducers with over 800 and 700 gall inducing species known to occur in North America, respectively (Russo 2021, Gagné and Jaschhof 2025).
Preliminary descriptions and distributions for two gall midges and one gall wasp previously unrecorded in Alaska are provided in the following section organized by associated plant hosts.
Gall Descriptions by Host
Arctostaphylos uva-ursi (L.) Spreng.
Figure 1: From left to right: Galls observed near Lake Louise State Recreation Area (Aug. 2023); Dissection of the previous gall showing a Cecidomyiid larva of unknown species; Terminal and lateral galls observed on Horseshoe Lake Trail, Denali National Park and Preserve (Aug. 2023); Dissected gall after snowmelt showing a cecidomyiid larva, Lake Louise State Recreation Area (May 2025).
Description
An unknown gall midge (Cecidomyiidae) induces single chambered rosette galls on the lateral and terminal buds of kinnikinnick or bearberry, Arctostaphylos uva-ursi (Figure 1). Galls rarely contain multiple larvae. Orange larvae overwinter in the galls and emerge the following spring. Galls halt development of terminal and lateral shoots. A single partially emerged adult was reared from galls collected on May 17th, 2025, and found deceased June 8th, 2025. Additional rearing attempts will be made in Spring 2026.
A Gallformers.org code, “a-uva-ursi-bud-gall”2, has been made to track observations of this midge on the community science platform, iNaturalist.org. No record of a midge-induced bud gall on Arctostaphylos uva-ursi could be found in reviewed literature (Felt 1928, Gagné 1989, Skuhravá and Skuhravý 2021, Redfern et al. 2023, Gagné and Jaschhof 2025, Ellis 2026, UAM 2026).
Distribution
Uncommon occurrences have been noted by the author in Interior and Southcentral Alaska to British Columbia.
Picea glauca (Moench) Voss & Picea mariana (Mill.) Britton, Sterns & Poggenb.
Figure 2: From left to right: Gall at the base of the previous year’s shoot with shoot basal scales removed, host: Picea mariana (May 2024); Gall midge exuvia outside a gall on a shoot with basal scales removed, host: Picea mariana (June 2024); Pupa dissected from a gall with strongly sclerotized serrated fused antennal horns, host: Picea mariana (reared indoors for one month, January 2024); Adult female post emergence, host: Picea mariana (June 2024).
Description
An undetermined gall midge (Cecidomyiidae) induces enlarged bud galls at the base of new shoots on black spruce, Picea mariana, and white spruce, Picea glauca (Figure 2). It is not known if it utilizes other Picea species. Orange larvae overwinter in galls and pupate and emerge the following spring. Larvae were observed in the dissected galls of P. mariana from Port Alsworth, AK on May 23, 2024, pupae on June 9th, 2024, with adults emerging from collected galls on June 11th, 2024. Pupae exhibit strongly sclerotized serrated fused antennal horns that likely assist in exiting the gall. Host damage is not superficially apparent; galled buds are often covered by the remnant scales of the bud from which the affected shoot developed.
A Gallformers.org code, “p-mariana-bud-scale-gall”3, has been made to track observations of this midge on the community science platform, iNaturalist.org. No record of a midge-induced bud gall at the base of shoots of Picea spp. could be found in reviewed literature. (Gagné 1989, Fedotova and Averenskij 2016, Skuhravá and Skuhravý 2021, Redfern et al. 2023, Gagné and Jaschhof 2025, Ellis 2026, UAM 2026).
Distribution
Common in Matanuska-Susitna and Lake and Peninsula Boroughs, though presence throughout host ranges is unknown.
Potentilla norvegica L.
Figure 3: From left to right: Diastrophus tumefactus stem gall on Potentilla norvegica, Fairbanks (July 2025); Same plant as previous after nearly 6 weeks, Fairbanks (August 2025); Dissected D. tumefactus gall, Fairbanks (July 2025); Wasp larva in early season gall, Palmer (July 2025).
Description
The rough cinquefoil gall wasp, Diastrophus tumefactus Kinsey 1920, was observed in Matanuska-Susitna and Fairbanks North Star Boroughs in July 2025 (Figure 3). D. tumefactus induces polythalamous or agglomerate stem swellings on Norwegian or rough cinquefoil, Potentilla norvegica. Galls were collected from Palmer and Fairbanks in August 2025 and sent to Charles Davis, a Ph.D. candidate at Penn State University studying the biodiversity and natural history of gall wasps utilizing hosts within Rosaceae, for rearing and incorporating into his ongoing research.
Distribution
These occurrences represent the northernmost detection of D. tumefactus. “Research grade” identifications on iNaturalist ranging south to Pennsylvania and east to Nova Scotia suggest that it could occur more broadly throughout the host range. The only previously published records of D. tumefactus were from Ontario and Quebec from samples collected in the late 1800s (Kinsey 1920, Nastasi and Deans 2021, Nastasi and Davis 2022, Bennett et al. 2024).
References
Gallformers.org Administrator, Chugiak, Alaska, ramzsullivan@protonmail.com↩︎