Bassettia flavipes (Gillette, 1889), comb. nov., asexual generation

[Synonyms listed for the sexual generation]

Material examined: Fifteen females “Canada, Alberta, University of Alberta, Edmonton, leg. S. Digweed, 27/04/2007, Q. macrocarpa”

Gall. Asexual galls (Fig. 93) are inconspicuous stem galls comprised of individual larval cells within corky bark on 2–3 year old twigs of Q. macrocarpa. Galls are not evident as swellings on twig surfaces. Galls are not induced on twigs of the previous year’s growth, nor are they present in smooth twigs.

Biology. Asexual females of B. flavipes emerged in mid- to late April in Edmonton and oviposited into swelling buds, preferring those having the bud scales slightly open with green showing between them. Females actively palpated prospective buds, and briefly probed them by inserting their ovipositors between bud scales. Females then quickly plunged their ovipositors fully into the bud, oviposited for 10-20 seconds, retracted their ovipositors, and departed. Females mostly seemed to avoid buds into which they or other females had previously oviposited.

Sexual generation galls have been recorded from Q. macrocarpa and Q. alba (Burks 1979, Weld 1926), and the authors additionally observed them on Q. ⨯ bebbiana (Q. alba x Q. macrocarpa) and Q. ⨯ schuettei (Q. bicolor x Q. macrocarpa) at the Jardin Botanique de Montreal in August 2007.

Distribution. USA: Illinois, Indiana, Iowa, Minnesota, North Dakota, Virginia; Canada: Alberta, Ontario (Weld 1926, Burks 1979, Ives & Wong 1988, Bergdahl 2015). Within Canada, the authors have observed galls of the sexual generation on introduced bur oaks in Alberta, and on bur oaks within their native range in Manitoba and Quebec.

Comments. Suspected galls of the asexual generation of B. flavipes have been identified as a source of damage on ornamental bur oaks because, at high population levels, they may attract birds which damage twigs while extracting larvae from galls (Ives & Wong 1988; Bergdahl 2015). Photos of this damage suggest that galls containing larvae may occur on a greater variety of stem sizes and maturities than we observed, perhaps as a function of higher population densities. It is also possible that old galls bearing exit holes, which persist on larger and older stems, house other insects that are sought by birds.

Rearings of asexual galls of B. flavipes from Edmonton, Alberta produced multiple other gall occupants. The most common (88%) alternative occupant was a species of Ceroptres Hartig, 1840; this genus is an inquiline in cynipid galls, although it is not clear if it is lethal to the original gall inducer (Ronquist et al. 2015). It appeared to specialize on B. flavipes in Edmonton, as it was not reared from other bur-oak-galling cynipids there (S. Digweed, unpublished data). We also reared the chalcid parasitoids Ormyrus labotus Walker, 1843, and Sycophila marylandica (Girault, 1916), from asexual galls. All parasitoids emerged from mid-May to mid-June. We also reared these three species from sexual galls of B. flavipes, as well as adults of the parasitoids Baryscapus racemariae (Ashmead, 1886), Sycophila dubia (Walsh, 1870), and Eurytoma studiosa Say, 1836. These alternative occupants of sexual B. flavipes galls emerged between early July and mid-August. Sycophila foliatae (Ashmead, 1881), S. quercilanae (Fitch, 1859), and S. xanthochroa (Ashmead, 1894), have been reared elsewhere from sexual galls of B. flavipes (Noyes 2016).

- James Nicholls, George Melika, Scott Digweed, Graham Stone: (2022) Pairing of sexual and asexual generations of Nearctic oak gallwasps, with new synonyms and new species names (Hymenoptera: Cynipidae, Cynipini)^©