Bassettia flavipes ( Gillette, 1889 ) Nicholls & Melika & Digweed & Stone, 2022

Nicholls, James A., Melika, George, Digweed, Scott C. & Stone, Graham N., 2022, Pairing of sexual and asexual generations of Nearctic oak gallwasps, with new synonyms and new species names (Hymenoptera: Cynipidae, Cynipini), Zootaxa 5145 (1), pp. 1-79 : 28-34

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

Figs 82–93

Synonyms: Neuroterus flavipes Gillette 1889: 281 . Male, female and gall. Description reprinted by Gillette (1890: 21). Beutenmüller (1910: 136) suggested that this species should probably be placed in Callirhytis or Andricus rather than Neuroterus . Kinsey (1923: 136) agreed, and left this species unplaced in his revision of Neuroterus . Callirhytis flavipes (Gillette) : combination by Weld (1926: 91). Melika & Abrahamson (2002: 168) considered this species should belong to Andricus , however, this transfer was made only informally, without following the ICZN requirements.

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

Diagnosis. This species possesses the diagnostic characters of Bassettia Ashmead, 1887 : absence of a malar sulcus; the transversely rugose mesoscutum, dorsoventrally compressed mesosoma not arched in lateral view like in most Cynipini ; subparallel lateral propodeal carinae; and a ring of dense white setae basally on 2nd metasomal tergum ( Melika & Abrahamson 2007; Medianero & Nieves-Aldrey 2010). Bassettia flavipes also forms inconspicuous twig galls in the asexual generation and integral leaf galls in the sexual generation, as in other Bassettia species ( Melika & Abrahamson 2007; Medianero & Nieves-Aldrey 2010).

Bassettia flavipes most closely resembles B. tenuana Weld, 1921 . In B. flavipes the body is dark brown, the eye 2.0× as high as the length of the malar space, the notaulus incomplete, traceable at most along half the length of the mesoscutum, the forewing veins are light to transparent, the central propodeal area with numerous irregular short rugae, the metasoma as long as head+mesosoma and nearly as long as high in lateral view, 2nd metasomal tergum extending to 1/3 of metasoma length in dorsal view. In B. tenuana the body is black, the eye equal in height to the length of malar space, the notaulus complete, the forewing veins dark brown, the central propodeal area reticulate, the metasoma longer than head+mesosoma and distinctly longer than high in lateral view, 2nd metasomal tergum extending to 2/3 of metasoma length in dorsal view. Bassettia flavipes is also similar to B. gemmae Ashmead, 1896 ; both species have been recorded from Q. alba ( Weld 1926) . In B. flavipes the head and body dark brown, the mesoscutum uniformly alutaceous, the prominent part of the ventral spine of hypopygium more than 2.0× as long as broad in ventral view. In B. gemmae the head and body black, the mesoscutum transversely dull rugose, the prominent part of the ventral spine of hypopygium over 4.0× as long as broad in ventral view. In addition, the length-to-width ratio of the radial cell of B. gemmae is greater than that of B. flavipes . It must be also mentioned that the asexual and sexual females within Bassettia are very similar and only a few characters differentiate them.

Description. Asexual female ( Figs 82–92 ) Head, mesosoma, metasoma black; mouthparts, lower genal and clypeal margins, antennae, tegulae, coxal tips, bases and tips of femora and tibiae, tarsi apices, and ventral spine of hypopygium, all dark to light brown. Wing venation pale yellow or colourless.

Head alutaceous without setae; rounded, 1.3× as broad as high and as broad as mesosoma in frontal view, 2.2× as broad as long in dorsal view. Gena alutaceous, broadened behind eye in frontal view, as broad as transverse diameter of eye in lateral view. Malar space alutaceous, with very delicate, indistinct striae radiating from clypeus and reaching eye, eye 2.0× as high as height of malar space. Eyes slightly converging ventrally. POL 1.9× as long as OOL; OOL 2.0× as long as diameter of lateral ocellus and as long as LOL; lateral ocelli rounded, median ocellus ovate. Transfacial distance 1.3× as long as height of eye; diameter of antennal torulus 2.0× as long as distance between them, distance between torulus and eye as great as diameter of torulus. Antennal toruli level with the lower half of eye. Lower face alutaceous, with sparse short white setae, as high as frons, with short delicate striae radiating from clypeus and reaching eye, striae only alongside median part of lower face; sculpture of lower face rougher than frons; median area alutaceous, not elevated; lower face with two impressed smooth glabrous sulci starting from lateral edges of clypeus and extending to 1/3 of lower face height. Clypeus rectangular, 1.6× as high as broad, uniformly alutaceous, ventrally rounded, emarginate, without median incision, reaches beyond ventral edge of lower face; anterior tentorial pit small, rounded, inconspicuous; smooth, glabrous epistomal sulcus and smooth, glabrous clypeo-pleurostomal line distinct, strongly impressed. Frons and interocellar area uniformly alutaceous, without setae. Vertex, occiput, postocciput, postgena uniformly alutaceous, without parallel striae, with white setae; posterior tentorial pit large, ovate, area below impressed; occipital foramen slightly higher than height of postgenal bridge; hypostomal carina emarginate, continuing into united postgenal sulci which diverge toward occipital foramen, postgenal bridge anteriorly broader than high. Antenna longer than head+ mesosoma; with 12 flagellomeres (suture between F12 and F11 indistinct), scape and pedicel 2.0× as broad as F1, scape and pedicel shorter than F1, F1 1.4× as long as pedicel and 1.4× as long as F2, F2 longer than F3, F3=F4, F5=F6 and shorter than previous one, F7 to F11 nearly equal in length, F11 longer than F10; placodeal sensilla on F3–F12.

Mesosoma slightly longer than high. Pronotum alutaceous, with white setae along margin, laterally broader than width of mesopleuron, anterolateral edge impressed, smooth, without sculpture. Propleuron alutaceous, with sparse setae. Mesoscutum uniformly alutaceous; slightly longer than broad (greatest width measured across mesoscutum level with base of tegulae). Notaulus incomplete, very weakly impressed, traceable at most to half the length of mesoscutum; anterior parallel line and median mesoscutal sulcus absent; parapsidal line in the form of a smooth stripe, extending slightly above tegula; circumscutellar carina broad, smooth along tegula. Mesoscutellum ovate, slightly longer than broad; posteriorly rounded and emarginate; uniformly rugoso-reticulate, overhanging metanotum. Mesoscutellum with narrow short transverse semilunar impression anteriorly, with smooth, glabrous bottom, with central broad triangular elevated area. Mesopleuron with delicate transverse striae starting posteroventrally and extending across mesopleuron and widening towards anterodorsal end, anteroventral quarter of mesopleuron smooth, shiny; speculum shiny, with very delicate, hardly traceable striae; mesopleural triangle rugose, with white setae; dorsal and lateral axillar areas alutaceous, without setae; subaxillular bar smooth, glabrous, at posterior end as high as height of metanotal trough; metapleural sulcus reaching mesopleuron at half its height, delimiting smooth, shiny triangular area along mesopleuron; upper part of mesopleural sulcus indistinct. Metascutellum rugose, as high as height of smooth, glabrous ventral impressed area; metanotal trough alutaceous, glabrous, without setae; propodeum uniformly alutaceous, lateral propodeal carinae strong, slightly bent outwards in posterior 1/3 of propodeum height, delimiting smooth, shiny central propodeal area with numerous irregular short rugae; lateral propodeal area smooth, shiny with dense white setae. Nucha very short, with a few logitudinal sulci laterally and dorsally. Tarsal claws simple, without basal lobe.

Forewing longer than body, hyaline, with long dense cilia on margin, veins indistinct, pale, radial cell open, 4.2× as long as broad; R1 and Rs nearly reaching wing margin; areolet and Rs+M indistinct.

Metasoma as long as head+mesosoma, nearly as long as high in lateral view; 2nd metasomal tergum extending to 1/3 of metasoma length in dorsal view, with dense white setae anterolaterally; all terga smooth, glabrous, without micropunctures. Hypopygium without micropunctures, prominent part of ventral spine of hypopygium 2.1× as long as broad in ventral view, with a few short setae ventrally. Body length 1.4–2.1 mm long (n = 15).

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 are multilocular, fleshy swellings along the leaf midrib or major lateral veins ( Fig. 94 ) and are visible starting in mid- to late May in Edmonton. Adults emerged starting in late June or early July, and males tended to begin emerging earlier than females. Each emerging adult appeared to cut its own exit hole from the gall. Adult females of the sexual generation of B. flavipes oviposited into twig bark. We did not assess whether unmated females oviposited or produced viable eggs. 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.

Molecular taxonomy. This species was first described from adults of the sexual generation and galls on Q. macrocarpa ( Gillette 1889) ; Ives & Wong (1988) tentatively identified adults and galls of the asexual generation of B. flavipes but did not provide any confirmatory evidence. Herein, alternating generations are matched for the first time using DNA data, with four individuals (two asexual females, two sexual females) sequenced for both cytb and ITS2. Cytb sequences were on average 0.54% divergent (range 0–0.92%; GenBank accessions MN184628 – MN184631 ). Six ITS2 sequences were observed across the four individuals (two individuals being heterozygous; MN184632 – MN184637 ); those sequences were 0–0.60% divergent with three indels observed across all sequences.

The B. flavipes cytb haplotypes were on average 8.24% divergent from the only other published Bassettia cytb sequence, obtained from B. pallida (GenBank accession MG821072 ; Nicholls et al. 2018b). In addition, ITS2 sequences among the two species were about 6.64% different, with 21 indels (GenBank accession OM331820 for B. pallida ). These divergences are consistent with those expected for congeneric species, confirming our generic-level re-classification of this species.

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) .

Figures

FIGURES 82–87. Bassettia flavipes (Gillette), asexual generation, female. 82–85, head: 82, frontal view, 83, dorsal view, 84, posterior view, 85, lateral view. 86, antenna. 87, pronotum and propleuron, frontal view.

FIGURES 88–91. Bassettia flavipes (Gillette), asexual generation, female. 88, mesosoma, lateral view, 89–90, mesoscutum and mesoscutellum, dorsal view, 91, metascutellum and propodeum, posterodorsal view.

FIGURES 92–94. Bassettia flavipes (Gillette). 92, asexual generation, female, metasoma, lateral view. 93, asexual gall. 94, sexual gall.