The Arthropod Associates of 155 North American Cynipid Oak Galls

Abstract

The identities of most arthropod associates of cynipid-induced oak galls in the western Palearctic are generally known. However, a comprehensive accounting of associates has been performed for only a small number of the galls induced by the estimated 700 species of cynipid gall wasps in the Nearctic. This gap in knowledge stymies many potential studies of diversity, coevolution, and community ecology, for which oak gall systems are otherwise ideal models. We report rearing records of insects and other arthropods from more than 527,306 individual galls representing 201 different oak gall types collected from 32 oak tree species in North America. Of the 201 gall types collected, 155 produced one or more arthropods. A total of 151,075 arthropods were found in association with these 155 gall types, and of these 61,044 (40.4%) were gall wasps while 90,031 (59.6%) were other arthropods. We identified all arthropods to superfamily, family, or, where possible, to genus. We provide raw numbers and summaries of collections, alongside notes on natural history, ecology, and previously published associations for each taxon. For eight common gall-associated genera (Synergus, Ceroptres, Euceroptres, Ormyrus, Torymus, Eurytoma, Sycophila, and Euderus), we also connect rearing records to gall wasp phylogeny, geography, and ecology -including host tree and gall location (host organ), and their co-occurrence with other insect genera. Though the diversity of gall wasps and the large size of these communities is such that many Nearctic oak gall-associated insects still remain undescribed, this large collection and identification effort should facilitate the testing of new and varied ecological and evolutionary hypotheses in Nearctic oak galls.

Keywords: Cynipini; Diversity; Gall; Ormyrus; Synergus; Torymus.

Fig. 1.

Summary of data for Synergus inquilines reared from Nearctic galls. a) Associations of Synergus mapped to the Ward et al. (2022) Nearctic oak gall wasp phylogeny (Fig. S1). Numbers at tips of branches refer to those in figure S1. Closed circles at branch tips indicate Synergus was reared from galls of that gall wasp species in this study. Open circles indicate other previously known associations either not studied by us or not recovered in our collections. Blue-colored branches within the phylogeny indicate Palearctic gall wasps. b) Total number of gall types from which Synergus were reared in the three bioregions identified by Hipp et al. (2018) as constituting different assemblages of North American oaks: Californian (blue), Mexican and Central American (orange), and Eastern North American (green) floristic provinces. Numbers in parentheses indicate the total number of gall types collected in each region, excluding gall types from which no insects emerged. For figures c–f, gall types from which fewer than five individual insects were reared were excluded, whether or not a Synergus was reared. c) Associations of Synergus with trees in sections Quercus (Q), Lobatae (L), and Virentes (V). Gray bars and numbers indicate gall types with which a Synergus was associated. White bars and numbers indicate the number of gall types from which a Synergus was not reared. d) Association of Synergus with gall types on different oak tissues. Clockwise from top left: leaf, stem, acorn, flower, petiole, bud (“Bud” includes galls that may be found on both buds or stems. “Petiole” includes galls that may be found on both petioles and stems or petioles and leaves); e) proportion of gall types of three size categories (“small” < 0.5 mm; “medium”, “large” > 20 mm) from which Synergus were reared. f) Results of probabilistic co-occurrence analysis (Veech 2013) for Synergus against seven other common associates (Cer = Ceroptres, Euc = Euceroptres, Orm = Ormyrus, Syc = Sycophila, Tor = Torymus, Eur = Eurytoma, Eud = Euderus). Yellow = significantly less likely to co-occur; blue = significantly more likely to co-occur; gray = no difference from probabilistic expectations. g) Synergus lateral habitus.

Fig. 2.

Summary of data for Ceroptres inquilines collected from Nearctic galls. For full explanation of figure details, refer to figure 1 legend. a) Associations of Ceroptres with the Nearctic oak gall wasp phylogeny (Fig. S1). b) Gall types from which Ceroptres were reared in the Californian (blue), Mexican and Central American (orange), and Eastern North American (green) floristic provinces. c) Associations of Ceroptres with trees in sections Quercus (Q), Lobatae (L), and Virentes (V). d) Association of Ceroptres with gall types on different oak tissues. e) Proportion of gall types of three size categories (“small” < 0.5 mm; “medium”, “large” > 20 mm) from which Ceroptres were reared. f) Results of probabilistic co-occurrence analysis for Ceroptres against seven other common associates. Yellow = significantly less likely to co-occur; blue = significantly more likely to co-occur; gray = no difference from probabilistic expectations. g) Ceroptres lateral habitus.

Fig. 3.

Summary of data for Euceroptres inquilines collected from Nearctic galls. For full explanation of figure details, refer to figure 1 legend. a) Associations of Euceroptres with the Nearctic oak gall wasp phylogeny (Fig. S1). b) Gall types from which Euceroptres were reared in the Californian (blue), Mexican and Central American (orange), and Eastern North American (green) floristic provinces. c) Associations of Euceroptres with trees in sections Quercus (Q), Lobatae (L), and Virentes (V). d) Association of Euceroptres with gall types on different oak tissues. e) proportion of gall types of three size categories (“small” < 0.5 mm; “medium”, “large” > 20 mm) from which Euceroptres were reared. f) Results of probabilistic co-occurrence analysis for Euceroptres against seven other common associates. Yellow = significantly less likely to co-occur; blue = significantly more likely to co-occur; gray = no difference from probabilistic expectations. g) Euceroptres lateral habitus.

Fig. 4.

Summary of data for Ormyrus collected from Nearctic galls. For full explanation of figure details, refer to figure 1 legend. a) Associations of Ormyrus with the Nearctic oak gall wasp phylogeny (Fig. S1). b) Gall types from which Ormyrus were reared in the Californian (blue), Mexican and Central American (orange), and Eastern North American (green) floristic provinces. c) Associations of Ormyrus with trees in sections Quercus (Q), Lobatae (L), and Virentes (V). d) Association of Ormyrus with gall types on different oak tissues. e) proportion of gall types of three size categories (“small” < 0.5 mm; “medium”, “large” > 20 mm) from which Ormyrus were reared. f) Results of probabilistic co-occurrence analysis for Ormyrus against seven other common associates. Yellow = significantly less likely to co-occur; blue = significantly more likely to co-occur; gray = no difference from probabilistic expectations. g) Ormyrus lateral habitus.

Fig. 5.

Summary of data for Torymus collected from Nearctic galls. For full explanation of figure details, refer to figure 1 legend. a) Associations of Torymus with the Nearctic oak gall wasp phylogeny (Fig. S1). b) Gall types from which Torymus were reared in the Californian (blue), Mexican and Central American (orange), and Eastern North American (green) floristic provinces. c) Associations of Torymus with trees in sections Quercus (Q), Lobatae (L), and Virentes (V). d) Association of Torymus with gall types on different oak tissues. e) proportion of gall types of three size categories (“small” < 0.5 mm; “medium”, “large” > 20 mm) from which Torymus were reared. f) Results of probabilistic co-occurrence analysis for Torymus against seven other common associates. Yellow = significantly less likely to co-occur; blue = significantly more likely to co-occur; gray = no difference from probabilistic expectations. g) Torymus lateral habitus.

Fig. 6.

Summary of data for Sycophila collected from Nearctic galls. For full explanation of figure details, refer to figure 1 legend. a) Associations of Sycophila with the Nearctic oak gall wasp phylogeny (Fig. S1). b) Gall types from which Sycophila were reared in the Californian (blue), Mexican and Central American (orange), and Eastern North American (green) floristic provinces. c) Associations of Sycophila with trees in sections Quercus (Q), Lobatae (L), and Virentes (V). d) Association of Sycophila with gall types on different oak tissues. e) proportion of gall types of three size categories (“small” < 0.5 mm; “medium”, “large” > 20 mm) from which Sycophila were reared. f) Results of probabilistic co-occurrence analysis for Sycophila against seven other common associates. Yellow = significantly less likely to co-occur; blue = significantly more likely to co-occur; gray = no difference from probabilistic expectations. g) Sycophila lateral habitus.

Fig. 7.

Summary of data for Eurytoma collected from Nearctic galls. For full explanation of figure details, refer to figure 1 legend. a) Associations of Eurytoma with the Nearctic oak gall wasp phylogeny (Fig. S1). b) Gall types from which Eurytoma were reared in the Californian (blue), Mexican and Central American (orange), and Eastern North American (green) floristic provinces. c) Associations of Eurytoma with trees in sections Quercus (Q), Lobatae (L), and Virentes (V). d) Association of Eurytoma with gall types on different oak tissues. e) proportion of gall types of three size categories (“small” < 0.5 mm; “medium”, “large” > 20 mm) from which Eurytoma were reared. f) Results of probabilistic co-occurrence analysis for Eurytoma against seven other common associates. Yellow = significantly less likely to co-occur; blue = significantly more likely to co-occur; gray = no difference from probabilistic expectations. g) Eurytoma lateral habitus.

Fig. 8.

Summary of data for Euderus collected from Nearctic galls. For full explanation of figure details, refer to figure 1 legend. a) Associations of Euderus with the Nearctic oak gall wasp phylogeny (Fig. S1). “s” = Euderus set, “c” = Euderus crawfordi, “n” = possible new Euderus species. * = this association with a Palearctic oak tree is only known from trees introduced to California. ** = the approximate phylogenetic location of this host of E. crawfordi (see text). b) Gall types from which Euderus were reared in the Californian (blue), Mexican and Central American (orange), and Eastern North American (green) floristic provinces. c) Associations of Euderus with trees in sections Quercus (Q), Lobatae (L), and Virentes (V). d) Association of Euderus with gall types on different oak tissues. e) proportion of gall types of three size categories (“small” < 0.5 mm; “medium”, “large” > 20 mm) from which Euderus were reared. f) Results of probabilistic co-occurrence analysis for Euderus against seven other common associates. Yellow = significantly less likely to co-occur; blue = significantly more likely to co-occur; gray = no difference from probabilistic expectations. g) Euderus lateral habitus.