Hymenoptera

Ward, Anna K. G., Busbee, Robert W., Chen, Rachel A., Davis, Charles K., Driscoe, Amanda L., Egan, Scott P., Goldberg, Bailey A. R., Hood, Glen Ray, Jones, Dylan G., Kranz, Adam J., Meadely-Dunphy, Shannon A., Milks, Alyson K., Ott, James R., Prior, Kirsten M., Sheikh, Sofia I., Shzu, Shih-An, Weinersmith, Kelly L., Zhang, Linyi, Zhang, Y. Miles & Forbes, Andrew A., 2022, Borneosa aspera, Zoological Studies 61 (57), pp. 1-30 : 12

( Hymenoptera : Chalcidoidea: Ormyridae )

4,658 individuals (mean = 67.5, range 1–2,175) reared from 69 gall types ( Table S1).

Summary of Natural History: In comparison to other genera of parasitoids associated with oak galls, wasps in the genus Ormyrus have been described as generally more restricted to galls on oaks. For example, Torymus and Eurytoma both have oak gall associated species but attack many other hosts as well. All but two of the known Nearctic Ormyrus species attack galls on oaks-the exceptions attack Cynipid gall wasps on roses and Pteromalid gall inducers on blueberries ( Hanson 1992). Though 16 species were described in the most recent revision of Nearctic Ormyrus ( Hanson 1992) , more recent genetic and ecological data suggest that these wasps are considerably more species rich and ecologically specialized than previously supposed ( Sheikh et al. 2022).

Ormyrus larvae are generally known as ectoparasites, and in the Palearctic have been shown to directly parasitize the larvae of gall forming wasps, though it is also possible that they can attack inquilines and other parasitoids in the same galls ( Redfern and Askew 1998) or that they are inquilines themselves. Indeed, observations in the context of biocontrol suggest that Ormyrus can act as hyperparasitoids of Torymus wasps ( Cooper and Rieske 2011). Moreover, experiments tracking insects emerging from individual Belocnonema leaf galls that are unilocular (or contain only one gall wasp larvae) show that Ormyrus wasps can emerge from the same individual gall as other adult gall associates, including Synergus , Sycophila , and Brasema Cameron ( Hall 2001) . Multiple individual Ormyrus were also observed emerging from the same individual gall ( Hall 2001), which suggests that they were acting as inquilines or attacking insects other than the gall former.

Relationship to galler phylogeny: Ormyrus were reared in this study or previously reared by others from almost all gall types included in the Nearctic gall wasp phylogeny ( Ward et al. 2022) phylogeny, including from all four Palearctic clades ( Fig. 4a ). Members of the genus are near ubiquitous in associations with oak gall wasps.

Biogeography and oak tree section: Ormyrus were reared from galls collected in all three floristic regions of North America ( Fig. 4b ) and from 40% or more of gall types monitored in each of the three oak tree sections surveyed ( Fig. 4c ).

Tree organ and gall size: Ormyrus were associated with galls on all tree organs represented in our collections ( Fig. 4d ) and from galls of all sizes, with a slight bias towards larger galls ( Fig. 4e ). Previous rearing records also show that Ormyrus can use root galls produced by cynipids ( Hanson 1992).

Co-occurrence with other natural enemies: We found only one significant correlation between Ormyrus and another insect genus: a positive correlation with Eurytoma ( Fig. 4f; P = 0.0033). This could represent a shared affinity for galls with similar characteristics or a currently unknown trophic association between Ormyrus and Eurytoma wasps (i.e., one is a parasite of the other).

Notes: As a genus, Ormyrus are ubiquitous in their phylogenetic, geographic, taxonomic, and ecological relationships with oak gall wasps. Though individual species are often apparently specialized on a small number of gall types ( Sheikh et al. 2022), they may be able to use any of several insect species within a gall as their host, or act as inquilines, or some combination thereof. Understanding host breadths and life histories of individual Ormyrus species alongside their phylogeny will be critical to understanding how and under what circumstances oak-associated Ormyrus have diversified.

Figures

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.