Cooke-Mcewen, Crystal & Gates, Michael, 2020, Contributions to Disholcaspis Dalla Torre And Kieffer (Hymenoptera: Cynipidae: Cynipini), Zootaxa 4859 (3), pp. 355-382: 363-365

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Morphology of Disholcaspis  

Asexual generation wasps: The traits that differentiate Disholcaspis   sensu stricto from other genera are as follows: Mesosoma ( Fig. 4–5 View FIGURES 2–7 ). Notauli incomplete anteriorly; scutellar foveae generally absent or not well defined, scutellum sometimes with anterior transverse impression in the place of foveae; propodeal carinae fragmented and curved to nearly form a ring or absent. Metasoma ( Fig. 6–7 View FIGURES 2–7 ). Setation on metasoma generally limited to patches laterally on the second tergum; extended portion of the hypopygial spine tapering and is at most 4.5 times as long as wide; hypopygial spine with long subapical setae that reach beyond the apex of the spine but never form a dense, truncate tuft.

Variation and exceptions: Disholcaspis corallina (Bassett)   , D. plumbella Kinsey   , D. washingtonensis (Gillette)   , and D. arizonicus (Cockerell)   are exceptions to the setation on the metasoma with all terga setose. As noted by Melika and Abrahamson (2002) there was a subset of species that differ from the rest of the genus morphologically. This subset included D. chrysolepidis (Beutenmuller)   , D. conalis Weld   , D. corallina   , D. lasia (Ashmead)   , D. plumbella   , D. reniformis (McCracken and Egbert)   , D. spectabilis (Kinsey)   , D. sulcata (Ashmead)   , and D. washingtonensis   . Disholcaspis arizonicus   morphologically agrees with some of the species in this subset and should also be included. Melika and Abrahamson thought that this subset all had the hypopygial spine as broad throughout its entire length and the length of the extended portion of the spine appearing equal to or less than its width. The shape of the hypopygial spine in some of these taxa were examined using SEM imaging and the shape of some was found to be more complicated than originally thought. The species D. corallina   , plumbella   , and washingtonensis   have the hypopygial spine laterally bulbous basally followed by a very short parallel-sided thinner section ( Fig. 8 View FIGURES 8–10 ). The species D. sulcata   , lasia, and arizonica may also have similarly shaped hypopygial spines, but they were difficult to see and the lateral sections were not as bulbous as in the spines of the previous three species. The species D. chrysolepidis   , conalis   , and spectabilis   have convexly tapering spines that are about as long as wide ( Fig. 9 View FIGURES 8–10 ). The shape of the hypopygial spine of D. reniformis   has not been examined. The two species D. lasia   and chrysolepidis   were grouped together in recent phylogenies ( Nicholls et al. 2017; Cooke-McEwen et al. unpublished) but they differ in the shape of the hypopygial spine.

Gall morphology: Disholcaspis   sensu stricto asexual generation galls are generally characterized as being monothalamus, detachable, woody, twig or root galls ( Figs. 2, 3 View FIGURES 2–7 , 47 View FIGURES 42–47 , 48 View FIGURES 48–53 ) with few exceptions. As with most gall wasps, the morphology of Disholcaspis   galls is generally species specific on a given host plant and is often the only diagnostic trait for identifying species. In some species many galls develop in close approximation, while galls of other species develop singly. Some Disholcaspis   species are known to induce the host to secrete nectar (sometimes referred to as honeydew) from the outer gall surface of asexual galls. Functionally this is hypothesised to induce a mutualistic relationship with ants that tend the galls as a result ( Inouye and Agrawal 2004, Nicholls et al. 2017, Seibert 1993). The sugary secretions can also attract stinging wasps, which can be problematic in domestic horti- cultural settings ( Eckberg and Cranshaw 1994). Fagaceae   including oaks generally don’t have floral or extrafloral nectaries ( Bernardello 2007; Taylor et al. 2012; Weber and Keeler 2013) and, at least in southern-hemisphere galls produced by other insects, no nectar-producing structure is associated with the gall tissues, so these secretions may not be analogous to extrafloral nectaries. Instead it has been proposed that these secretions are more functionally similar to arthropod honeydew secretions ( Aranda-Rickert et al. 2017). The induction of nectar secretions and the galls themselves are thought to be part of the extended phenotype of the gall wasp ( Nicholls et al. 2017; Stone and Cook 1998; Stone et al. 2002).

Unlike the asexual generation galls, the sexual generation galls have been found to be very similar between species with the galls looking similar to buff-colored grains of rice that are located in or near the meristem of the leafing buds in the early spring. The spring galls often disfigure the newly developing stem making it shorter and the new leaf petioles will often curl around the gall making it difficult to see the gall without spreading or removing the leaves ( Fig. 10 View FIGURES 8–10 ).