Nicholls, Stone, and E. A. Buss., 2013

Samacá-Sáenz, Ernesto, Egan, Scott P. & Zaldívar-Riverón, Alejandro, 2020, Species Diversity in the Braconid Wasp Genus Allorhogas (Doryctinae) Associated With Cynipid Galls on Live Oaks (Quercus: Fagaceae) Using Natural History, Phylogenetics, and Morphology, Insect Systematics and Diversity 4 (2020), No. 3, pp. 1-20 : 15-16

The Genus Allorhogas Sensu Stricto

Here we report a previously unknown diversity of species of the braconid genus Allorhogas that are part of the insect communities associated with cynipid galls present on species of Quercus subsection Virentes in the southeastern United States. Our study only included taxa from a restricted geographic region of this country. However, according to our examination of specimens of Allorhogas collected several decades ago in a number of localities in the United States (Supp Table S4 [online only]), we found that there are various species that remain to be described, and only a few have host plant and associated cynipid records. The only other species of Allorhogas previously described from United States is Allorhogas arizonensis (Ashmead) . This species was also reared from a cynipid gall on an unknown oak species in Arizona, United States ( Ashmead 1889). An undescribed species of Allorhogas from Argentina has recently been reared from galls made by a cynipid species on leaf buds of Prosopis sp. ( Fabaceae ) (J. J. Martínez, in preparation), and preliminary phylogenetic analyses based on UCE data have confirmed that is closely related to the species described here (Samacá-Sáenz, unpublished data).

Based on the wide geographic distribution of cynipid species in the Nearctic and Neotropical regions, their host plant associations, and the museum material mentioned above, we believe that the species of Allorhogas described here only represent the ‘tip of the

iceberg’ of a much higher species richness of this genus that is associated with gall wasps. However, discovering this species richness will not be an easy task, since our rearing records and previous collection efforts suggest that the Allorhogas species that are associated with cynipid galls on live oaks are rare, unlike most other hymenopteran parasitoid and inquiline taxa that also belong to the same communities of natural enemies ( Forbes et al. 2016, Weinersmith et al. 2020, Egan et al. unpublished data). This study thus highlights the importance of conducting more detailed, systematic field work to obtain reliable host associations and natural history information that help to disentangle the systematics and evolutionary history of the insect taxa that are part of gall-former communities.

Allorhogas has been of particular interest in recent phylogenetic studies along with other doryctine genera that apparently are exclusively composed of gall-associated species since they have shown to have various phytophagous strategies and are associated with several plant families. Previous phylogenetic studies based on few molecular markers (Zalívar-Riverón et al. 2014) and mitogenomic and UCE data ( Samacá-Sáenz et al. 2019) have confirmed the monophyly of the gall-associated doryctine genera, but have found that Allorhogas as a whole is polyphyletic. In particular, Samacá-Sáenz et al. (2019) recovered a main Allorhogas clade composed of species that are reported to be phytophagous together with the undescribed species delimited here that was reared from stem galls of C. quercusbatatoides . Since the type species of Allorhogas , A. gallicola , is morphologically similar to all the species described here, it is highly plausible that this generic name should be restricted to the members of the above main Allorhogas clade. However, additional taxonomic and phylogenetic studies are needed to clarify the composition and limits of this genus. Among the morphological features that are shared by the examined species of the main Allorhogas clade are an excavated frons and a slightly curved vein m-cu in the hind wing.

Species of Allorhogas Sensu Zaldívar-Riverón et al. (2014) with reliable biological records have been currently associated with 11 different plant families ( Moreira et al. 2017, Zaldívar-Riverón et al. 2018). Most of the described Allorhogas species have been confirmed or observed to be phytophagous with different feeding habits, including gall formers on seeds and ovules on floral buds ( de Macêdo and Monteiro 1989, Morales-Silva and Modesto-Zampieron 2017, Joele et al. 2019), seed predators ( Zaldívar-Riverón et al. 2018) or phytophagous inquilines of other gall-forming insects ( Moreira et al. 2017). It has been presumed that some species of Allorhogas may be parasitoids of other gall-forming insects (Martínez and Zaldívar- Riverón 2013), though this was not based on direct observations. Regarding the species of Allorhogas examined in this study, some of the specimens associated with the gall wasp C. quercusbatatoides were reared from stem galls that also had larvae of the lepidopteran genus Synanthedon (Sesiidae) (Egan et al., unpublished data). These observations are concordant with Gahan’s (1912) records of the type species, A. gallicola , associated with Synanthedon , and with Forbes and colleagues’ (2016) report of moths of the genus Sinoe (Gelechiidae) coexisting in the leaf galls induced by Be. treatae . Therefore, whether the species of Allorhogas reared from cynipid galls are parasitoids of the associated lepidopterans or inquilines of the gall-inducer cynipids still needs to be clarified.

Potential Host-Associated Differentiation in

Allorhogas

In phytophagous insects, evolution of reproductive isolation and sympatric speciation is sometimes related to host shifts, and therefore host-associated differentiation (HAD) represents a form of isolation by environment, the latter being represented by the host plant

( Matsubayashi et al. 2010, Antwi et al. 2015, Driscoe et al. 2019). This process also contributes to the consequent cascading HAD of the arthropod communities that are associated with the herbivores, where sequential speciation could occur across higher trophic levels ( Stireman et al. 2006, Forbes et al. 2009, Feder and Forbes 2010, Hood et al. 2015, Zhang et al. 2019b). At both levels (herbivore and parasitoid), new barriers to gene flow emerge in natural populations as a consequence of ecologically based divergent selection between environments, which is consistent with ecological speciation ( Nosil 2012).

Few studies have addressed the existence of HAD in members of Cynipidae , and less have explored this phenomenon within their associated insect communities. These studies, however, have revealed the existence of HAD both for the gall wasps and their parasitoids. For instance, the alternative use of the host oaks Q. virginiana and Q. geminata by the gall wasp Be. treatae has been revealed to act as a source of divergent natural selection and genetic differentiation, promoting speciation among gall wasp populations ( Egan et al. 2012a, b; Zhang et al. 2017; Driscoe et al. 2019; Hood et al. 2019). Egan et al. (2013) also showed the existence of parallel patterns of morphological and behavioral variation among host-associated populations of Be. treatae and D. quercusvirens , whereas Zhang et al. (2019b) reported parallel patterns of temporal differences in five gall wasp species and a gall-forming fly on the same set of host plants. In addition, this same study showed that host plant use was associated with phenological differences in parasitoid species attacking three gall wasp species ( Zhang et al. 2019b), whereas significant hostassociated genetic structuring was observed in Megastigmus dorsalis (Fabricius) (Torymidae) , a parasitoid wasp complex that attacks different oak galls ( Nicholls et al. 2018).

Our host association records and the analyses performed suggest that diversification in some of the delimited species of Allorhogas may have occurred due to HAD, since they were associated with an exclusive type of gall or to galls made by two cynipid species in the same organ. Al. gallifolia emerged from leaf galls made by An. quercuslanigera and Be. treatae . The former cynipid species induces fuzzy single-chambered leaf galls located on the underside of new leaves on the midvein alone or in close proximity to other galls ( Hood et al. 2018), whereas Be. treatae develops within single-chambered spherical leaf galls on the underside of newly flushed leaves ( Egan et al. 2013). On the other hand, Al. caulinarius was reared from stem galls of C. quercusbatatoides and D. quercusvirens , the former producing stem swelling-like galls, and the second developing individually or in clusters of detachable, spherical branch woody galls ( Bird et al. 2013). In addition, specimens of Al. bassettia were exclusively reared from galls of Ba. pallida , which forms concealed galls composed of compartments that run parallel to the bark of twigs ( Melika and Abrahamson 2007, Weinersmith et al. 2020). One new species described here, however, could be explained by allopatric speciation. Al. belonocnema was associated with leaf galls made by Be. treatae in oaks from a locality that is 560km distant from the Al. gallifolia populations in Texas, which represents a break in the genetic structure of the host oak populations ( Cavender-Bares et al. 2015). Further studies comprising a broad sampling of Allorhogas specimens along south and southeast United States is required to further address HAD and allopatric speciation events in this system.