Hymenoptera: Cynipidae) on the Roses of Canada’S Grasslands

251 Chapter 12 Galls Induced by Cynipid Wasps of the Genus Diplolepis (Hymenoptera: Cynipidae) on the Roses of Canada’s Grasslands Joseph D. Shorthouse Department of Biology, Laurentian University Sudbury, Ontario, Canada P3E 2C6 Abstract. Thirteen species of cynipid wasps of the genus Diplolepis induce structurally distinct galls on the three species of wild roses found on the grasslands of western Canada. Three species of Diplolepis gall the short rose, Rosa arkansana, in the Mixed Grassland and Moist Mixed Grassland ecoregions of southern Alberta and Saskatchewan, and eight species gall the common prairie rose, R. woodsii, throughout the prairie grasslands. Five species of Diplolepis gall the larger rose, R. acicularis, in more shaded regions such as the Aspen Parkland Ecoregion. This chapter outlines the life history strategy of Diplolepis and the manner by which these insects are well adapted to grassland conditions. Also described are the galls of each species, along with the component communities associated with them. Résumé. Treize espèces de cynipidés du genre Diplolepis engendrent la formation de galles structurellement distinctes sur trois espèces de rosiers indigènes des prairies de l’ouest du Canada. Trois de ces espèces de guêpes produisent des galles sur le rosier des prairies (Rosa arkansana) dans les écorégions des prairies mixes et des prairies mixtes humides du sud de l’Alberta et de la Saskatchewan, et huit autres s’attaquent au rosier de Woods (R. woodsii) dans l’ensemble de la région des prairies. Cinq espèces de Diplolepis engendrent des galles sur le rosier aciculaire (R. acicularis) dans les régions plus ombragées comme l’écorégion de la forêt-parc à trembles. Ce chapitre décrit les stratégies de survie des Diplolepis et la façon donc ces insectes se sont adaptés aux conditions caractéristiques des prairies. Il décrit également les galles produites par chacune de ces espèces, ainsi que les communautés qui leur sont associées. Introduction Grasslands of the three prairie provinces and valleys of the southern mountain regions of British Columbia support a diverse assemblage of flora ranging from lichens and mosses to grasses, forbs, shrubs, and trees. All of the more advanced plants are fed upon by numerous species of insects and, as the plants become more structurally complex, the kinds of insects increase, along with the roles they play and the niches they occupy (Strong et al. 1984). Hence, forbs have more species of associated insects than do grasses, shrubs have more than forbs, and trees have more than shrubs (Leather 1986). As a result, the kinds of feeding relationships that phytophagous insects have with their host shrubs are more complex than the relationships they have with grasses and forbs. Studying insects on shrubs has many advantages over studying them on trees. Shrubs are usually smaller than trees and the entire canopy can be sampled, whereas one risks life and limb trying to sample insects in the upper canopy of trees. Dozens of species of shrubs live in the grasslands of Canada’s prairies and British Columbia (Scoggan 1957; Looman and Best 1987; Moss and Packer 1983; Johnson et Shorthouse, J. D. 2010. Galls Induced by Cynipid Wasps of the Genus Diplolepis (Hymenoptera: Cynipidae) on the Roses of Canada’s Grasslands. In Arthropods of Canadian Grasslands (Volume 1): Ecology and Interactions in Grassland Habitats. Edited by J. D. Shorthouse and K. D. Floate. Biological Survey of Canada. pp. 251-279. © 2010 Biological Survey of Canada. ISBN 978-0-9689321-4-8 doi:10.3752/9780968932148.ch12 252 J. D. Shorthouse al. 1995; Brayshaw 1996; Harms 2003). The greatest diversity of shrubs on the prairies, especially in the Mixed Grassland Ecoregion in the south, occurs in areas with more moisture such as at the bottom of coulees; near creeks, potholes, and sloughs; and in the flood plains of rivers. Among the most common shrubs in the grasslands are wild roses. Three species of roses are found on the grasslands of the prairie provinces and one in the Okanagan grasslands. These species are host to insects in a variety of guilds, including leaf chewers, leaf miners, fluid feeders, stem borers, pollinators, and gall inducers (Shorthouse 2003). Plant galls and the insects that induce them represent the most complex insect–plant relationship found on grassland shrubs. Galls are atypical plant growths stimulated by the feeding activities of a select group of insects and mites that are considered by many as the most specialized arthropods in the natural world (see references in Meyer and Maresquelle 1983; Meyer 1987; Shorthouse and Rohfritsch 1992). Rather than chewing on plant tissues externally or internally and walking or tunnelling to new sites when food at one site has been exhausted, gallers are sessile and manipulate the growth and physiology of their host plants such that food comes to them. Gallers stimulate their host plants into providing them with highly nutritious plant cells normally not found in the attacked organ (Bronner 1992). New nutritive cells are continually produced as the older cells are consumed. The immatures of gallers are surrounded by these unique cells that not only provide food, but also shelter that protects them from the elements and from predators (Stone and Schönrogge 2003). Seven orders of insects have evolved the ability to induce galls. The most species-rich families of gallers are the Cecidomyiidae (midges) (Diptera) and the Cynipidae (cynipid wasps) (Hymenoptera) (Dreger-Jauffret and Shorthouse 1992). There are about 1,400 species of cynipids in the world (Csóka et al. 2005), with most found on oaks (Quercus spp.) and roses (Rosa spp.). All cynipid galls on roses are induced by wasps of the genus Diplolepis (= Rhodites of older literature) (Beutenmüller 1907). Amazingly, each species of cynipid induces distinct, anatomically complex galls (Stone and Cook 1998; Ronquist and Liljeblad 2001; Stone et al. 2002; Stone and Schönrogge 2003; Csóka et al. 2005) that develop from undifferentiated tissues of vegetative buds or immature stems. Galls are phenotypic and physiological extensions of the gall inducers (Dawkins 1982; Crespi and Worobey 1998; Stone and Cook 1998), with the insects, not the plants, in control of plant development. An important aspect in the biology of cynipids is that their galls attract many other insects that feed either on the tissues of the gall or on the larvae of the inducers. Numerous species of parasitoids have discovered the defenceless larvae of inducers within galls and have become major mortality factors (Brooks and Shorthouse 1998; Csóka et al. 2005). In addition to parasitoids, most species of Diplolepis are also attacked by inquiline cynipids of the genus Periclistus that kill the inducers and then alter the anatomy of inhabited galls (Shorthouse 1998). Each species of Diplolepis appears to have a characteristic assemblage of inhabitants associated with its galls. The purpose of this chapter is to describe the life history strategy of cynipids found on wild roses of the grasslands of Canada, illustrate the differences in their galls, and compare the communities of insect inhabitants associated with them. Roses of Canada’s Grasslands Roses are perennial woody shrubs in the family Rosaceae and are among the most successful and widespread shrubs in the northern hemisphere. They have an important ecological role in most terrestrial ecosystems south of the treeline and influence the biology Galls of cynipid wasps (Diplolepis) on grassland roses 253 Fig. 1. Schematic drawing of a typical prairie wild rose. Note that the shoot to the left is several years old and has side branches. The middle shoot is a sucker shoot and the shoot to the right is an adventitious shoot. All shoots are joined by rhizomes. of many animals, both invertebrates and vertebrates (Hatler 1972). The approximately 140 species of roses in the world form 10 taxonomic sections (Wissemann 2003). Wild roses are notoriously difficult to identify because of their variability and the ease with which they hybridize and yield fertile offspring (Lewis 1959). There are about 22 species of wild roses in North America (Erlanson MacFarlane 1966; Joly et al. 2006). Of the 12 species of endemic roses in Canada (Breitung 1952), only Rosa arkansana Porter, R. woodsii Lindley, and R. acicularis Lindley (section Cinnamomeae) (Wissemann 2003) occur on the grasslands of western Canada (Harms 1974; Moss and Packer 1983). 254 J. D. Shorthouse 2 3 4 5 6 7 Figs. 2–7. Wild roses of Canada’s grasslands and features of Diplolepis. Fig. 2. Rosa arkansana in early July near Coaldale, Alberta. Fig. 3. Rosa woodsii in early July in the Cypress Hills of southeastern Alberta. Fig. 4. Rosa acicularis at the forest edge in central Alberta. Fig. 5. Habitus of a female D. spinosa. Note the hypopygium extending from the ventral side of the abdomen. Fig. 6. Habitus of a male D. spinosa. Fig. 7. Full grown larva of D. spinosa. Photographs by the author. Wild roses are deciduous woody shrubs with erect stems (Fig. 1). They are ephemeral and long-lived and have many branches arising from the main stem, giving them a bushy appearance. The roots of some roses extend downward for 2 m, making them well adapted to dry grasslands. The upper parts of the root system send out numerous underground stems called rhizomes (Fig. 1) from which adventitious shoots develop when the above- ground parts of the shrub are eaten or killed by fire (Calmes and Zasada 1982). Roses quickly regrow from the rhizomes, even if large herbivores remove all above-ground parts. Increased bushiness, which is an adaptation to herbivore damage (Paige and Whitham 1987), Galls of cynipid wasps (Diplolepis) on grassland roses 255 leads to rose patches altering their microhabitats. Bushiness reduces wind, which benefits Diplolepis adults searching for oviposition sites. In addition, blowing snow accumulates in bushy rose patches, providing abscised leaf gallers with the relative warmth of a subnivean habitat (Williams et al.

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