Working List of Prairie Restricted (Specialist) Insects in Wisconsin (11/26/2015) By Richard Henderson Research Ecologist, WI DNR Bureau of Science Services Summary This is a preliminary list of insects that are either well known, or likely, to be closely associated with Wisconsin’s original native prairie. These species are mostly dependent upon remnants of original prairie, or plantings/restorations of prairie where their hosts have been re-established (see discussion below), and thus are rarely found outside of these settings. The list also includes some species tied to native ecosystems that grade into prairie, such as savannas, sand barrens, fens, sedge meadow, and shallow marsh. The list is annotated with known host(s) of each insect, and the likelihood of its presence in the state (see key at end of list for specifics). This working list is a byproduct of a prairie invertebrate study I coordinated from1995-2005 that covered 6 Midwestern states and included 14 cooperators. The project surveyed insects on prairie remnants and investigated the effects of fire on those insects. It was funded in part by a series of grants from the US Fish and Wildlife Service. So far, the list has 475 species. However, this is a partial list at best, representing approximately only ¼ of the prairie-specialist insects likely present in the region (see discussion below). Significant input to this list is needed, as there are major taxa groups missing or greatly under represented. Such absence is not necessarily due to few or no prairie-specialists in those groups, but due more to lack of knowledge about life histories (at least published knowledge), unsettled taxonomy, and lack of taxonomic specialists currently working in those groups. Likely underrepresented groups include many families of flies, micro-lepidoptera (families of moths with wingspans generally under 20 mm), some beetle families (such as weevils and leaf-beetles), parasitic and gall forming wasps, aphids, plant-lice, and more. Purpose of List The purpose of this list is to stimulate interest, among professional and amateurs alike, into looking for these species, so we may obtain a better understanding of their status and distribution, level of remnant-dependency, and host specificity. I also hope it will stimulate specialists and experienced amateurs to submit nominations for additions to the list. Over time, I anticipate species will not only be added, but some dropped, as we learn more about their ecology and habits. What are Prairie-dependent/specialist/restricted Insects? In conservation of prairies in the Midwest, there is often consideration given to prairie-dependent or remnant-dependent insects (or other invertebrates). Sometimes other terms are used to describe them, such as conservative, specialist, or restricted, but they all refer to the same general concept - a group of insects with a very tight, even dependent, relationship with native prairie. Sometimes the term “remnant” is used instead of “prairie” so as to include savanna, sedge meadows, and other communities closely associated with prairie. This is because there is frequent overlap in species among these linked natural area types. Specialist insects depend upon, and thus are rarely found outside of, remnants, or at least good quality restorations. Most often they are species that require a specific plant species, genus, or family at some point in their life cycle (they are host-specific or host- restricted) and in turn their host plants are primarily limited to remnants or restoration plantings. The group may also include specialized predatory or parasitic insects that require certain prey or hosts which are in turn associated with prairie vegetation. It may also include insects dependent upon other characteristics of the remnant prairie community, such as soil or substrate, which we do not yet understand. Unfortunately, for many insects we do not yet fully know what they eat or how host-specific they are in their needs. Assigning species, for which we have little or no host specificity information, to the prairie-dependent category is done based on survey work that has so far found them only on prairie remnants, or they have only been found within the former prairie region of the continent (per Metzler et al. 2005). Given our limited knowledge, classifying species as prairie-dependent can be difficult and subjective - it is certainly a work in progress. Following are a few examples that may help you better understand the concept. The monarch butterfly (Danaus plexippus), for example, is a well-documented host-specific insect. Its larvae, along with the larvae, adults, or both of a dozen other insect species, feed exclusively upon milkweed (Asclepias spp.), and most milkweed species are primarily limited to remnants and restorations. Thus, at first glance, milkweed feeders are seemingly good candidates for remnant-dependence classification. However, because there are two milkweed species, common and whorled milkweed, that regularly grow in abundance in non-remnant or non- restoration settings, such as roadsides, old fields, cropland, disturbed ground, etc., monarch butterflies, and the other milkweed specialist, do not fully qualify as remnant-dependent, even though they are very host specific. The Karner blue butterfly (Lycaeides melissa samuelis), on the other hand, is a good example of remnant dependence. Its larvae require wild lupine, a species highly associated with remnant sand savanna. Even though lupine may be found in sandy roadsides and sandy old fields, these are generally settings where native sand savanna or prairie vegetation is reestablishing from nearby remnant seed sources (much like a restoration). Therefore, unlike common or whorled milkweed, lupine are not widespread on the landscape. Therefore, most ecologists include the Karner blue in the restricted/specialist category. An even better example of prairie-dependency is the red-tailed leafhopper (Aflexia rubranura), which requires prairie dropseed (Sporobolus heterolepis) (as do five other prairie- restricted insects). This conservative grass is exclusively found in remnant prairie sod or restoration plantings. In another example, there are 9 species of moths that appear to only live on leadplant. Because of leadplant’s conservative nature (limited to remnants and plantings), these are all considered prairie-dependent insects. Of course not everything is so clear cut. For example, the tumbling flower beetle Mordellina impatiens, for which we know nothing about its host(s), so far has only been found in prairie and savanna remnants, thus it is currently catalogued as likely remnant- dependent. We also do not know what the moth Eoreuma crawfordi eats, but so far it is has only been found in prairie remnants, and all known locations are within the heart of the continent’s prairie region, so it is also considered a remnant-specialist for now. These are just a few examples as to why and how species were placed on to this working list. Why does it Matter? There are at least two useful applications for the concept of prairie-dependency. First, it has direct use in setting priorities for conservation actions. These restricted insects are now limited on the landscape and thus at greater risk of disappearing than most other species. Thus, knowing that such species are present on a site heightens its conservation significance beyond just the vegetation and rare plants that may be present. Even small remnant patches (1 acre or less) have proven themselves to be viable refuges for prairie- dependent insects. Second, some of the insects found on prairies (current estimate is 40%) have some level of sensitivity to fire (and other management activities). Although most of these do recover within one year, a small portion takes 2 or more years to rebound. Knowing which of these most sensitive of species are also remnant-dependent, and thus may have trouble recolonizing if lost from an isolated remnant, helps guide management decisions about how much to burn and how often. Just how many insects are prairie-dependent? Ron Panzer et al. (2010) estimated from their work in the Chicago area that approximately 15% of the insects using prairie remnants may be remnant-restricted. This translates into a conservative estimate of approximately 2,000 prairie-dependent insects in our region (WI, northern IL, eastern IA, and southeastern MN). Some of these species are highly mobile and produce many offspring each year and thus can find and colonize new prairie plantings or remnants within a year or two. Examples are the rosinweed metalmark moth Tebenna silphiella and most Silphium gall-wasp species (Antistrophus spp.). In fact, the widespread planting of prairie vegetation over the past 40 years in the upper Midwest has likely resulted in the resurgence of many of the more mobile prairie-dependent species. Other prairie-dependent insects, however, are more conservative, less mobile and slower to reproduce, and thus still remain quite rare on the landscape. These species may take decades to find new areas of habitat, such as restorations, and thus are the ones in greatest need of attention. As pointed out, our knowledge as to what species are truly prairie-restricted is limited. For some species, we have confidence in their host-specificity, and for others far less so, at least until more investigation and observation is done. For many of these species our knowledge of their status (population levels) and distribution is very limited. Needless to say, there is ample