Sawflies ( Hymenoptera , Symphyta ) of three Mid-Atlantic Parks in the George Washington Memorial Parkway

A diverse sawfly fauna of 176 species in 66 genera in 10 families occurred in three parks in the George Washington Memorial Parkway – Dyke Marsh Wildlife Preserve (DMWP), Great Falls Park (GFP), and Turkey Run Park (TRP). Adult sawflies flew from early March through mid-November. They included the rarely-collected Kerita fidala Ross, a leafminer of Mertensia virginica (L.) Pers. ex Link (Boraginaceae) and an unidentified Caliroa sp. which consumes Staphylea trifolia L. (Staphyleaceae). Nine of the collected species are alien ones in North America. Based on coefficients of community, DMWP was more similar to TRP than GFP, and GFP and TRP were more similar to one another than to DMWP. In DMWP, most species were uncommon in samples. Ninety-five percent of the reported host genera of the collected sawfly species occurred in all three of the parks.


Introduction
Symphyta (sawflies) is a hymenopteran suborder of about 9,000 species in about 1,000 genera in 14 families (Taeger et al. 2010), which occurs in many terrestrial habitats worldwide.Sawfly larvae consume foliage, stems, and wood, and adults consume leaf pubescence, nectar, other insects, water, or a combination of these things, depending on the species (Smith 1979(Smith , 1993)).Larvae are external leaf feeders, gall-formers, leafminers, and stem-and wood-borers of a diverse flora of mosses, ferns, conifers, and herbaceous and woody flowering plants.Most sawfly species are larval specialist feeders of one or a few plant genera, except larval Orussidae which parasitize wood-boring beetles.Some sawfly species can cause significant economic damage to agricultural crops, forests, and ornamental plants.Larvae of these species, either as defoliators, stem borers, or wood borers, can reduce growth of plants, even killing them.In the U.S. mid-Atlantic area, adults fly from March through October, with most species flying in spring and early summer.
Our goal is to ascertain sawfly species identities, flight times, and abundances in three parks within the George Washington Memorial Parkway (GWMP).Our samples are from Townes-style Malaise traps (Townes 1972) and hand-collecting in a rare, tidal, freshwater marsh; a floodplain forest; a swamp; and an upland forest in the Piedmont and Coastal Plain geological provinces -Dyke Marsh Wildlife Preserve (DMWP), Great Falls Park (GFP), and Turkey Run Park (TRP), in Fairfax County, Virginia.Our research questions include (1) which species are present in each park, (2) how similar are the species compositions among parks, (3) what are the species flight periods, and (4) more specifically, what are the species and their abundances in three habitats of DMWP?To our knowledge, this is the second-most comprehensive study of sawflies of a U.S. park administered by the National Park Service.Further, this is the first study of a park that occurs in two geological provinces or has a rare, freshwater, tidal marsh.

Methods
The GWMP comprises 2,984 ha of roads and roadsides, land, and water in the Potomac River Valley on the western side of the river from the Great Falls area south to Mt. Vernon, Virginia and on the eastern side of the river from Glen Echo, MD through Georgetown in Washington, D.C. (Fig. 1).Great Falls Park (323 ha) and TRP (312 ha) are in the northern part of GWMP in the Piedmont Province, and DMWP (154 ha) is in the southern part of GWMP in the Coastal Plain Province.Johnston (2000) described DMWP, and Steury et al. (2008) described the flora of GFP in detail.The GWMP contains many habitats including upland forest; flood-plain forest; swamp forest; freshwater, tidal marsh; mowed areas along its heavily-traveled parkway; and open park areas.This park has a rich biota of perhaps at least 20,000 species of ar-chaeans, bacteria, and eukaryans, including over 1,300 vascular-plant species.(Johnston 2000, Steury 2011, Barrows and Kjar 2014, pers. obs.).Further, the GWMP has several undescribed insect species and at least 58 rare, threatened or endangered animals and plants.
We sampled DMWP from April 1998 through December 1999 with six Townesstyle Malaise traps (Townes 1972), two in each of three habitats (open marsh, floodplain forest, and ecotone) as described by Barrows et al. (2005).We sampled GFP and TRP in 2006 through 2009 from mid-March through mid-November with Townes-style Malaise traps, supplemented by hand-collecting.In GFP, we ran one trap in each of three habitats -quarry site, Great Falls Swamp, and in the upland forest by Mine Run.In TRP, we ran one trap in an upland forest and two traps in the floodplain forest near and just upstream from the mouth of Turkey Run.We ran traps long enough each year to obtain entire sawfly seasonal records.In DMWP, we ran traps in the same places in 1998 and 1999.In GFP and TRP, we moved traps within their habitats from year to year to increase the sawfly diversity in our samples and obtained about 72 samples per year for both parks combined.Although Malaise traps obtain biased samples, they are the single best method for collecting and surveying for sawflies.In the mid-Atlantic area, visual searches for sawflies in nature usually do not discover many species.
For DMWP, we extracted all sawflies from samples for quantitative analysis of numbers of adults of each species and their abundances and flight times in the three study habitats.For GFP and TRP, we extracted all sawflies from samples to determine the number of species and their flight times in both of these parks.Over 10,000 specimens were collected during this study.To calculate coefficients of community, we used the formula CC = 2c/(a + b), where c = the number of species that pairs of parks have in common, a = the species richness of park-1, and b = the species richness of park-2 of the comparison.
Voucher specimens are deposited in the GWMP Arthropod Collection at TRP and duplicate material is held in the Georgetown University Arthropod Collection and the National Museum of Natural History, Smithsonian Institution, pending cataloging in the NPS ReDiscovery database and processing of loan agreements.

Species richness
We found a diverse sawfly fauna of 176 species in 66 genera in 10 families in GWMP which consume at least 57 genera of angiosperms, ferns, gymnosperms, and horsetails (Table 1).These sawflies include a rarely-collected species (Kerita fidala Ross) recorded as a leafminer of Mertensia virginica (L.) Pers.ex Link (Boraginaceae) and an unidentified Caliroa sp. which consumes Staphylea trifolia L (Staphyleaceae) and is still known only from larvae.Both sawfly species were collected in the floodplain near Turkey Run.The record of K. fidala is the first for Virginia (Smith 2009).Nine of the collected species are alien in North America.Ninety-five percent of the reported plant host genera of the sawfly species that we caught occurred in all three of the parks.
We found 69 species in DMWP, 134 in GFP, and 115 in TRP.Twelve species were unique to DMWP, 43 to GFP, and 22 to TRP.Forty species were found in all three parks.Coefficients of Community (CCs) for GWMP ranged from 0.49 through 0.68 (Table 2).Dyke Marsh Wildlife Preserve was more similar to TRP than GFP, and GFP and TRP were more similar to one another than to DMWP.Acordulecera pellucida (Konow).GFP, TRP.May-September.Probably several generations a year (Smith and Barrows 1987).Family Tenthredinidae.This is the largest and most diverse sawfly family in numbers of species, host plants, and habits.Larvae of most species are external leaf feeders, and a few are leafminers and gall formers, as noted below.All six tenthredinid subfamilies occurred in GWMP.

Flight periods
As a group, GWMP sawflies flew from early March through mid-November.With regard to species richness and month, more species occurred in April through June than in other months, with species numbers peaking in May in each of the three parks and for all parks combined (Fig. 2).In DMWP, the number of individuals peaked in early June 1998 and early May 1999.
Of the 176 species collected, 138 have a single emergence period in the spring, March through June, indicting a single generation a year.Another 12 species apparently with only a single generation fly only from mid-summer through October, with only 3, both species of Metallus and Tremex, occurring as late as September and October.The remaining 26 species occur through much of March or April through September and are probably multivoltine.Species of two genera, Allantus and Taxonus are apparently bivoltine, with a large emergence in the spring and a small emergence in late summer or early autumn.

Discussion
Our GWMP sawfly survey is the second largest survey of a U.S. park administered by the U.S. National Park Service.Smith (2008) reported on the largest such survey in the Great Smoky Mountains National Park.

Species richness
We found 176 sawfly species in the GWMP; however, this biotically-rich location might harbor over 200 species.A similar study of species abundance and diversity in two oak-pine forests in Virginia and West Virginia using Malaise traps estimated that 81% of the actual species present were captured over a five-year period (Braud et al. 2003, Strazanac et al. 2003).We expected to find more diprionid species and species of conifer-feeding siricids.We found three Acordulecera species, but more are expected once taxonomic problems are resolved.There are several reasons why we did not find more species in our survey.Malaise traps are biased toward strong flying species such as Taxonus and Macrophya; species that are weak flyers or stay close to their host plant are not often collected in traps.Some mid-Atlantic species are rare or not expected in GWPM.Immature stages of many species are very difficult to find in nature.Adults of some species tend to be in places such as near their hosts or in treetops where we did not site our traps.More intense sampling in already-sampled habitats and sampling of additional unsampled GWMP habitats could obtain more species.Unsampled GWMP sites include areas in Montgomery Co., Maryland, and the District of Colum- bia, as well as sites with Pinus and Salix, the floodplain forest of Theodore Roosevelt Island, the Clara Barton Parkway in Maryland, and the George Washington Memorial Parkway in Virginia, where these roads border and run through the GWMP.
The GWMP sawfly fauna is 50% of the 351 sawfly species recorded for the entire state of Virginia (Smith 2006(Smith , 2013)).In comparison, Smith and Barrows (1987) found 85 species in samples from less natural Maryland habitats using two sets of Malaise traps 0.8 and 1.5 km from TRP. Seventy percent of these species are also in our samples from the three GWMP parks.There are 91 recorded species for Plummers Island, Maryland, located across the Potomac River from TRP (Smith 2008).In another Virginia Coastal Plain site, D. R. Smith (unpublished)

Abundance, distribution, and flight periods
Flight times and numbers of adult sawflies can vary from year to year as occurred in the DMWP samples.Factors including distribution of host plants, adult foods, and mates; drying winds; natural enemies; soil moisture and temperature; and weather affect adult abundances, distributions, and flight periods (Wallace and McNeal 1966), subjects not yet studied in DMWP.

Sawfly abundance and distribution in DMWP
The causes of the sawfly abundance and distribution in DMWP are not yet studied.Our plot of frequency of specimens versus species (Fig. 4) shows that the majority of species were not common in our samples.Smith and Barrows (1987) found a similar relationship in their sample from a less natural area and a yard in the Washington, D.C., area.Low numbers of specimens of many species may have occurred in our sample because of factors such as a species' being rare, rare individual's of more common species straying into our study site from elsewhere, and a species' flight habit precluding our trapping the species.In DMWP, adult sawflies were more common in 1998 than in 1999 based on trap samples, as also occurred in other DMWP insects such as fireflies (Barrows et al. 2008) and mecopterans (Barrows and Flint 2009).In contrast, DMWP rhopalosomatids (Barrows 2013) and sialids (Barrows et al. 2005) were more frequently captured in 1999 than in 1998.
In summary, we found a rich fauna of 176 sawfly species which feed on many plant genera in the GWMP, and as a group, the sawflies flew from early March through November.Sawfly species in DMWP were most common in its ecotone, followed by its forest and marsh, and these species greatly varied in abundance.In this time of worrisome, rapid global change, threats to the GWMP include air, soil, and water pollution; many alien, invasive species; flooding; and erosion (Litwin et al. 2013, pers. obs.).In fact, DMWP is losing about 0.6-0.8hectare per year due to erosion.The National Park Service may restore the marsh to some extent in this decade.Increased marshland from restoration could change the mean population sizes of some the DMWP sawfly species.Since Symphyta is a species-rich, GWMP taxon, it is an appropriate one for monitoring GWMP's health in forthcoming years.This large, wasp suborder is an understudied animal taxon, and myriad aspects of the biologies of GWMP and other species are ripe for investigation.

Figure 1 .
Figure 1.Locations of sawfly sampling sites.Dyke Marsh Wildlife Preserve, Great Falls Park, and Turkey Run Park within the George Washington Memorial Parkway (GWMP) in Virginia.

Table 2 .Figure 2 .
Figure 2. Number of sawfly species versus month in the GWMP, Virginia.Diamonds represent sawfly numbers in DMWP; squares, GFP; triangles, TRP; and circles, all three parks combined.

Figure 4 .
Figure 4. Number of species versus number of individuals captured in the DMWP sample.In addition, one species had 58, one had 84, and one had 251 individuals which are not shown on this graph to conserve space.

Table 1 .
An annotated list of sawfly taxa of GWMP with fight periods based on our samples, parks in which species occurred, known species host plants, and other notes † .
found 175 species in Essex Co. based on 10 years of sampling.In other Virginia Piedmont sites, he found about 200 species in the University of Virginia Blandy Experimental Farm and State Arboretum of Virginia, Clarke Co., based on 6 years of sampling; 175 species in Bull Run Mountains Conservancy, Prince William Co., in 3 years; and 125 species in a his suburban yard in Fairfax Co. in 33 years.