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III. Ecological Observations on Tachysphex pechumani (Hymenoptera: Crabronidae)
Erin K. Moan and Elliot J. Tramer

Northeastern Naturalist, Volume 15, Monograph 2 (2008): 67–76

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2008 NORTHEASTERN NATURALIST 15(Monograph 2):67–76 III. Ecological Observations on Tachysphex pechumani (Hymenoptera: Crabronidae) Erin K. Moan1 and Elliot J. Tramer2,* Abstract - This study addressed aspects of the ecology of Tachysphex pechumani (antenna-waving wasp), a rare solitary wasp. Wasps nested in compacted sand, primarily where vegetative cover was 5–30% and vegetation height was 0.5 to 33 cm. Miltogrammine flies and predators presented challenges to wasp success at the study sites. The timing and duration of T. pechumani’s breeding season conformed to an apparent abundance peak of acridid grasshopper nymphs used by wasps, based on sweep-net data. Heat increased wasp activity to an upper threshold of 56 °C at the sand surface, at which temperature wasps ceased working. Weak flying abilities of both sexes suggested that populations were effectively isolated and vulnerable to habitat loss or fragmentation. Management for wasps should include maintenance of open sites and prohibition of sand disturbance. Introduction Tachysphex pechumani Krombein (antenna-waving wasp) is a rare insect that inhabits partially exposed sandy soils characteristic of oak savanna and pine barrens. It is distinguished from other Tachysphex wasps by its brassy golden face and orange apical antennal segments, which are incessantly waved up and down. The 8.3–12.1 mm female wasp is predominantly black with two or three red basal abdominal segments; male wasps may be 6.0–9.7 mm and are entirely black (Kurczewski et al. 1970). Adults appear for approximately five or six weeks surrounding the summer solstice. Males are observed for only about a week, hovering near and mating with females as they emerge. Females live three to four weeks; after mating, they hunt and provision burrows. A female wasp paralyzes an immature grasshopper (primarily of the genus Melanoplus), drags it back to a previously dug burrow, lays a single egg on it, and fills in the burrow (Kurczewski and Elliot 1978). Because this animal requires expanses of barren sandy soil free of overhanging vegetation, T. pechumani may be a good “indicator species” for oak savanna ecosystems, which are rapidly disappearing due to land development and fire suppression. As its required habitat disappears, the wasp’s existence may become precarious. Although the antenna-waving wasp’s life history and geographic distribution have been previously studied, there is much to be discovered regarding this rare animal’s ecology. Conservation biologists have specified several characteristics of a species at high risk of extinction (Meffe et al. 1997), and these characteristics 12554 Township Road 444, Sugarcreek, OH 44681. 2University of Toledo, Department of Environmental Sciences, MS 604, Toledo, OH 43606. *Corresponding author - ETRAMER@UTNet.UToledo.Edu. 68 Northeastern Naturalist Vol. 15, Monograph 2 fit the antenna-waving wasp. One characteristic is limited geographic range or highly localized populations. Tachysphex pechumani is limited to areas of southern Ontario, the lower peninsula of Michigan, the Oak Openings region of northwest Ohio, New Jersey Pinelands National Reserve, and northwest Indiana (Kurczewski 1998, 2000). Another characteristic of species at risk is small population size. Small populations tend to lose genetic diversity over time, leading to increased probability of extinction. Tachysphex pechumani population sizes are generally unknown. However, at least in the Oak Openings region, patches of sand suitable for burrowing by T. pechumani are small and widely scattered. Furthermore, observations of nesting wasps (Kurczewski 1998, Kurczewski and Elliot 1978) suggest that T. pechumani may be a weak flyer. If so, poor dispersal ability would limit movement between sites and restrict the wasps’ ability to find other suitable nesting sites if their home site is destroyed or overgrown. In the Oak Openings region, T. pechumani may be especially at risk due to human activities. Conversion of Oak Openings habitats to residential and commercial development is proceeding rapidly, and sandy openings in protected areas have experienced closure by invading woody vegetation. Tachysphex pechumani has not been reported in Ohio outside the Oak Openings and is considered “endangered” in the state (Kurczewski 1998). Our study is aimed at improving understanding of its ecology and suggesting proper habitat management for its benefit. One goal of our study was to characterize T. pechumani burrow sites in terms of vegetation structure and prey density. We also questioned why wasps restrict their mating and nesting to such a short time period (early June to mid-July). Hypothesizing that wasp activity might be limited by temperature, we investigated the effect of heat on wasp activity. We also asked whether the timing of adult wasp activity corresponded with seasonal prey density, an idea suggested previously by Kurczewski (1998). An important question is whether T. pechumani subpopulations are part of a larger, interbreeding metapopulation, whose members disperse readily and create gene flow. If so, small subpopulation sizes would be less of a concern. Since oak savanna is being rapidly lost to land development and fire suppression, it is also valuable to know whether wasps could disperse to new habitat if an occupied site is destroyed or overgrown. Finally, it was important to identify what management techniques might provide and maintain suitable T. pechumani habitat. Since the wasp is designated as endangered in Ohio, it is important that individuals and organizations know how best to protect remaining T. pechumani populations. Materials and Methods Our study location was Oak Openings Preserve Metropark in Lucas County, OH. From the park’s 12 known T. pechumani sites, we chose three that appeared to contain the largest numbers of wasps, estimated from casual observation in 2001. One site (“Monclova;” 41º33'27"N, 83º51'35"W) was a utility road turnaround near an old sand quarry. Wasps nested in compacted 2008 E.K. Moan and E.J. Tramer 69 sand directly in the track. The second and third sites (“Tansel Lane;” 41º34'12"N, 83º51'35"W) were in a sandy opening adjacent to a Prunus serotina Ehrh. (black cherry)/ Quercus velutina Lam. (black oak) woodland. The opening contained two nesting sites, “Tansel East” and “Tansel West,” separated by about 20 m of low, shrubby vegetation. The distance between Monclova and the two Tansel sites was approximately 2.1 km. We began recording temperature on June 7, 2002, utilizing a CR10X datalogger (Campbell Scientific, Logan, UT) with a thermister placed at a depth of 30 to 40 mm, which is Tachysphex pechumani’s burrow depth (Kurczewski 2000). The datalogger recorded the temperature every 30 minutes for the entire 2002 field season. In 2003, mercury laboratory thermometers were placed in direct sun on the sand surface whenever researchers were at wasp sites. This method may have given a temperature that differed somewhat from actual “sand-surface temperature,” normally measured with a shaded sensor, as the sun may have heated the mercury in the thermometer more or less than it was heating the sand—thus the actual measurement taken represents the net effect of heat flow by conduction between the sand and the thermometer bulb and the heating of the thermometer bulb by solar radiation. We adopted this method to attempt to approximate the temperatures the wasps were actually experiencing, since their bodies were not shielded from direct sunlight. For convenience, here we refer to these temperatures as “sand-surface temperatures.” Every 15 minutes, temperatures were recorded and notes were taken on wasp activity or absence. Temperature from lab thermometers was also noted when a wasp appeared dragging prey, and again when she stuffed the grasshopper into her burrow. To characterize vegetation at T. pechumani burrow sites, vegetation structure was surveyed over a time span of three days at the conclusion of the first season (July 3–5, 2002). We used a meter square, centered on the burrow entrance, to estimate percent vegetative cover. We also measured the tallest individual of each species present. Twenty-three squares were sampled at Monclova, 18 at Tansel west, and 6 at Tansel east. Prey density and size were investigated May 30 through July 19 of 2002 via sweep netting. A 30-cm diameter insect net was swung along the same transect through three areas used by the wasps for hunting. The vegetation along the sweep routes was low (maximum height 30 cm), within the range of heights used by wasps foraging for prey (Kurczewski 2008). Each site was sampled six times (approximately every 14 days). Grasshoppers caught were measured and the species recorded if known. Only acridid species used by the wasps were tallied; “long-horned” grasshoppers and individuals of the genera Spharagemon and Dissosteira were released. Kurczewski (1998) speculated that the wasp’s lifespan corresponds with peak abundance of potential prey grasshoppers. Sweep-net data were used to determine the seasonal pattern of abundance of T. pechumani potential prey. We compared grasshopper sweep-net data with grasshoppers caught and then abandoned by antenna-waving wasps. Wasps frequently abandoned 70 Northeastern Naturalist Vol. 15, Monograph 2 paralyzed prey for a variety of reasons (see results). Thus, we were able to collect grasshoppers taken by wasps without removing them from the wasps’ burrows, a procedure we wished to avoid because of T. pechumani ’s endangered status. We assumed that abandoned prey represented a random sample of grasshoppers being caught by the wasps, thus reflecting the size range of captured prey. Based on our observations, we are confident that this assumption is valid. To determine effect of temperature on wasp behavior, the number of completed burrows each day was compared with the daily maximum temperature (typically occurring between 1500 and 1700 hours) and also with the temperature at 1100 hours, which appeared to be the peak of daily wasp activity. Temperatures used were those recorded by the CR10X datalogger. Wasp marking was performed in both field seasons. Females were netted, placed in vials on ice within a cooler to render them temporarily inactive, then marked between the bases of the forewings with nontoxic, permanent Faskolor paint (Parma International, North Royalton, OH). Wasps were returned to the cooler to allow the paint to dry, then released after a brief warm-up period. Care was taken to avoid applying paint on wing bases, where it might interfere with flight, or on the abdomen, where it could interfere with breathing through the spiracles. Marked wasps behaved normally and similarly to unmarked wasps. In 2002, wasps were marked as early in the season as possible using a different color for each subpopulation to determine if dispersal occurred among females of different subpopulations. All statistical analyses were performed using SAS Version 8 (SAS Institute 2000). Results and Discussion At our study sites, wasps nested in flat areas where sand was moderately compacted. Shifting dunes, slopes, and loose sand were not utilized by antenna-waving wasps for burrow sites. Percent vegetative ground cover for our sites ranged from 2% to 66%, with a mean of 19.8% and a median of 16%. Three-fourths (34 out of 45) of the data points fell between 5% and 30% cover (Fig. 1A). The height of surrounding vegetation ranged from 0.5 cm to 68 cm, with a mean of 23.6 cm, a standard deviation of 15.4 cm, and a median of 23.5 cm. Eighty percent (36 out of 45) of the values were between 0.5 cm and 33.0 cm (Fig. 1B). Plants occurring most frequently at study sites were Rumex acetosella Linnaeus (sheep sorrel), Krigia virginica Linnaeus (dwarf dandelion), Rubus flagellaris Willd. (dewberry), and many grasses, including a number of Panicum species. Adult wasps were first observed June 12 and June 14 in 2002 and 2003, respectively. Males were observed for several days hovering near burrow areas and mating with females. Ten to twelve days later, five to seven females were often observed simultaneously at our study sites, and many other females were hidden by surrounding vegetation as they hunted or returned with prey. Most females were gone by the July 4 of both years, but 2008 E.K. Moan and E.J. Tramer 71 occasionally a single wasp was observable at the sites throughout the first two weeks of July. After mid-July, no T. pechumani were seen. Antenna-waving wasps contend with many obstacles to successful reproduction. Antenna-waving wasps are subject to predation by Miltogrammine flies known as satellite flies. The flies wait at a burrow site until a wasp dragging prey appears, then attempt to dart in and lay their own larva on the grasshopper while the wasp is reopening its burrow. The fly larva searches Figure 1. A. Percent vegetative cover at Tachysphex pechumani (antenna-waving wasp) burrow sites in 2002. B. Maximum vegetation height (cm) at T. pechumani burrow sites in 2002. 72 Northeastern Naturalist Vol. 15, Monograph 2 for the wasp egg and destroys it before consuming the grasshopper (Spofford et al 1986). At least two species of satellite flies were observed at our study sites, and several of their pupal cases were discovered in soil from wasp areas. It is also possible that velvet ants (Mutillidae) are parasitoids of T. pechumani pupae; although no T. pechumani researcher has reported this, velvet ants are known to parasitize the pupae of other wasps, chewing a hole in the pupa case and then depositing their own egg inside (Evans and Eberhard 1970). Velvet ants were often seen at the study sites. Predators may also destroy wasp burrows—on one occasion a skunk excavated a sizeable hole next to a burrow marker at a site, possibly consuming the buried grasshopper with wasp egg attached. Shrews and moles may also eat buried grasshoppers. Finally, adult wasps may be preyed upon by Cicindela repanda Dejean (tiger beetles). On several occasions we witnessed tiger beetles lunging at female antenna-waving wasps. Wasps typically avoided the attacks by flying a short distance, in some cases causing the wasps to leave prey momentarily or abandon it completely. We also noted one case of direct mortality when a tiger beetle caught and ate a male antenna-waving wasp. We compared grasshopper sweep-net data with grasshoppers caught and then abandoned by antenna-waving wasps (Table 1). If a wasp could not find her burrow, failed to successfully reopen it, or was attacked by a tiger beetle, she abandoned her prey. The abandoned grasshoppers were 16 to 21 mm (mean = 17.6, n = 19) in length. Few sweep-netted grasshoppers exceeded 16 mm in length until June 16–18. By then, the sweep-netted grasshoppers averaged 18.7 mm long, with a range of 10 to 25 mm, which encompasses the entire abandoned grasshopper range. The sweep-net data from June 26 and 27 are also within the size range of the grasshoppers taken by antenna-waving wasps. However, by July 6, the mean grasshopper length had increased to 20.3 mm, almost exceeding the abandoned grasshopper size range. There was still a range of 17- to 22-mm grasshoppers present, but note that abundance had decreased—only 9 grasshoppers were caught on that date. Another interesting observation regarding prey was that immature shorthorned grasshoppers of the genera Dissosteira and Spharagemon were not taken by T. pechumani even though they were of ideal length. Nymphs of these two genera have a stiff mid-dorsal crest on the thorax. We hypothesize that T. pechumani is unable to straddle and sting these nymphs because of the Table 1. Abundance and size of grasshoppers sweep netted in 2002, compared with size of prey abandoned by Tachysphex pechumani (antenna-waving wasp) in both 2002 and 2003. Date N Range (mm) Mean size (mm) May 30 29 5–17 10.7 June 7 18 6–19 12.9 June 16–18 25 10–25 18.7 June 26–27 17 11–25 17.2 July 6 9 17–22 20.3 July 19 10 15–28 20.5 Abandoned 19 16–21 17.6 2008 E.K. Moan and E.J. Tramer 73 crest. It is interesting to note that adult Spharagemon and Dissosteira, which are far too large to be preyed on by the wasp, lack this prominent crest. Wasp provisioning activity peaked between 1100 and 1200 hours (Fig. 2A). There was a smaller peak of activity in the late afternoon around Figure 2. A. Time of day of Tachysphex pechumani (antenna-waving wasp) burrow completion in 2003. B. Surface temperature (°C) at time of T. pechumani burrow completion in 2003. 74 Northeastern Naturalist Vol. 15, Monograph 2 1600 hours, with a break inbetween. This bimodal daily activity pattern confirms Kurczewski’s (1998) observations. There was a significant positive correlation between the number of burrows completed in a day and that day’s high temperature at burrow depth (r = 0.61, p = 0.01, n = 16). Warmer weather appears to induce T. pechumani activity, at least up to a threshold. Our observations showed that T. pechumani began burrowing and hunting when surface temperatures warmed to between 25 and 30 °C. Wasps provisioned burrows most actively at 37 to 46 °C (Fig. 2B), but burrow provisioning continued until an apparent upper threshold of 56 °C was reached, usually in the early afternoon on sunny days. In some cases during hot afternoons, a wasp carrying prey would not leave the shade, but halted at the sun-shade interface. Wasps exhibiting this behavior made periodic dashes onto the sunny sand, but always returned quickly to rest again in the shade. One wasp carrying prey spent 64 minutes in this type of behavior, wandering in a 1.5-meter circle but unwilling to go into the sun, where the surface temperature was 57 °C at 1242 hours. She eventually did run onto the sunny sand, quickly opened her burrow, and then spent over 3 minutes (much longer than average) completing the burrow, since she frequently took time to hover over the sand, apparently cooling herself. Another wasp exhibited the same aversion to the sunny sand surface (surface temperature 56 °C), and abandoned her grasshopper after only 8 minutes at the sun-shade interface. Kurczewski (2008) noted that antennawaving wasp females leave nesting sites when surface temperatures reach 55 °C, an observation very similar to our own. Many female solitary wasps curtail their activities at temperatures in this range (O’Neill 2001). In 2002, we detected no movement of marked females between subpopulations. Even at the two Tansel sites, which were separated by only 20 m of easily navigable vegetation, no color-coded wasps were found at the neighboring site. We observed that antenna-waving wasps make mostly low, short flights for 5 meters or less before settling again on the sand to run or walk; Kurczewski (1998) and Kurczewski and Elliot (1978) also describe these flight patterns. In 2003, however, a wasp marked at the Tansel east site was sighted at the Tansel west site, 37.4 m from where it was marked. It exhibited typical hunting behavior, running over and under dried leaves amidst vegetation in an approximately half-meter area (Kurczewski and Elliot 1978). In two years of observation, this wasp was the only one seen at such a distance from its marking point. Based on our large number of observations of T. pechumani flight patterns, we suggest that their ability to disperse may be limited. If an antenna-waving wasp does possess limited dispersal ability, the conservation implications are serious. In the Oak Openings region, suitable wasp habitat occurs in small, isolated patches separated from one another by several km of unsuitable terrain. Additionally, in this area, habitat destruction due to development is an imminent threat to this wasp. If a site is destroyed during months when wasps are underground, there is no chance of survival. If this occurs during wasp nesting season, there would have to be appropriate habitat very close by for successful colonization to occur. 2008 E.K. Moan and E.J. Tramer 75 In addition, low gene flow may put small populations at risk from inbreeding even in appropriate habitat. It is unknown whether male T. pechumani disperse after emergence; however, their flight pattern appears as weak as that of females. If males did disperse, inbreeding would not be a concern, but dispersal of males alone would not save a population threatened by habitat destruction. More research is needed regarding antenna-waving wasps’ mobility and dispersal abilities. Canopy closure due to natural ecological succession is also a potential threat to wasp habitat, and would likely cause gradual dwindling of the population as less exposed sand was available for nesting. In the Oak Openings, active management by cutting and controlled burning is employed to prevent the incursion of woody vegetation into open sand barrens. Our observations suggest several conclusions about antenna-waving wasps’ habitat requirements. One necessity is full sun on the site for most of the day. Wasps were not active on overcast days or when the sand was wet. If a site had sun early in the morning, the sand dried quickly and wasps could begin digging. Shade did not appear to be completely detrimental, however, because in the hottest hours of the afternoon, wasps dragging prey used shaded areas to rest and cool themselves. Another habitat requirement is freedom from encroaching vegetation. During the wet, cooler summer of 2003, grass coverage expanded at two of the study sites, and wasps created fewer burrows in those areas than in the hotter, drier year of 2002 when grass growth was at a minimum. Most likely there is a natural cycle of expansion and reduction of wasp habitat as the weather cycles through wet and dry years. Light burning for vegetation removal should not be harmful to T. pechumani as long as it is not performed during nesting season; Kurczewski (1998) maintains that the wasp is adapted to light wildfires due to a life history as a savanna-dwelling animal. A third requirement for T. pechumani sites is prohibition of vehicle traffic, which is essential during nesting season (early June through mid-July). Light traffic during antenna-waving wasps underground phase is not detrimental, but any traffic which would cause sand to be churned up or displaced (such as all-terrain vehicles) should be prohibited year-round. In sum, a proactive management plan would include keeping an antenna-waving wasp site free from excessive overhanging vegetation that would shade the site, maintaining relatively open sand via controlled burning or lopping, and prohibiting vehicle traffic as mentioned above. These recommendations are similar to current land-management practice for the preservation of oak savanna, and will maintain suitable habitat for other savanna-dwelling plants and animals as well. Acknowledgments Financial support for this project was provided by Toledo Naturalists’ Association. We thank Frank Kurczewski for sharing his wealth of wasp knowledge and giving helpful advice, and Kevin O'Neill for acting as manuscript editor. We also thank John Jaeger and Metroparks of Toledo for not only permitting, but encouraging, 76 Northeastern Naturalist Vol. 15, Monograph 2 our research at Oak Openings Metropark. Naturalist Bob Jacksy of Metroparks contributed invaluable field observations, advice, and spectacular photographs. Dr. Deb Neher and Dr. Michelle Grigore gave guidance and assistance throughout the research process. We also thank field assistants Heather Iler, Brian Putman, Melanie McLaughlin, Mary Croy, and Ben Proshek for countless hours of wasp watching. Literature Cited Evans, H.E., and M.J.W. Eberhard. 1970. The Wasps. The University of Michigan Press, Ann Arbor, MI. 265 pp. Kurczewski, F.E. 1998. Distribution, status, evaluation, and recommendations for the protection of Tachysphex pechumani Krombein, the antennal-waving wasp. Natural Areas Journal 18:242–254. Kurczewski, F.E. 2000. First record of Tachysphex pechumani (Hymenoptera: Sphecidae) from Indiana. Great Lakes Entomologist 33:41–43. Kurczewski, F. 2008. II. Nesting behavior of Tachysphex pechumani (Hymenoptera: Crabronidae). Northeastern Naturalist 15(Monograph 2):33-66. Kurczewski, F.E., and N.B. Elliott. 1978. Nesting behavior and ecology of Tachysphex pechumani Krombein (Hymenoptera: Sphecidae). Journal of the Kansas Entomological Society 51:765–780. Kurczewski, F.E., N.B. Elliott, and C.E. Vasey. 1970. A redescription of the female and description of the male of Tachysphex pechumani (Hymenoptera: Sphecidae, Larrinae). Annals of the Entomological Society of America 63(6):1594–1597. Meffe, G.K., C.R. Carroll, and contributors. 1997. Principles of Conservation Biology. 2nd Edition. Sinauer Associates, Inc, Sunderland, MA. 729 pp. O’Neill, K.M. 2001. Solitary Wasps: Behavior and Natural History. Cornell University Press, Ithaca, NY. 406 pp. SAS Institute. 2000. SAS Software Version 8. SAS Institute, Cary, NC. Spofford, M.G., F.E. Kurczewski, and D.J. Peckham. 1986. Cleptoparasitism of Tachysphex terminatus (Hymenoptera: Sphecidae) by three species of Miltogrammini (Diptera: Sarcophagidae). Annals of the Entomological Society of America 79:350–358.