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1 December 2009 Wolcottia (=Isohydnocera) Aegra (Coleoptera: Cleridae): Association with Grasses (Poaceae), Native Spartina spp. and the Introduced Eragrostis curvula, and Resemblance to Co-Occurring Pseudomyrmecine Ants
A. G. Wheeler Jr., Ian C. Stocks
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Wolcottia aegra (Newman) a narrow, elongate, brown clerid beetle about 4.3 mm long (Fig. 1) was described in the genus Hydnocera and later placed in Isohydnocera (Chapin 1917; Kolibáč 1998). Kolibáč (1998) synonymized Isohydnocera with Wolcottia, but Opitz (2002) did not follow that synonymy. We follow Kolibáč (1998) in recognizing Wolcottia (=isohydnocera).

Known only from the southeastern United States, Florida, Georgia (Peck & Thomas 1998), Mississippi (Lago et al. 2002), North Carolina (Davis & Gray 1966), and South Carolina (Kirk 1969, 1970), W. aegra generally is not well represented in collections, and its habitat and plant associations are little known. In Florida, Shelford (1963) collected it in Dec in semidry prairies of tall sawgrass (Cladium mariscus ssp. jamaicense (Crantz) Kükenth.; Cyperaceae) marsh near Miami, and Cuda et al. (2007) rarely encountered it during a survey of insects associated with the adventive torpedo grass (Panicum repens L.) near Lake Okeechobee. In Mississippi, an adult was swept from a saltgrass (Distichlis) meadow and another from Schrankia (Fabaceae; probably an incidental occurrence) on Point Clear Island (Lago et al. 2002). The beetle was found in North Carolina from May to Oct on Spartina patens (Ait.) Muhl. in salt marshes in Carteret County (Davis & Gray 1966). In South Carolina, Kirk (1970) swept W. aegra from “salt marsh grass” on Hunting Island, and 5 adults were collected at the Belle Baruch Marine Field Laboratory of the Hobcaw Barony, east of Geogetown, from late Apr to early May 2004, and another adult was taken at the same locality in mid-Sep 2007 (S. M. Paiero, Dept. Environmental Biology, University of Guelph, personal communication).

Fig. 1.

Alate of the pseudomyrmecine ant Pseudomyrmex seminole (top) and adult of the co-occurring myrmecomorphic clerid Wolcottia aegra (bottom). Scale line = 1 mm.

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Here, we report adults from 2 native grasses, sand cordgrass (Spartina bakeri Merr.) and saltmeadow cordgrass (S. patens), and an introduced African species, weeping lovegrass (Eragrostis curvula (Schrad.) Nees), and note the beetle's resemblance to syntopic pseudomyrmecine ants. From 2002 to 2009, an ax handle was used to beat the crowns of the 3 bunchgrass species into a shallow, short-handled net. Voucher specimens of the beetle are deposited in the Clemson University Arthropod Collection (CUAC) and National Museum of Natural History, Smithsonian Institution, Washington, DC; ants are deposited in the CUAC.

We collected adults of W. aegra in Florida, Georgia, and South Carolina from grasses at 14 sites (28 collections) during Jan, Feb, Mar, Apr, Jun, Aug, Oct, and Dec (Table 1). Of the 182 adults we collected, 7 were on S. patens and 71 were beaten from crowns of the more architecturally complex S. bakeri, which grows in dense clumps. The remaining 104 adults of W. aegra were collected in Florida from weeping lovegrass (E. curvula), an African bunchgrass used in the Southeast mainly for erosion control and slope stabilization. Wolcottia aegra can be included among the little-known or seldom-collected native insects that have become associated with weeping lovegrass (Wheeler 1999, 2003; Wilson & Wheeler 2005). We did not observe adults during the sampling of other coastal spartinas, smooth cordgrass (S. alterniflora Loisel.), and big cordgrass (S. cynosuroides (L.) Roth).

At one site, a highway embankment northwest of Loughman in Lake County, Florida, E. curvula and S. bakeri co-occurred. During about 20 min of sampling in mid-Mar 2007, split about evenly between the 2 grass species, 22 adults of the clerid were taken on E. curvula and 1 on S. bakeri.

In salt marshes, Davis (1978) considered W. aegra not abundant on, but “fairly characteristic” of, S. patens, a grass on which we found relatively few adults. One could infer from the scattered literature on this clerid that it is restricted to coastal marshes. We did find adults on S. patens in brackish flats and salt marshes and on S. bakeri in brackish and freshwater marshes along the coast. In Florida, however, we also found W. aegra in native populations and landscape plantings of S. bakeri in the Lake Wales Ridge in the center of the peninsula, as well as inland plantings of weeping lovegrass.

TABLE 1.

WOLCOTTIA AEGRA IN FLORIDA, GEORGIA, AND SOUTH CAROLINA, 2002–2009.

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Continued.

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We did not find clerid larvae on any of the 3 grass species. Trophic habits of other hydnocerine clerids are little known, but W. aegra has been assumed to be predacious (Davis & Gray 1966). Larvae of 2 other species of Wolcottia (=Isohydnocera) prey on endophages such as gall-inducing and stem-boring insects (Sabrosky 1934; Clausen 1940; Knull 1951). Potential prey of W. aegra on S. bakeri are stem borers known from other spartinas (Stiling & Strong 1984; White et al. 2005), including languriid beetles (Ward et al. 2007). We observed adults of Languria mozardi Latreille in several stands of weeping lovegrass inhabited by W. aegra.

Numerous species of Cleridae mimic aculeate Hymenoptera such as ants. Most hydnocerine clerids are generalized ant mimics, including species currently placed in Wolcottia (Mawdsley 1994).

We collected adults of W. aegra with the similarly colored pseudomyrmecine ants Pseudomyrmex pallidus (F. Smith) and P. seminole Ward (Fig. 1) on E. curvula and S. bakeri. After the presence of pseudomyrmecines began to be recorded in field notes (21 Mar 2007), 16 of 23 collections of the clerid also included one or both species of Pseudomyrmex. The clerid's resemblance to pseudomyrmecines was enhanced by an erratic antlike movement. Clerid males were about the same size as worker ants, whereas the larger females were about the same size as dealated queens. We found P. pallidus in Florida and South Carolina and P. seminole in Florida, Georgia, and South Carolina. Pseudomyrmex pallidus nests preferentially in stems of tall grasses (Van Pelt 1958), including salt marsh grasses (Carter 1962). Sympatric assemblages characterize the P. pallidus group. Pseudomyrmex seminole co-occurs with P. pallidus and might be a facultative social parasite of that species; it nests in dead stems of grasses, such as Andropogon spp. (Ward 1985).

Although the adult of W. aegra exhibits an antlike habitus, use of the more neutral term myrmecomorphy might be preferable to ant mimicry in the absence of data demonstrating that a resemblance to ants enhances survivorship of the clerid. Experimental studies documenting ant mimicry by W. aegra, and examining the possibility that adults are chemically protected, as are certain other myrmecomorphic Cleridae (Mawdsley 2002), are needed. Studies on bionomics of the clerid also are needed, especially information on larval feeding habits. Also desirable would be to determine whether ant densities on native Spartina species differ from those on the adventive weeping lovegrass and whether stems of these grasses differ in their suitability as nesting sites for pseudomyrmecines.

We thank Steven M. Paiero (Dept. of Environmental Biology, University of Guelph, Guelph, Ontario) for allowing us to refer to his collections of the clerid in South Carolina, and David R. Smith (Systematic Entomology Lab., USDA, ARS, Washington, DC) for identifying ants.

SUMMARY

Wolcottia (=Isohydnocera) aegra, an antlike or myrmecomorphic clerid beetle typically not well represented in collections, was associated with grasses at 14 sites (28 collections) in Florida, Georgia, and South Carolina. Adults (n = 182) were beaten from crowns of bunchgrasses; the introduced South African weeping lovegrass, Eragrostis curvula (n = 104), along highways; sand cordgrass, Spartina bakeri (n = 71), in coastal brackish and freshwater marshes and inland swales, as well as in landscape plantings; and saltmeadow cordgrass, S. patens (n = 7), in brackish flats and salt marshes. The ants Pseudomyrmex pallidus and P. seminole (Formicidae: Pseudomyrmecinae) co-occurred with the clerid.

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A. G. Wheeler Jr. and Ian C. Stocks "Wolcottia (=Isohydnocera) Aegra (Coleoptera: Cleridae): Association with Grasses (Poaceae), Native Spartina spp. and the Introduced Eragrostis curvula, and Resemblance to Co-Occurring Pseudomyrmecine Ants," Florida Entomologist 92(4), 648-652, (1 December 2009). https://doi.org/10.1653/024.092.0419
Published: 1 December 2009
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