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Cavity-nesting Wasps and Bees of Central New York State: The Montezuma Wetlands Complex
Kevin M. O’Neill and James F. O’Neill

Northeastern Naturalist, Volume 17, Issue 3 (2010): 455–472

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2010 NORTHEASTERN NATURALIST 17(3):455–472 Cavity-nesting Wasps and Bees of Central New York State: The Montezuma Wetlands Complex Kevin M. O’Neill1, * and James F. O’Neill2 Abstract - Solitary nest-provisioning wasps and bees in North America include species that naturally construct nests within existing cavities, such as hollow plant stems or tunnels left by wood-boring insects. The materials used to construct brood cells within nest cavities and the types of food provisions provided to offspring vary considerably among species. Over five summers (2001–2002, 2005–2007), we used trap nests to survey the cavity-nesting wasp and bee assemblage within the Montezuma Wetlands Complex in central New York State. Over 350 trap nests were occupied by 6 species of apoid wasps (Sphecidae, Crabronidae; 34% of nests), 7 vespid wasps (Vespidae: Eumeninae; 39%), 2 spider wasps (Pompilidae; 3%), and 12 bees (Megachilidae, Colletidae; 26%), as well as brood parasites and parasitoids of the nest provisioners. The most common nest-provisioning wasp was Trypoxylon lactitarse, followed by Ancistrocerus antilope, Isodontia mexicana, Symmorphus canadensis, Symmorphus cristatus, and Euodynerus foraminatus. The only two bee species with comparable incidences were Hylaeus annulatus and Heriades carinatus. Natural enemies emerging from nests included at least 17 species from 10 families, the most common of which were brood-parasitic cuckoo wasps (7 species of Chrysididae; 39 nests) and flies (Sarcophagidae; 11 nests). We also report brood sex ratios of the seven most abundant species, finding them to be either male-biased (A. antilope, T. lactitarse), female-biased (E. foraminatus), or not significantly different from unity. We compare our survey results to others done in north-central and eastern North America. Introduction Solitary aculeate bees and wasps construct nests in a variety of locations, using a wide range of nesting materials (Krombein 1967, O’Neill 2001). Some species build free-standing nests of mud attached to rocks, plants, or human structures. Others excavate tunnels in soil or plant materials, such as rotten wood or pith-filled plant stems. Finally, the so-called “cavitynesters” seek out existing cavities, commonly either hollow plant stems or tunnels left by emerging wood-boring insects. Cavity-nesting females usually modify nest cavities by adding partitions and plugs consisting, in different species, of mud, plant resins, fresh or dried plant materials, or debris gathered from the environment. Cavity-nesters have long been studied with the use of “trap nests”, whose basic design consists of either natural tubes made from hollow, dried plant stems or artificial tunnels such as paper straws or holes drilled in wood (Krombein 1967). Trap nests are relatively 1 Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, MT 59717; 2188 Woodlawn Avenue, Auburn, NY 13021. Corresponding author – 456 Northeastern Naturalist Vol. 17, No. 3 inexpensive, and can be placed in large numbers in appropriate locations to provide nesting habitat for pollinators and biological control agents, aid in detailed biological studies of individual species, or survey local communities of cavity-nesters. Because of their habitat requirements, trophic diversity, and roles as plant pollinators and hosts of natural enemies, cavitynesters and other solitary nest-provisioners have been proposed as indicator species for environmental change, including the effects of invasive species (Barthell et al. 1998, Gayubo et al. 2005, Tscharnke et al. 2003). From 2001–2007, we used trap nests to conduct ecological studies of an assemblage of cavity-nesting wasps and bees and their insect natural enemies at the Montezuma Wetlands Complex (MWC) in central New York State. The MWC consists of ≈15,000 ha of public and private lands set aside to preserve wildlife habitat. Most of the land is situated in Montezuma National Wildlife Refuge (MNWR, administered by the US Fish and Wildlife Service) and the Northern Montezuma Wildlife Management Area (administered by the New York State Department of Environmental Conservation). Several of our biological studies on particular species in this area have been published (Jensen et al. 2007, O’Neill and O’Neill 2009, O’Neill et al. 2007). However, one of our goals has been to provide an inventory of the overall assemblage of insects occupying trap nests at the MWC. Therefore, we here report on the abundance, species composition, and (for some species) offspring sex ratios of nest-provisioning species and their insect natural enemies. To our knowledge, our study is the first such survey reported for the MWC and one of relatively few done in the northeastern US. We compare our results to earlier surveys done in eastern and north-central North America (Fye 1965, Jenkins and Matthews 2004, Koerber and Medler 1958, Krombein 1967, Taki et al. 2008a). Materials and Methods The trap nests consisted of 16-cm-deep wood blocks drilled with 15-cm long holes of different diameters, into which we inserted cardboard tubes (Custom Paper Tubes, Inc., Cleveland, OH) with inside diameters of 3.2, 4.3, 5.0, 6.0, 7.0, 8.1, and 9.1 mm to provide potential nest sites for cavitynesting species (Krombein, 1967); hereafter, we use nest size values rounded to the nearest integer. The cardboard tubes were open at both ends, but the inner ends abutted the back wall of the wood blocks. Each set of trap nests consisted of multiple boards containing, in combination, 6–10 tubes of each diameter. Krombein (1967) noted that trap nests were more likely to be occupied when placed at the edges of woods, rather than in “dense, shaded areas”. Therefore, we placed bundles of wood blocks on fence posts or attached them to trees at heights of ≈1.5 m (also following Krombein 1967) on the edges of groups of shrubs and trees, so that the southeast-facing openings of the trap nests were exposed to full sunlight in the morning, but were at least partially shaded in the afternoon. Such placement likely enhances the 2010 K.M. O’Neill and J.F O’Neill 457 ability of the insects to be active earlier in the morning, while protecting nest occupants from intense insolation during the afternoon. In 2001 (21 May) and 2002 (16 May), sets of trap nests were placed at five locations within and near the MNWR, which straddles Seneca, Wayne, and Cayuga counties. Four sets were within the refuge itself: 1) MNWR-1: at the southern edge of the refuge’s “North Spring Pool” (42°58'49.00"N, 76°46'23.62"W); 2) MNWR-2: along the western edge of a meadow at the refuge’s “Overlook” (42°58'29.84"N, 76°46'14.43"W); 3) MNWR-3: along the western edge of a meadow on Lay Road (42°58'12.32"N, 76°46'48.08"W); and 4) MNWR-4: along the northern edge of a meadow 160 m south of MNWR Headquarters (42°57'56.44"N, 76°44'18.46"W). A fifth set, that we refer to as MNWR-5, was placed 2.5 km SE of the refuge at the edge of a forest clearing on private property (42°56'50.26"N, 76°43'1.22"W). Common tree species in vicinity of trap nests included Tilia americana L. (Basswood), Prunus virginiana L. (Chokecherry), Populus deltoides Bartram ex. Marsh (Eastern Cottonwood), Fraxinus pennsylvanica Marsh. (Green Ash), and Acer saccharinum L. (Silver Maple). In 2005 (6 June), 2006 (13 June), and 2007 (21 May), trap nests were placed at ten (2005) or six (2006–2007) locations within the Northern Montezuma Wildlife Management Area, in a part of the area within Cayuga County referred to as “Howland Island”, which is bounded by the Seneca River and the Erie Canal. Habitat on the island contains a mix of marshes, meadows, agricultural fields (some fallow and weedy, some planted with corn), and woodlands with Eastern Cottonwood, Green Ash, Silver Maple, Fagus grandifolia Ehrh. (American Beech), Juglans nigra L. (Black Walnut), Salix nigra Marsh. (Black Willow), Rhamnus cathartica L. (European Buckthorn), Rhus typhina L. (Staghorn Sumac), and Quercus bicolor Willd. (Swamp White Oak). All trap nests were placed within 50 m of two dirt roads on Howland Island referred to on trail maps as Hunter’s Home Road and Wood Duck Loop; the roads are not open to the public, so receive little traffic. Traps were placed in an area bounded by 43°4'40.46"N, 76°42'2.17"W on the west side of Howland Island to 43°5'17.32"N, 76°40’'19.43"W in the center of the island. Three to five times each year, from mid-June to late September, we visited all sets of trap nests, removed nest tubes that had final plugs made by the nest-provisioners, and replaced them with empty tubes, except on the last visit of the year. Nests were kept at room temperature in ventilated plastic bags until mid-November when they were transferred to Montana State University and placed in cold storage (8 °C, 85% relative humidity). All tubes were removed from cold storage in April of the following year and placed individually in glass culture tubes with ventilated lids; a piece of fine-meshed fabric was placed between the lid and tube to help prevent wasps of the genus Melittobia (Eulophidae) from entering or leaving. Still, some nests were parasitized by Melittobia, so any glass tubes containing 458 Northeastern Naturalist Vol. 17, No. 3 Melittobia were immediately placed in a freezer to kill the wasps and prevent them from spreading to other nests; because this also killed surviving offspring of the nest provisioners, these nests were not included in the survey results; fewer than 10% of nests were lost in this way. All nests were checked daily for emergence of the offspring of nest-provisioning bees and wasps, or non-Melittobia parasitoids and predators. Emerging insects were freeze-killed within vials labeled with a nest identification number and date of emergence. After all insects emerged from the 2006 nests, we dissected the nest tubes to identify any adults that did not exit nests, examine contents of cells that did not produce offspring, and when possible, count the number of cells constructed. Insects were identified using published keys and web resources for bees (Droege 2009, Michener et al. 1994, Mitchell 1962) and wasps (Bohart and Kimsey 1982; Bohart and Menke 1963, 1976; Buck et al. 2008; Coville 1982; Sandhouse 1940; Townes 1957; Vincent 1979), and all identifications were checked by one of us (K.M. O’Neill) against specimens in the Cornell University Insect Collection and the Montana Entomology Collection at Montana State University. To examine offspring sex ratios within nests, we used chi-square goodness-of-fit tests (1 d.f. each) to test the hypothesis that sex ratios deviated from the null hypothesis of 1:1. We used chi-square contingency table analyses to compare 1) sex ratios between nests of different diameters and 2) wasp:bee species ratios between sites or studies. All tests conducted had one degree-of-freedom. Results Nest-provisioning wasps and bees within nests Trap-nesting insects and their insect associates emerged from 379 nest tubes. The 347 nests that could be attributed to one or more nest-provisioning species were occupied by 27 species of solitary bees and wasps (Table 1), including 6 apoid wasps (Sphecidae, Crabronidae; 34.3% of nest tubes), 7 vespid wasps (Vespidae: Eumeninae; 38.6%), 2 spider wasps (Pompilidae; 3.2%), and 12 bees (Megachilidae, Colletidae; 25.9%). All of the nest-provisioning species are endemic to North America, with the exception of Megachile rotundata. The seven most common species— Trypoxylon lactitarse (19.3% of nests), Ancistrocerus antilope (17.3%), Hylaeus annulatus (7.8%), Isodontia mexicana (6.3%), Symmorphus canadensis (6.1%), Euodynerus foraminatus (5.8%), and Symmorphus cristatus (5.8%)—occupied nearly 70% of the 347 nests. The seven rarest species were each found in less than 1% of nests. Among species that emerged from at least 5% of nests at a site, Heriades leavitti and Megachile centuncularis were found only at MNWR, while E. foraminatus and S. cristatus were present only on Howland Island. Among rarer species, three Megachile (M. centuncularis, M. mendica, M. pugnata) and Osmia lignaria were collected only at MNWR, 2010 K.M. O’Neill and J.F O’Neill 459 and Ancistrocerus adiabatus, M. quadridens, M. campanulae, and O. pumila only on Howland Island. Because of the different timing and intensity of sampling, few statistical comparisons can be made between the results of the surveys at MNWR and Howland Island, but one difference is notable: the ratio of wasp to bee nests was 5.7:1 at Howland Island (n = 255), but just 0.9:1 at MNWR (n = 99; chi-square contingency table analysis: χ2 = 53.24, d.f. = 1, P < 0.0001). Most nest provisioners used a range of nest diameters spanning no more than three of the seven tunnel diameters provided (Table 1). All eight H. leavitti nests, for example, were in 3-mm tubes (Jensen et al. 2007). In contrast, three species used a range of four (Dipogon sayi) or five (Ancistrocerus antilope, E. foraminatus) of the seven sizes available (Table 1). The most anomalous nest was in a 9-mm tube that had four cells of T. lactitarse cells along with two of Hylaeus annulatus, which otherwise used only 3–4 mm tubes. The maximum number of cells within individual nests was ≥10 in seven species (Table 1). The greatest number of cells in any one nest was 21, found in a 3-mm tube that had 19 H. annulatus cells and 2 Passaloecus cuspidatus cells. Our best quantitative estimate of the number of cells per nest came from T. lactitarse nests dissected in 2006, which had a mean ± standard error of 4.8 ± 0.3 cells (range = 3–8, n = 27). Offspring of two different nest-provisioning species emerged from 14 nests (nest diameter in mm in parentheses): I. mexicana / T. lactitarse (8), I. mexicana / M. pugnata (8), P. cuspidatus / S. canadensis (4), P. cuspidatus / Hylaeus annulatus (4), Trypoxylon collinum / Heriades carinatus (5), Trypoxylon frigidum / Hylaeus annulatus (3), T. lactitarse / A. antilope (8), T. lactitarse / Hylaeus annulatus (9), A. antilope / E. foraminatus (4), Heriades carinatus / Heriades leavitti (3*), Heriades carinatus / M. campanulae (5), Heriades leavitti / Hylaeus annulatus (3*), M. campanulae / O. pumila (6), and M. centuncularis / M. pugnata (6); the two records marked with an asterisk were previously given in Jensen et al. (2007). During 2003–2004, when we conducted a focal study of I. mexicana at MNWR (O’Neill and O’Neill 2009), 21% of 58 I. mexicana nests at the MNWR-1 site had been originally occupied by T. lactitarse or M. relativa. However, one cannot determine from such cohabitation data whether the interactions between species involved usurpation or whether I. mexicana simply took over nests previously abandoned by the other species. Another case of co-habitation occurred between T. frigidum and Passaloecus (probably P. cuspidatus) at Howland Island, and although no offspring of the latter emerged from the nest, several resin partitions indicate that Passaloecus occupied the nest tube after the Trypoxylon cells were constructed. This particular case illustrates a possible hidden cost to offspring developing in a nest taken over by another species. The single adult offspring of the T. frigidum, as well as an adult Trichrysis doriae (a brood parasite of Trypoxylon; Bohart and Kimsey 1982), were found dead behind a hardened resin partition. Apparently, the offspring of Trypoxylon and 460 Northeastern Naturalist Vol. 17, No. 3 Table 1. Number of nests occupied by cavity-nesting species at the Montezuma Wetlands Complex. Numbers given for each species are frequencies of nests occupied Montezuma National Wildlife Refuge (2001–2002)/Howland Island (2005–2007); sex ratios are for combined data. Sex ratio of Maximum # Nest diameter (mm) emerging offspring of offspring 3 4 5 6 7 8 9 TotalA as % females (n) from single nest Sphecidae Isodontia mexicana (Saussure) - - - - 0/1 4/8 2/7 6/16 42.2 (83) 9 Crabronidae Trypoxylon collinum Smith 0/2 0/1 2/2 - - - - 2/5 62.5 (16) 3 T. frigidum Smith 3/4 0/6 - - - - - 3/10 36.7 (30) 5 T. lactitarse Saussure - - - - 6/5 2/26 1/27 9/58 43.1 (255) 8 Passaloecus cuspidatus Smith 1/0 5/2 - - - - - 6/2 50.0 (26) 6 P. monilicornis Dahlbom 1/0 1/0 - - - - - 2/0 0.0 (4) 3 Vespidae Ancistrocerus adiabatus (Saussure) - - 0/4 - - - - 0/4 42.9 (7) 4 A. antilope (Panzer) - 0/1 2/11 1/6 2/8 0/17 0/12 5/55 36.1 (158) 9 Euodynerus foraminatus (Saussure) - 0/1 0/9 0/2 0/4 0/2 0/2 0/20 61.3 (80) 9 Monobia quadridens (L.) - - - - - - 0/2 0/2 0.0 (3) 2 Symmorphus albomarginatus (Saussure) - 1/0 3/0 0/1 1/1 - - 5/2 61.9 (21) 4 S. canadensis (Saussure) 7/9 0/4 - 0/1 - - - 7/14 47.1 (85) 11 S. cristatus (Saussure) 0/8 0/9 0/3 - - - - 0/20 46.0 (78) 10 2010 K.M. O’Neill and J.F O’Neill 461 Table 1, continued. Sex ratio of Maximum # Nest diameter (mm) emerging offspring of offspring 3 4 5 6 7 8 9 TotalA as % females (n) from single nest Pompilidae Dipogon sayi sayi Banks - 0/1 0/2 1/0 1/2 0/3 - 2/8 43.5 (23) 6 Auplopus mellipes (Say) - - - - - - 0/1 0/1 0.0 (1) Megachilidae Heriades carinatus Cresson 3/6 1/2 0/4 - - - - 4/12 46.2 (39) 10 H. leavitti Crawford 8/0 - - - - - - 8/0 41.9 (43) 14 Hoplitis spoliata (Provancher) - - 1/0 - - - - 1/0 0.4 (5) 5 Megachile campanulae Robertson - - 0/1 0/3 - 0/1 - 0/5 0.6 (20) 9 M. centuncularis (L.) - - - 2/0 5/0 - - 7/0 86.4 (44) 13 M. mendica Cresson - - - - 2/0 - - 2/0 88.9 (18) 10 M. pugnata Say - - - 1/0 - 3/0 - 4/0 0.0 (6) 2 M. relativa Cresson - - - - 2/7 1/1 - 3/8 48.0 (50) 9 M. rotundata F. - 2/0 - - - - - 2/0 57.1 (7) 6 Osmia lignaria Say - - - 2/0 - - - 2/0 0.0 (10) 6 O. pumila Cresson - - 0/1 0/4 - - - 0/5 69.6 (23) 7 Colletidae Hylaeus annulatus (L.) 18/3 1/4 - - - - 0/1 19/8 54.9 (175) 19 AThe total number of nests from which at least one species emerged was 347, but 14 nests contained offspring of two species, so the grand total in this column is 354. 462 Northeastern Naturalist Vol. 17, No. 3 Trichrysis were unable to break through the resin barrier created by the Passaloecus female. Offspring sex ratios Among the seven species that occupied at least 20 nests (Table 1), two displayed overall male-biased sex ratios among offspring (A. antilope: χ2 = 12.25, P < 0.001; T. lactitarse: χ2 = 4.80, P = 0.03), while one produced excess female offspring (E. foraminatus: χ2 = 4.05, P = 0.04). In four species, there was no sex-ratio bias: I. mexicana (χ2 = 2.04, P = 0.15), S. canadensis (χ2 = 0.29, P = 0.59), S. cristatus (χ2 = 0.46, P = 0.50), and H. annulatus (χ2 = 1.65, P = 0.20). For some species, sex ratios varied among nests of different diameter. For A. antilope, 4–7-mm nests produced 17% females (n = 81), while 8–9-mm nests produced 54% females (n = 72) (chi-square contingency table analysis: χ2 = 22.9, d.f. = 1, P < 0.001). In T. lactitarse, 7–8-mm nests produced 28% females (n = 145), while 9-mm nests produced 63% females (n = 110; χ2 = 30.3, d.f. = 1, P < 0.001). Such differences also occurred in species that displayed no overall sex-ratio bias. For H. annulatus, 3-mm nests produced 48% females (n = 146), while 4-mm nests produced 93% females (n = 27; χ2 = 18.3, P < 0.001). In I. mexicana nests, 7–8-mm nests produced 30% females (n = 50), while 9-mm nests produced 61% females (n = 33; χ2 = 7.64, P = 0.006). However, for E. foraminatus, we found no difference in sex ratios between 4–6-mm (58% females, n = 40) and 7–9-mm nests (65% females, n = 40) (χ2 = 0.21, P = 0.65). Similarly, no differences were found when comparing 3-mm nests to larger nests in either S. canadensis (χ2 = 0.19, P = 0.66) or S. cristatus (χ2 = 0.08, P = 0.78). Natural enemies Along with the progeny of nest-provisioners, a diverse set of 102 other insects from three orders emerged from nests (Table 2). All but one of these insects are parasitoids, brood parasites, or predators of nest-provisioning bees and wasps; the exception was Perilampus hyalinus, a known parasitoid of sarcophagid flies. Discussion Several researchers in the past 50 years have also conducted surveys of trap-nesting bees and wasps in eastern and north-central North America (Table 3). In all of the cited studies, trap nests were placed in multiple locations, although the surveys varied in duration and in the types of microhabitats in which nests were placed. Another major difference was in the range of trap-nest diameters provided. A few studies provided no trap nests with tunnel diameters <6 mm, while Krombein (1967) set out 12.7-mm diameter nests. The two studies conducted closest to our site were those of Krombein (1967) and Taki et al. (2008a). At Derby, NY, 180 km SSW of the MNWR, 2010 K.M. O’Neill and J.F O’Neill 463 Krombein placed trap nests on and near human structures and along creek banks. Among 346 trap nests occupied, the ≈25:1 ratio of wasp to bee nests was even more extreme than we observed at Howland Island. Among the wasps, >69% were eumenines, including A. antilope (32%) and two species of Ancistrocerus (≈20% combined) not found at MWC. All three eastern North American Symmorphus were also present, as well as E. foraminatus. Among the apoid wasps, P. cuspidatus, T. collinum, and T. frigidum were recorded at both Derby and MWC, but I. mexicana was absent at Derby and T. lactitarse was present in a smaller percentage (8%) than at the MWC (19%). Four of six bees at Derby were also found at the MWC, but the four did not include the most common bee at MWC, H. annulatus. Because Krombein provided one size class of trap nests (12.7 mm) of greater diameter than the largest in our study (9.1 mm), it is possible that we could have missed or under-sampled some species that he found. However, the only two common species using 12.7-mm tubes at Derby, A. antilope and T. lactitarse, were the two most common wasps at MWC. On the other hand, we may have underestimated the abundance of M. quadridens, whose nests in Krombein’s (1967) studies were “almost all” in 12.7-mm tubes (though never at Derby, NY). Taki et al.’s (2008a) study in southern Ontario was conducted 310 km W of the MWC, also within a mixture of forested and agricultural lands. The results, however, contrast strongly with ours, perhaps partly because their trap-nest sites and nest-box orientations were chosen randomly as part of their particular experimental design, whereas our traps were placed specifi- cally at the edges of open areas (e.g., roadways or forest clearings) and all faced southeast. The Canadian study also included a test of the effect of covering some sets of trap nests with burlap covers, but we consider their combined data set here. The greatest difference between the two sites is that no bees occupied nests in Ontario, suggesting major habitat differences; nests in Ontario were also monitored throughout the summer, so any differences between the studies are not likely to be related to temporal patterns of sampling. Among the wasps using their trap nests (n = 531), eumenines predominated (84% of nests), with A. antilope being most common (69%). Apoid wasps were rare (three Trypoxylon nests and one I. mexicana). Overall, there are broad similarities between the studies at MWC, Derby, and Ontario, in that 14 of 24 species at Derby and 8 of 12 species at the Canadian site also occurred at MWC. The differences among the sites are likely related to site-selection methods, as well as historical land-use patterns and local site conditions, which have been shown to be important (Barthell et al. 1998, Fye 1972, Gathmann et al. 1994, Steffan-Dewenter 2003, Taki et al. 2008b, Tscharnke et al. 2003). At a smaller spatial scale, we observed variation in species assemblages among the sampling locations in our study. At MNWR, for example, the ratio of wasp to bee nests was 0.06:1 for the combined data set for MNWR-1 and MNWR-3, but reversed to 3.9:1 at MNWR-5 (χ2 = 39.9, d.f. = 1, P < 0.0001). Similarly, at Howland Island in 464 Northeastern Naturalist Vol. 17, No. 3 Table 2. Non-nest provisioning insects emerging from trap nests (both sites). Genus abbreviations: A. = Ancistrocerus, I. = Isodontia, T. = Trypoxylon, H. = Hylaeus, S. = Symmorphus, M. = Megachile. Nest Species that Type of # of Number diameters Natural enemy provisioned nest enemyA nests emerged (mm) Published host recordsF Coleoptera Meloidae Nemognatha sp. Megachile sp.B BP 1 1 7 Megachilidae Cleridae Unknown sp. Unknown Pr 1 1 3 cavity-nesting bees Diptera Anthomyiidae Eustalomyia sp. UnknownC BP 1 2 5 Eustalomyia vittipes (Zett.) attacks I. mexicana Sarcophagidae Amobia sp.D A. antilope BP 1 6 8 Vespidae (Eumeninae), Sphecidae, Crabronidae I. mexicana 4 17 8–9 T. lactitarse 2 2 9 Unknown 4 7 4–6 Hymenoptera Ichneumonidae Unknown sp. Unknown Pa 1 2 7 Leucospidae Leucospa affinis Say Megachile sp.B Pa 1 1 7 bees, including Megachile Gasteruptiidae Gasteruption sp. H. annulatus Pa 1 3 3 Gasteruption assectator L. attacks H. annulatus Perilampidae Perilampus hyalinus Say Unknown Pa 1 1 4 Sarcophagidae 2010 K.M. O’Neill and J.F O’Neill 465 Table 2, continued. Nest Species that Type of # of Number diameters Natural enemy provisioned nest enemyA nests emerged (mm) Published host recordsF Chrysididae Chrysis cembricola Krombein S. canadensis BP 1 1 3 Symmorphus canadensis C. coerulans F. Unknown BP 16 16 5–9 Ancistrocerus, Euodynerus, Parancistrocerus, S. cristatus C. nitidula F. A. antilope BP 7 15 5–7, 9 Ancistrocerus, Euodynerus, Symmorphus Unknown 6 9 5–8 Chrysis sp. A. antilope BP 1 1 9 Chrysura pacifica (Say) Osmia sp. BP 1 1 6 Osmia, including O. pumila, Trichrysis carinatus (Say) T. lactitarse BP 4 4 8–9 Trypoxylon, including T. collinum and T. lactitarse Unknown 2 2 4 Trichrysis doriae (Gribodo) T. frigidum BP 1 1 4 Trypoxylon, including T. frigidum and T. collinum Megachilidae Coelioxys moesta Cresson M. centuncularis BP 1 1 7 Megachile, including M. centuncularis M. relativa 1 1 7 Megachile, including M. relativa Sapygidae Sapyga louisi H. leavittiE BP 2 6 3 Heriades carinatus Sapyga sp. O. pumila BP 1 1 6 Sapyga centrata Say attacks O. pumila ABP = brood parasite, Pa = parasitoid, Pr = predator. BLikely one of the species listed in Table 1, but dead adult in nest was not identifiable to species. CThis was clearly a Trypoxylon nest, with mud plugs and remains of spider prey. DThese records count only emerged adult flies; some nests also contained many puparia that may well have belonged to Amobia. EThis record reported earlier in Jensen et al. (2007). FFrom Matthews (1965), Krombein (1967), Krombein et al. (1979), and Bohart and Kimsey (1982). 466 Northeastern Naturalist Vol. 17, No. 3 Table 3. Comparison of trap-nest surveys conducted in eastern and northern United States, listed in order from north to south. Duration # of North of survey nests Diameters # of Bee:wasp Site latitude (years) occupied placed (mm)F species nest ratio Most common species (% of all nests) Western OntarioA 49°20' 3 202 6, 8 9 - WisconsinB 42°30'– 46°50' 1 778 6, 8 22 - Euodynerus foraminatus (21), Dipogon sayi sayi (18), Ancistrocerus antilope (18) MWC 42°56'–43°5' 5 347 3, 4, 5, 6, 7, 8, 9 27 0.34:1 Trypoxylon lactitarse (19), A. antilope (17), Isodontia mexicana (6) Southern OntarioC 42°37'–42°48' 1 531 3, 5, 7, 9 12 0:1 A. antilope (68), Auplopus mellipes Say (9), D. sayi (6), Ancistrocerus adiabatus (6) Derby, NYD 42°42' 8 372 3, 5, 10, 13 21 0.04:1 A. antilope (30), Symmorphus cristatus (17), Ancistrocerus catskill (Saussure) (12) Plummers Island, MDD 38°58' 7 762 3, 5, 10, 13 32 0.36:1 T. lactitarse (29), Osmia lignaria (18), T. clavatum Say (10) Kill Devil Hills, NCD 36°00' 3 252 3, 5, 10, 13 21 0.07:1 T. collinum (18), T. clavatum Say (15), Euodynerus megaera (Lepeletier) (8) Georgia and South CarolinaE 33°70'–35°02' 1 255 6, 10, 13 11 0.25:1 E. megaera (36), I. mexicana (19), Megachile frigida Smith (16) Lake Placid, FLD 27°10' 5 780 3, 5, 10, 13 29 0.1:1 E. foraminatus (31), Pachodynerus erynnis (Lepeletier) (11), M. quadridens (10) AFye 1965 (paper gives results for wasps only). BKoerber and Medler 1958 (paper provides individual abundances for most abundant of 22 species). CTaki et al. 2008a. DKrombein 1967. EJenkins and Matthews 2004. FValues rounded to nearest 1 mm. 2010 K.M. O’Neill and J.F O’Neill 467 2007, all 27 completed nests at sites 1 and 2 were provisioned by eumenine wasps, whereas 12 of 23 nests at site 3 were occupied by bees (χ2 = 27.0, d.f. = 1, P < 0.0001), and only 2 by eumenines. Thus, characterizations of overall cavity-nester assemblages within an area are improved by placing multiple sets of trap nests in different locations. In Wisconsin, Koerber and Medler (1958) sampled a large array of sites with latitudes overlapping those of MWC; the three most common nest-provisioning species at their sites were also found at ours (Table 3). However, although the ratio of bee to wasp nests remains low as one moves farther south along the eastern seaboard, the list of the most common trap-nesters diverges increasingly from that for MWC. At Plummer’s Island, MD, T. lactitarse was also the most common wasp, but T. clavatum (absent from MWC) ranked third overall, and O. lignaria (rare at MWC) was the most common bee (Krombein 1967). In North Carolina, T. collinum replaced T. lactitarse as the most common wasp. In disturbed habitats in Georgia, four of the five most common species (the bee M. frigida, and the wasps E. megaera, S. plenoculoides, and A. campestris) occupied 67% of the nests, but were absent from our sites (Jenkins and Matthews 2004). Among the three most common species at MWC, two were absent (A. antilope, H. annulatus) and one (T. lactitarse) was rare (less than 2% of nests) in Georgia. The absence of such genera as Hylaeus from the Georgia data (even though it has been collected in that state; Mitchell 1962) is not surprising because the researchers were not conducting a broad survey, so they did not provide tunnels of less than 6 mm diameter. Only I. mexicana was common at both MWC and in Georgia; I. mexicana is endemic to much of North America, and has even spread recently to southern Europe (Pagliano et al. 2001) and the Midway Atoll in the central Pacific (Nishida and Beardsley 2002). The most distant comparison to be made with our survey is that with Krombein’s (1967) study from Florida. There, although E. foraminatus was the most common trap-nester by far, the Florida population is E. foraminatus apopkensis (Robertson), whereas the NY wasps are E. foraminatus foraminatus (Saussure). Of the two species ranked next in Florida, Pachodyneris erynnis is of a genus unrepresented at MWC (or any of the other sites listed in Table 3), and M. quadridens was extremely rare (just two nests at MWC). Two other wasp genera from Florida, Podium (one species) and Stenodynerus (four), were also unrepresented at MWC, although two nests of Stenodynerus pedestris (Saussure) were found at Derby. Offspring sex ratios Brood sex ratios of solitary bees and wasps are readily manipulated by egg-laying females because of their haplodiploid sex determination system, in which fertilized eggs produce females and unfertilized eggs males. Sex ratios are often biased towards one sex (most often males) in solitary nestprovisioning species, and variable among sites and between nests within 468 Northeastern Naturalist Vol. 17, No. 3 sites (Krombein 1967). The sex of the offspring in any given brood cell is related to multiple factors, including (among others) 1) its position within a nest (because males emerge before females, they must be in the outermost cells), 2) the amount of food that can be provided (females are larger, so require more food), and 3) the diameter of the nest (the largest females may not fit within the smallest tunnels); see O’Neill (2001) for review of factors influencing the evolution of sex ratios in solitary wasps. For the common species we observed at MWC, emergence sex ratios are typically either male-biased or unbiased, but they often vary among studies. Male-biased sex ratios were found for A. antilope at Derby, NY (χ2 = 27.4, P < 0.001; Krombein 1967); E. foraminatus at Derby, NY (χ2 = 14.5, P < 0.001; Krombein 1967); S. canadensis and S. cristatus in Ontario (Longair 1981); and T. lactitarse at Derby (χ2 = 18.8, P < 0.001; Krombein 1967) and in Wisconsin (χ2 = 11.6, P < 0.001; Medler 1967). Sex ratios statistically indistinguishable from unity (at α = 0.05) have been reported for H. annulatus in Ontario (χ2 = 3.6, d.f. = 1, P = 0.06; Fye 1965), A. antilope in Ontario (Longair 1981), E. foraminatus in Ontario (Longair 1981), S. canadensis (χ2 = 0.2, P = 0.65) and S. cristatus (χ2 = 0.7, P = 0.40) at Derby, NY (Krombein 1967), I mexicana at MWC in a different study conducted from 2004–2005 (χ2 = 2.2, P = 0.14; O’Neill and O’Neill 2009), and I. mexicana in Montana (χ2 = 0.7, P = 0.40; O’Neill and O’Neill 2003); with the exception of those by Longair (1981), all analyses above are our own, based on the published data. Thus, some previously reported sex ratios for H. annulatus, A. antilope, S. cristatus, and E. foraminatus differ from those that we observed. For S. cristatus, this may be due to the relatively small sample sizes reported. However, the difference between studies of E. foraminatus at Derby and MWC may be related to the sizes of tunnels used by wasps at the two sites: all nests at Derby were within 4.8–6.4-mm tunnels (even though larger diameters were available) and produced 24% females, whereas 40% of the nests at MWC of were in 7–9-mm tunnels, where 65% of offspring were females. However, unbiased sex ratios for H. annulatus were found both in Ontario (Fye 1965), where females nested in 6.4–8.0-mm tunnels, and at MWC, where most nests were within 3–4-mm tubes. Comparisons of sex ratios among populations are complicated by the fact that sex ratios may vary not only with the particular frequency distribution of nest sizes made available, but with the length of the tunnels provided, the generation sampled (in bivoltine species), and the quality and quantity of resources available to provisioning females (Danks 1983, Longair 1981, O’Neill 2001). Natural enemies Our observations on natural enemies emerging from nests confirm many previous host records (Bohart and Kimsey 1982, Krombein 1967, Krombein et al. 1979). The most common group of natural enemies were cuckoo wasps (Chrysididae), with 50 individuals of 7 species emerging 2010 K.M. O’Neill and J.F O’Neill 469 from 39 nests. No host offspring emerged from 24 of the 39 nests, so we cannot always draw definite conclusions about host associations. Particularly striking is the fact that Chrysis coerulans never emerged from nests that also produced host offspring; however, all of those nests contained mud plugs and partitions typical of eumenine nests, and all previous host records for C. coerulans are eumenines (Bohart and Kimsey 1982). For Chrysis nitidula, the case is stronger that its hosts were A. antilope, because that wasp emerged from seven of the nests that also produced C. nitidula; in four nests, C. nitidula attacked multiple (2–5) cells. The second most common group of natural enemies were flies of the genus Amobia, which are well-known brood parasites of cavity-nesting apoid wasps (O’Neill 2001). Krombein (1967) and Taki et al. (2008a) also found C. coerulans, C. nitidula, and Amobia to be the most common natural enemies in trap nests. Natural enemies emerged from just 7 of 85 nests that produced bees, but these represented a diverse array of brood parasites (Meloidae, Megachilidae, and Saygidae) and parasitoids (Leucospidae). Conclusions Trap nests placed at the MWC from 2001–2007 attracted a diverse array of solitary nest-provisioning species and their natural enemies. Overall, wasps using the trap nests are known to take a diverse set of prey, including spiders (Trypoxylon, Auplopus, Dipogon), crickets and katydids (Isodontia), aphids (Passaloecus), moth caterpillars (Ancistrocerus, Euodynerus, Monobia), chrysomelid beetle larvae that feed externally on leaves (Symmorphus albomarginatus, S. cristatus), and leaf-mining caterpillars and beetle larvae (S. canadensis) (Krombein 1967, O’Neill 2001). Based on published flower-visitation records and pollen records, bees of the genera emerging from the trap nests may all be polylectic (Krombein et al. 1979, Matteson et al. 2008). The composition of the assemblage of nest-provisioning species was generally similar to those from studies done at similar latitudes, but differed increasingly from those documented in other surveys as one moves further south along the east coast of North America. Some of the variation between studies may be due to differences in methodology (e.g., sizes of nests made available and sampling intensity). Thus, comparisons among existing studies cannot replace those that could be made with simultaneous surveys undertaken along a latitudinal gradient using standardized trap-nesting and site-selection methods, but they do suggest that such studies would likely reveal clear geographic trends in the composition of cavity-nester species assemblages. They could also provide a basis for determining the future effects of climate change and habitat disturbance or restoration on the distribution, abundance, and diversity of trap nesters and their natural enemies. Overall, it is clear from this and previous studies that the use of multiple trap-nest diameters is important if one’s goal is a full assessment of the species composition of an assemblage and the brood sex ratios of a population. 470 Northeastern Naturalist Vol. 17, No. 3 Acknowledgments We thank Tracy Gingrich of the Montezuma National Wildlife Refuge and Dave O’Dell of the Northern Montezuma Wildlife Management Area for help in obtaining research permits and locating research sites. Susan Stubbs provided access to her property near the Montezuma National Wildlife Refuge. The following provided help in identifying specific taxa: Richard S. Miller (Heriades, Hylaeus, Leucospa, Perilampus, Sapyga), James Pitts (Pompilidae), and Bryan Danforth (Osmia). Jessica Fultz, Richard Miller, Megan O’Neill, Ruth O’Neill, and April Pearce assisted with field work and monitoring insect emergence. James Liebherr and Richard Hoebeke gave us access to the Cornell University Insect Collection. 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