N11 2018 Northeastern Naturalist Notes Vol. 25, No. X J. Alcock The Mating Behavior of Rhamphomyia pectinata (Empididae: Diptera) with Notes on Other Members of the Genus Found at the Same Locale in Northern Virginia John Alcock* Abstract - The previously unstudied empidid fly Rhamphomyia pectinata is, like many other members of the genus, a sex-role–reversed species with highly ornamented females that gather in swarms to await the arrival of prey-bearing males. Receptive males transfer their nuptial gifts to females before mating with them in the air. Rhamphomyia pectinata is diurnal, with swarming and copulations occurring in the afternoon. Other members of the genus occur at the study site but are crepuscular. Introduction. Empidid flies of the genus Rhamphomyia have been studied by a number of observers who have documented similarities among these flies with respect to their mating behavior (Bussière et al. 2008, Daugeron and Grootaert 2005, Downes 1970, Funk and Tallamy 2000, LeBas et al. 2004, Svensson 1997). Sex-role reversal is common in the genus, with females gathering in groups to await the arrival of males that bear small insectprey gifts. The swarming females, which are typically larger than the males, hover above incoming males that, if receptive, permit the females to drop onto them. Shortly thereafter, the position of the 2 sexes is reversed as the prey is transferred to the female. This behavior is usually followed by copulation in flight. Copulating pairs often occur low, just a few centimeters above the ground, while the pair makes a leisurely flight in tight circles, as the female consumes the nuptial gift she has received from her partner. Consistent with the sex-role reversals commonly seen in this genus, the females are generally the more highly ornamented sex with 1 or more pairs of legs enlarged with pennate setae, and in certain species, with widened and infuscated wings (Cumming 1994). In some, but far from all species, females also can inflate their abdomens to make their bodies appear much larger (Wagner 2003). Field-site Description and Methods. There are a large number of species in the genus; many have remained unnamed, and only a few have been both named and studied. One named species, R. pectinata Loew, is among the unstudied group. This brief report is designed to provide an account of the interactions between the sexes of this species at a site near Marshall, VA, where I observed the flies in an opening with low, weedy vegetation covering the ground in a farm woodlot (Fig. 1). The site is located at 38°52'26.29''N, 77°54'29.88''W. I have sent voucher specimens to the National Collection of Insects, where B. Sinclair and J. Cumming (Ottawa Research and Development Center, Ottawa, ON, Canada) stored them after providing identifications of the flies and a small number of prey taken from copulating pairs of the empidids. The study began on 25 May 2017 at about 1330 EDT, when I observed empidids flying rapidly back and forth 1–2 m above the ground. Fly activity ended when it began to rain at ~1500 EDT. On 26, 27, and 29 May, I observed a few additional flies at the site between 1400 and 1600 EDT. The failure of the flies to appear there at various times during the afternoon on 30 May 2017 marked the end of the study. Results. The flies that flew solitarily or formed small swarms were females with ornamented legs. On 26 May, between 1500 and 1615 EDT, I used an insect net to capture a total *School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501; j.alcock@asu.edu. Manuscript Editor: Joshua Ness Notes of the Northeastern Naturalist, Issue 25/2, 2018 2018 Northeastern Naturalist Notes Vol. 25, No. X N12 J. Alcock of 8 solitary individuals, all of which were females. When males arrived and positioned themselves underneath a rapidly moving female, the female slowed her flight and began to hover; the pair descended toward the ground with the female above the male. When the female dropped onto the back of the male, the pair ascended and disappeared. However, at least 3 copulating pairs appeared in depressions among the weeds where they circled slowly while the female ate the nuptial gift she had received from her partner. Three prey taken from these mating pairs were identified as a mayfly (Ephemeroptera), a bibionid fly in the genus Dilophus, and a small empidid fly ( Rhamphomyia sp. (= Calorhamphomyia sp.). Discussion. The behavior of R. pectinata is similar to that of other members of the genus, as noted in the introduction. Although this species belongs to the group of noninflatable females, the females do have heavily ornamented legs as does the female of an undescribed species of a non-inflating Rhamphomyia that has been studied on the same farm (Alcock 2016), as well as the previously studied inflating R. longicauda Loew (Long-tailed Dance Fly) (Bussière et al. 2008, Funk and Tallamy 2000), which also occurs in the area (see below). However, these latter 2 species are crepuscular, whereas R. pectinata is diurnal with a flight period in the mid-afternoon (Alcock 2016, Funk and Tallamy 2000). As is true for many other members of the genus, males supply females with very small prey belonging to a wide range of insect taxa. As Cumming (1994) has suggested, male nuptial gifts may be the only source of nutrition for females, which has resulted in sexual selection via male choice on females (leading, for example, to the female’s ornamented legs and/or modified wings). Why some species have also evolved the ability to inflate their abdomens is matter of continuing uncertainty. Funk and Tallamy (2000) have presented evidence in favor of the hypothesis that abdominal inflation is a deceptive adaptation of females designed to increase their apparent size and fertility, thus making the females more Figure 1. The clearing in a northern Virginian woodlot where the empidid fly Rhamphomyia pectinata formed its small female swarms in May 2017. N13 2018 Northeastern Naturalist Notes Vol. 25, No. X J. Alcock attractive to potential gift-giving mates. One would think, therefore, that larger females would be more attractive to males; but Wheeler et al. (2012) found no indication that this was true, making the deception hypothesis problematic. The behavior of Rhamphomyia sp. I observed the undescribed species of Rhamphomyia in June of 2015 (Alcock 2016) and again in 2017 at the same location (38°87'08.88''N and 77°90'33.75''W), where it flew in large, primarily female swarms in a woodland near a small stream and above a nearby hayfield, both in the early morning close to sunrise and also in the evening around sundown. I first saw the flies on 1 June, but I made more careful observations on several days in mid-June. That the fly in 2017 was the same (unnamed) species that I observed in 2015 was confirmed by B. Sinclair, who examined a series of specimens taken in 2017. The prey provided by males to their mates were primarily fungus gnats (Keroplatidae); 5 of the 8 copulating females collected fed on these gnats, 2 females consumed small craneflies in the family Limoniidae, and 1 ate a mycetophilid, another family of small flies. The Acer sp. (maple) tree that was a primary focus of swarming females continued to be an important focal point for the flies. Table 1 compares the number of individuals photographed high in the tree against the sky during the swarming period in 2015 and 2017 on from 12–14 June and on June 18. The data collected in 2017 confirmed that the empidids flew in both the early morning and evening, with the greatest number of swarming individuals appearing in the earliest morning and the latest evening samples. The flies, however, were also present at 2 other locations in the woodland in 2017, such that groups often formed around the end of a branch of a Nyssa sylvatica Marshall (Blackgum) tree growing out at right angles to the trunk about 4–5 m above the ground. The tree was only a few meters away from the maple, with its much higher swarm. Lower still, during mornings and evenings, I observed a vertical swarm extending 1–3 m in height a short distance from the Blackgum tree. There was open sky above the swarming flies at all 3 sites. The behavior of Rhamphomyia longicauda. The large aggregation of females of this previously well-studied species (Funk and Tallamy 2000, Newkirk 1970) had disappeared from the nearby woodland by mid-June of 2015 (Alcock 2016), leading to the conclusion that the flight period for R. longicauda ended before the peak period of swarming by the unnamed Rhamphomyia; thus, it was surprising to collect females of R. longicauda (identified by B. Sinclair) beneath the maple tree at the same time in 2017 in which the unnamed species of Rhamphomyia was present. Copulating pairs of this unnamed species and females and at least 1 male R. longicauda both occurred close to the ground in the narrow, leafcovered depression formed by runoff that ran through the weedy understory of the woodland down to the small stream. I collected these specimens in mid-June, when I observed females Table 1. Counts of flies made in mid-June 2015 and 2017 (in parentheses) of the undescribed species of Rhamphomyia at 30-min intervals (EDT) based on photographs taken of the swarm at the maple tree top (it was impossible to take photographs after 20:45 due to insufficient light). A hyphen indicates that no data were collected at that time. Time 12 June 13 June 14 June 18 June 05:45 108 (67) 110 (99) 78 (81) - (40) 06:15 146 (61) 82 (52) 69 (21) - (40) 06:45 70 (22) 21 (16) 52 (3) - (9) 07:15 9 (4) 5 (0) 22 (0) - (13) 20:15 - (32) 16 (28) 21 (13) 5 (3) 20:45 - (63) 37 (28) 67 (45) 17 (8) 2018 Northeastern Naturalist Notes Vol. 25, No. X N14 J. Alcock of R. longicauda in the early morning and evening, as late as 18 June 2017. Studies of this species from more northerly regions have produced records of the fly occurring into July (Funk and Tallamy 2000, Wheeler et al. 2012). Acknowledgments. Once again, the help of Jeffrey Cumming and Bradley Sinclair of the Canadian National Collection of Insects, K.W. Neatby Building, Ottawa, ON, Canada was invaluable both in terms of identifying the empidids and their prey as well as vis-à-vis evaluating the manuscript. Literature Cited Alcock, J. 2016. The mating behavior of an undescribed species of Rhamphomyia (Diptera: Empididae). Journal of Insect Behavior 29:153–161 Bussière, L.F., D.T. Gwynne, and R. Brooks. 2008. Contrasting sexual selection on males and females in a role-reversed swarming dance-fly, Rhamphomyia longicauda Loew (Diptera: Empididae). Journal of Evolutionary Biology 21:1683–1691. Cumming, J.M. 1994. Sexual selection and the evolution of dance-fly mating systems (Diptera: Empididae; Empidinae). Canadian Entomologist 126:907–920. Daugeron, C., and P. Grootaert. 2005. Atypical mating behavior in the empidine dance fly Rhamphomyia (Lundstroemiella) magellensis (Diptera: Empididae: Empidinae). Belgian Journal of Zoology 135:97–99. Downes, J.A. 1970. The feeding and mating behavior of the specialized Empidinae (Diptera): Observations on 4 species of Rhamphomyia in the high arctic and a general discussion. Canadian Entomologist 102:769–791. Funk, D.H., and D.W. Tallamy. 2000. Courtship role reversal and deceptive signals in the Long-tailed Dance Fly, Rhamphomyia longicauda. Animal Behavior 59:411–421. LeBas, N.R., L.R. Hockham, and M.G. Ritchie. 2004. Sexual selection in the gift-giving dance fly, Rhamphomyia sulcata, favors small males carrying small gifts. Evolution 58:1763–1772. Newkirk, M.R. 1970. Biology of Long-tailed Dance Fly, Rhamphomyia longicauda (Diptera: Empididae): A new look at swarming. Annals of the Entomological Society of America 63:1407–1412. Svensson, B.G. 1997. Swarming behavior, sexual dimorphism, and female reproductive status in the sex-role–reversed dance fly species Rhamphomyia marginata. Journal of Insect Behavior 10:783–804. Wagner, R. 2003. Remarkable abdominal appendages of female Empididae and male Dolichopodidae (Diptera: Empidoidea). Entomologia Generalis 26:253–258. Wheeler, J., D.T. Gwynne, and L.F. Bussière. 2012. Stabilizing sexual selection for female ornaments in a dance fly. Journal of Evolutionary Biology 25:1233–1242.