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Pre-copulatory courtship behavior in a solitary bee, Nomia triangulifera Vachal (Hymenoptera: Halictidae) Wt Wcislo, Rl Minckley, Hc Spangler To cite this version: Wt Wcislo, Rl Minckley, Hc Spangler. Pre-copulatory courtship behavior in a solitary bee, Nomia triangulifera Vachal (Hymenoptera: Halictidae). Apidologie, Springer Verlag, 1992, 23 (5), pp.431-442. hal-00891033 HAL Id: hal-00891033 https://hal.archives-ouvertes.fr/hal-00891033 Submitted on 1 Jan 1992 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Original article Pre-copulatory courtship behavior in a solitary bee, Nomia triangulifera Vachal (Hymenoptera: Halictidae) WT Wcislo RL Minckley HC Spangler 1 University of Kansas, Snow Entomological Museum, Department of Entomology, Lawrence, KS 66045-2119; 2 USDA-ARS Carl Hayden Bee Research Center, 2000 E Allen Rd, Tucson, AZ 85719, USA (Received 27 November 1991; accepted 19 May 1992) Summary — Complex courtship behavior occurs both before and during mating of a solitary bee, Nomia triangulifera. Males begin emerging before females, and patrol over the emergence site, al- though some males also fly near sunflower plants, the exclusive food source of the females. The siz- es of males patrolling at these two locations, and those collected while mating were not significantly different. Courtship behavior involves use of the fore- and mid-legs, the metasoma (abdomen), an- tennae, and the indirect flight muscles to produce loud, audible buzzes. The hind legs have expand- ed tibiae which are used for clasping the female. Females rarely mated more than once when held in cages. Receptive females usually lacked sperm in their spermathecae, while unreceptive females of- ten had sperm. Nomia triangulifera / Halictidae / mating behavior / sexual selection INTRODUCTION (eg Darwin, 1871; Richards, 1927; Alcock and Gwynne, 1991; West-Eberhard, Many features of a male’s behavior and 1984). Alternatively, species-specific behavior functions in contexts of morphology are assumed to function to in- courtship isolation or mate duce a female to initiate copulation, and reproductive recognition then stimulate her to continue reproduc- (Verrell, 1988). tive behavior (eg sperm transport, ovula- Most studies to date have reported little tion), thereby increasing the probability or no pre-copulatory courtship behavior that the copulating male will fertilize her among bees (eg Batra, 1966; Barrows, ova (Eberhard, 1985). Such behavior is 1975; Alcock et al, 1978; Triplett and Git- believed to underlie the evolutionary pro- tins, 1988; Eberhard, 1991). Nomia (Epi- cess of sexual selection by female choice nomia) triangulifera Vachal, reported on * Present address: WT Wcislo, Cornell University, Dept of Entomology, Ithaca, NY 14853, USA. here, seems unusual because of its ex- Mating pairs were picked up and quickly placed tremely complex pre-copulatory courtship on a platform set up in front of the camera. Ap- 7 h were made behavior, combined with structural modifi- proximately of audio recordings a Uher 4000 reel-to-reel tape recorder cations. The Nomia using genus (Hymenoptera: (tape speed = 19 cm/s), with a standard micro- most re- Halictidae) occurs throughout phone (which often served as the platform for gions of the world, and in the New World is filming). For analyses, recordings were played represented by 20 species in four subgen- through a Krohn-Hite mode 3550 filter (LP == a Elemetrics DSP era (Moure and Hurd, 1987)*. Most male 575 Hz) to Kay Sonagraph Nomia have highly modified hind legs, (Model 5500). metasomal sterna and genitalia, which To examine size-related patterns of mating provide species-specific taxonomic char- behavior, we measured the sizes (inter-tegular distances) of females and their male partners acters Michener, 1965; (eg Cross, 1958; (N = 20 males and 20 females), males patrolling The functions of Ribble, 1965). biological at the emergence/nesting site (N = 44), and these secondary sexual characters are un- males patrolling at sunflowers (N = 51), using a known, and comparative studies of the Wild microscope with an ocular micrometer mating biology of this group promise to illu- (magnification = 10X). Some males (N = 21) minate their function. This report, together were dried to a constant weight at 50 °C (Ther- molyne Oven-Incubator), and weighed on a with observations on this species previous Fisher electronic balance to the nearest 0.001 g; and from another locality (Cross Bohart, for these males the lengths at the longest dis- 1960), may provide an example of intra- tance of the inner face of the expanded hind tib- specific divergence in courtship behavior. iae were also measured. The receptivity of females in a cage was studied as follows (after O’Neill and Bjostad, MATERIALS AND METHODS 1987). After being "courted", females exhibited obvious behaviors indicating their sexual recep- tivity: receptive females elevated their metaso- The mating behaviour of Nomia triangulifera ma slightly, and unreceptive females curled the was studied at large aggregations of nests at a metasoma under their body, and sometimes farm on a floodplain along the south bank of the also bit at the males’ legs. Receptivity status of Kansas River between Eudora and Lawrence females with otherwise unknown sexual histo- (Douglas County), Kansas (38 °57’ 30" N, 95°7’ ries was classified as follows: "receptive to 1 st 30" W). Bees have been nesting at this site at male and mated" (= a female copulated with the least since 1972 (Shipe, personal communica- first introduced male) (N = 34); "unreceptive" tion). (= a female refused to mate with the first male) = and to 1 st male and Courtship and mating behavior were studied (N 18); "receptive separ- ated before a female was receptive to by direct observation of > 200 mating pairs. mating" (= the first male, but the was before Copulating bees were largely unresponsive to pair separated = Females from these nearby movements, could be approached within intromission) (N 26). classes were introduced to 3-5 one cm (a 10X hand-lens was sometimes individually males in either a 16 x 12 x 12 cm net-covered used), and mating pairs could even be picked or a 1 x 0.5 x 1 m enclosure up. Mating was either: i) video-taped (3.5 h) us- fish-breeding cage, to ascertain re- ing a Panasonic videocamera with close-up lens (an emergence trap) subsequent and tripod (in 1987 and 1988); or ii) filmed (4 h) ceptivity. with a Paillard Bolex 16-mm film camera with an Mating pairs were observed in the field, and Yvar 150-mm macro-lens and tripod (in 1986). females were categorized as "receptive but un- * Nomia triangulifera is presently placed in the subgenus N (Epinomia). In a forthcoming key, Michen- er et al (in preparation) recognize the genus Dieunomia for N (Epinomia) and N (Dieunomia), and the genus Nomia for N (Acunomia) and N (Curvinomia). For convenience these subgeneric names are retained in the Discussion, although it is likely that some of the groups are artificial. mated" (N = 11) (ie, males were removed before to River Front Park, Lawrence, and at a intromission), or "unreceptive" (N = 14). Fe- site 5 miles north-west of Lawrence (de- males were placed in vials containing insect pre- scribed in Cross and Bohart, 1960). At servative (Kahle’s solution), and were later dis- both sites behavior was sected and examined for presence of sperm courtship qualita- cells in the spermathecae. tively similar to behavior described below Statistical tests were from Sokal and Rohlf (Wcislo, unpublished observations). (1981), or calculated using Statview on a Mack- Most of our observations were of mating intosh computer. pairs on the ground at the emergence site. Voucher specimens of the bees are in the We do not known the relative abundance Snow Entomological Museum, and audio record- of receptive females at the emergence are in the Cornell of Natu- ings University Library sites and at flowers. Males were never ob- ral Sounds; video and audio may be recording served on flowers obtained from the first author. successfully mating (»N = 32 attempted matings), even on plants close to the emergence site. Males over the site RESULTS flying emergence/nesting were not, on average, different in size from males collected at sunflower plants nor N triangulifera was active from mid- to late- from males collected with females in copu- August and into September in eastern la (P > 0.5, with repeated Mann-Whitney U Kansas. The populations were protan- tests). drous, but after several days the emer- The courtship behavior involved mo- gence distributions of the sexes over- tions of the antennae, all three pairs of lapped. On all dates there was a heavily legs, the metasoma and associated sternal male-biased operational sex ratio, both in modifications, and presumably the dorso- a year when the secondary sex ratio was ventral flight muscles. Several details did near equality, and one when it was male not fully agree with the description of court- biased (Wcislo, 1992). Males flew in great ship behavior by Cross and Bohart (1960), numbers over the previous year’s nest site, based upon their limited observations of a which was where receptive females Utah population; descriptions by those au- emerged and where they returned to nest thors are parenthetically italicized for com- if the plant cover was suitably sparse. parison, indicated by "C and B". Otherwise, Males were also abundant on the plant descriptions given below agree with those (Helianthus annuus) from which females by Cross and Bohart (1960).

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