Female Foraging and Intranest Behavior of a Communal Bee, Perdita portalis (Hymenoptera: Andrenidae) BRYAN N. DANFORTH1 Snow Entomological Museum, Department of Entomology, University of Kansas, Lawrence, Kansas 66045 Ann. Entomol. Soc. Am. 84(5): 537-548 (1991) ABSTRACT Female Perdita portalis Timberlake are ground-nesting, partially bivoltine, communal bees that inhabit the deserts and arid grasslands of Arizona, New Mexico, and northern Mexico. From 2 to 29 adult females may share a single nest. Nests are commonly reused from year to year and may become very large, with >200 overwintering prepupae, although some new nests are started each year. By constructing artificial, below-ground observation nests, it was possible to observe the details of cell provisioning and of female (and male) nestmate interactions within the nest. The details of cell construction, pollen collection, pollen ball formation, and oviposition are described. There was no evidence of cooperation among female nestmates or reproductive division of labor, nor was there any indication of intraspecific cleptoparasitism. The behavior of female P. portalis is compared with the behavior of females in other species of Perdita and with what is known of the intranest behavior of other bees. KEY WORDS Insecta, Perdita portalis, nesting behavior, sociality THE GENUS Perdita contains >600 species of small the intranest interactions among nestmates shed to minute bees which are most common in the arid light on theories of social evolution (Lin & Mich- southwestern United States and northern Mexico. ener 1972, Eickwort 1981)? To answer these ques- All species studied to date excavate nests in the tions, one must observe females under seminatural ground, which consist of tunnels leading to cells conditions within nests. This paper outlines the ba- where pollen and nectar are stored for larval de- sic natural history of P. portalis and presents the velopment. Most species are narrowly oligolectic, first observations on intranest behavior of a com- usually restricting pollen collection to a small group munal andrenid bee. of closely related plants. Rozen (1967) and Dan- Although the behavior and morphology of fe- forth (1989) review the published information on male P. portalis are similar to those of many of its Perdita nesting behavior. close relatives, the males of this species are highly Although in many species of Perdita each nest unusual in having two discrete morphs differing in contains just one female (e.g., P. octomaculata (Say) both structure and behavior. One morph is capable [Eickwort 1977]), several species are communal, of flight, is relatively small-headed, and is found with >30 adult females per nest: e.g., P. texana regularly on Sphaeralcea St.-Hilaire (Malvaceae) Cresson (Neff & Danforth 1991); P. opuntiae Cock- flowers, where they mate with foraging females. erell (Bennett & Breed 1985, Custer 1928); P. mel- First discovered by Rozen (1970), the other (de- lea Timberlake (J. G. Rozen, Jr., personal com- rived) morph is strikingly modified, as judged by munication); P. latior Cockerell (J. G. Rozen, Jr., comparison with related bees, possessing a greatly personal communication); P. coreopsidis Cockerell enlarged head, enlarged facial foveae, reduced (Danforth 1989); P. lingualis Cockerell (Michener compound eyes, elongate pointed mandibles, a 1963); and P. portalis. Communal nesting by fe- three-pronged clypeus, and reduced thoracic mus- male Perdita raises a number of questions about culature which renders them flightless and restrict- how females interact behaviorally within nests. Do ed to a life within the natal nest. Unlike most of females cooperate in any aspect of nest construc- its close relatives, which vary continuously in head tion, maintenance, defense, or foraging? Is there size, albeit with strong positive allometry (e.g., P. reproductive division of labor? In communal nests, texana), the males of P. portalis are truly dimor- females have access to the fruits of each others' phic. A detailed description of male intranest be- labor (the pollen and nectar needed for larval de- havior and comparison of the two male morphs is velopment). Does cell robbing or cleptoparasitism presented elsewhere (Danforth 1991). occur under such circumstances? And finally, do Materials and Methods 1 Current address: Department of Entomology, National Mu- seum of Natural History, Smithsonian Institution, Washington, Perdita portalis has been collected from north- D.C. 20560. central Arizona east to the southwestern corner of 0013-8746/91 /0537-0548$02.00/0 © 1991 Entomological Society of America 538 ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA Vol. 84, no. 5 New Mexico (Hidalgo, Grant, and Luna counties) was gently packed into the wire enclosure on the and south to Zacatecas state, Mexico (Timberlake Plexiglas plate with a rolling pin. When the soil 1954, 1968). Adult foraging is restricted to species was packed tightly enough that tunnels could be of Sphaeralcea. cut into the soil with a razor blade, no more soil This study was conducted at a locality 2 km north was added. A simple system of tunnels and cells, of Rodeo, Hidalgo County, where ~10 nests in with one main tunnel leading to the opening at the 1987, 24 nests in 1988, and 33 nests in 1989 were top of the plate connected to laterals leading to located. Nests were also found at other localities: cells, was cut into the packed soil surface (Fig. IB). 30 km north of Hachita, Grant County (1988) and Pupae were then placed into the artificial cells with 9.2 km east of Animas, Hidalgo County (1989). All their heads facing toward the main tunnel. From localities were mixed Chihuahuan desert-grassland 2 to 10 female pupae were placed in each obser- habitat with scattered Sphaeralcea plants, the sole vation nest and, in some nests, 1-6 male pupae. source of pollen and nectar for this species. Sphaer- Finally, another rectangular piece of red Plexiglas alcea subhastata Coulter predominates at the Ro- of the same size was placed on top and clamped deo locality and S. angustifolia (Cavanilles) at the into place with 5.1-cm (2 in.) paper binder clips Animas locality. All nests were found in patches of (Fig. 1C). It was important to clean the surface of fine claylike soil devoid of vegetation. the wire gasket before attaching the top plate to Nests 2 km north of Rodeo were mapped in 1988 ensure a tight seal between plate and gasket. Nests and 1989 to determine the frequency of nest reuse were kept upright in an incubator at 30°C for 1- and new nest founding from year to year. As at 2 d before they were placed in the field. the other localities, nests were located only in areas In this study, unlike previous studies of halictine of exposed soil devoid of vegetation. Five such bees in which observation nests were placed in areas were found on the west side of a dirt road indoor flight rooms (Batra 1964, 1968, 1970; Stock- that extended northeast from Highway 80 to a cattle hammer 1966; Kukuk & Schwarz 1987,1988), nests tank and a wind-operated water pump. The five were placed in the field so that bees could forage patches together stretched «110 m. To map nests under natural conditions (Fig. ID). To do this, a accurately, a metal stake was placed roughly at the hole (1.5 m deep, 1.5 m wide, 2 m long) was dug center of each of the five areas and all nests were at the Rodeo locality and covered with a 1.9-cm mapped with respect to the central stakes. The (% in.) plywood top fitted with a trap door (Fig. 2). metal stakes were then mapped with respect to Four slots (1.0 by 20.3 cm) were cut along one edge each other. Mapping was done using a hand-held of the plywood top into which the uppermost edges compass and a 50-m measuring tape. of the observation nests could be fitted. The nests Nests were excavated by blowing a fine mist of were supported from beneath by a wooden shelf. talcum powder down the tunnels and carefully dig- The entire plywood lid (except the trap door) was ging away the soil with a penknife. Care was taken covered with a thin layer of soil. to excavate nests early or late in the day or on When adult bees eclosed in such nests, they fol- cloudy days to ensure that all resident bees would lowed the artificial main tunnel and then dug the be present. Larvae and pupae were placed in 96- remaining 3-4 cm of soil to the surface. In 1988, well tissue culture dishes for rearing in a laboratory seven nests were constructed and three were even- incubator at 30°C and 100% RH. tually accepted by at least one female and one The body weights of adult bees and pollen balls macrocephalic male. In 1989, six nests were con- were measured after they had been dried for at structed and three were accepted by at least one least 2 d at 55°C (dry weight). Prepupae (postdefe- female. Large-headed males were deliberately ex- cating, last instars) were weighed live. Weights were cluded from the 1989 nests to observe female be- measured to the nearest 0.01 mg. havior in their absence: a situation like that in new- Observation nests, similar to those used to study ly initiated nests before the emergence of the first intranest behavior in Lasioglossum zephyrum macrocephalic males. Observation nests contained (Halictidae) (Michener & Brothers 1971), were at most six adult females and four adult macro- constructed in the following way. Each observation cephalic males. Fifty-six cells were completed in nest consisted of a thin layer of soil sandwiched the six successful observation nests. In one nest, a between two transparent red Plexiglas plates, with single cell was completed by the solitary female a soil thickness equal to the diameter of tunnels resident; whereas, in another nest, 24 cells were and cells in natural nests (2.2-2.5 mm in diameter).