Behavioral Interactions Among Females of Acamptopoeum submetallicum (Spinola) and Nolanomelissa toroi Rozen (Hymenoptera: Andrenidae)

Wepresent the results of circle tube experiments performed upon a solitary panurgine bee Acamptopoeum submetallicum (Spinola) and the enigmatic Nolanomelissa toroi Rozen. As expected for a solitary species, females of A. submetallicum generally avoided one another. In contrast, N. toroi exhibited high levels of aggression, as generally found among bees with a reproductive division of labor. However, dissection and phenological data on N. toroi are incompatible with either eusocial or semisocial behaviors. Furthermore, no acts of cooperation were observed in the behavioral experiments suggesting that N. toroi is not communal. The extremely female biased sex ratio and low levels of mandibular wear among mated, reproductively active females in this species remain difficult to explain. Social behavior in bees varies greatly, ity to quickly discriminate and classify bee ranging from solitary with one female per social behavior without the need for denest to eusocial with up to tens of thoutailed and laborsome nest studies, is circle sands of individuals per nest (Michener tube experiments. This experimental 1974). A solitary bee constructs her own method, introduced by Breed et al. (1978), nest and provides stored food for her offsimulates nest tunnels using clear plastic spring, while eusocial bees (sensu Michetubing, where interactions among females ner 1974) have a reproductive division of can be observed. Circle tube arenas were labor, cooperative brood rearing, and originally used to study interactions more than a single generation of adults in among different castes of eusocial bees their nests at some point in the colony cy(Breed et al. 1978; Pabalan et al. 2000) and cle. Communal behavior is a separate type to compare behaviors of species with difof social organization in which two or ferent social organizations (Kukuk 1992; more females share a nest without a reWcislo 1997). More recently it has been productive division of labor. To classify used to help predict the social organizathe behavior of bees formally, nest excation of species whose behavior is not vations at various times during the nestknown (Packer 2000; Packer et al. 2003). ing cycle accompanied by dissections of Interactions in the circle tube apparatus bees are usually needed to examine the exare initiated when two bees encounter one tent of their reproductive division of labor, another head-to-head within one body if any (Bell and Hawkins 1974; Brothers length of each other, referred to as a fronand Michener 1974; Wcislo et al. 1993). tal encounter (FE). Behavioral interactions However, such studies are time consumin circle tubes can usually be classified as \g and impossible perform in cases aggressive, cooperative, or avoidance. Agi (Packer et al. gressive interactions include one or both . A technique ay have the abilbees nudging, lunging or biting one an/olume 13, Number 1, 2004 49 )ther. Cooperative interactions involve dominance [e.g. Halictus ligatus (Pabalan ? ees passing one another, by rotating their et al. 2000) and Lasioglossum zephyrum ? ody in such a way that they pass venter(Breed et al. 1978)]. :o-venter. Lastly, avoidance interactions The behavioral repertoire of bees within nvolve one or both bees turning away the circle tube apparatus has been comrom a FE. The relative frequency of these monly reported for halictids (Breed et al. zategories of interactions in a species 1978; Smith and Weller 1989; Kukuk 1992; seems to correspond to its social organiMcConnell-Garner and Kukuk 1997; Wcis;ation (McConnell-Garner and Kukuk lo 1997; Pabalan et al. 2000; Packer 2000; L997; Paxton et al. 1999; Packer et al. 2003). Packer et al. 2003), as they are the most ntraspecific interactions among solitary behaviorally diverse bee family (reviewed :>ee species often result in avoidance inby Packer 1997; Wcislo and Danforth eractions occurring at the highest fre1997). In comparison, the behavioral rep}uency [e.g. Lasioglossum figueresi Wcislo ertoire of bees within the family AndrenWcislo 1997), L. platycephalum (Rayment), idae, has been studied only once using L (Ctenonomia) sp. (McConnell-Garner these methods (Paxton et al. 1999). Aland Kukuk 1997) and Penapis toroi Rozen though most andrenid species are solitary, Packer unpublished)]. In contrast, intrasome are communal (Paxton 1999; Michspecific interactions among individuals of ener 2000), while none are known to be a communal species result in a high fresemisocial or eusocial. Using the circle :mency of cooperative interactions [e.g. Latube apparatus, social interactions beuoglossum hemichalceum (Cockerell) (Mctween pairs of conspecific females of two ^onnell-Garner and Kukuk 1997), Ruizancommunal andrenids, Andrena scotica Perv heda mutabilis (Spinola) (Packer unpubkins and Pamirgus calcaratus Scopoli were iished) and Pamirgus calcaratus Scopoli described by Paxton et al. (1999). P. calcarTaxton et al. 1999)]. These observations atus displayed highly cooperative behavintuitively agree with the behaviors exior, while A. scotica displayed lower levels pected from the above two social organiof cooperation but both displayed very zations: females in a communal nest must low levels of aggression, share the nest entrance, and thus a high Nolanomelissa toroi Rozen, a recently level of cooperation is required, whereas described genus and species from the solitary bees generally do not interact with southern border of the Atacama Desert in other females in their nest tunnels, and Chile (Rozen 2003), has defied the atthus may lack the behavioral repertoire tempts of several melittologists to find its needed for cooperation. Intraspecific internest in places where it is abundant. Furactions among individuals of eusocial bees thermore, it has an extremely female biare more complex, as different castes ased sex ratio: only three males have been (queens, guards, and foragers) interact difseen after extensive collecting, whereas ferently with each other. For example, forhundreds of females have been observed, ager-forager interactions often result in a This study was conducted to examine if higher frequency of cooperation, than circle tube experiments could help estabguard — guard interactions [e.g. Lasiogloslish whether N. toroi is a communal spesum zephyrum (Smith) (Breed et al. 1978)]. cies, with perhaps few nest entrances per While queen — queen interactions often refemale and intranidal mating, thereby exsult in a high frequency of cooperative plaining the biased sex ratio. Communal and aggressive interactions [e.g. Halictus behavior is well known in the subfamily ligatus Say (Pabalan et al. 2000)]. Similarly, Panurginae [e.g. Macrotera texana (Cresqueen-forager interactions may be coopson) (Neff and Danforth 1992), Perdita porerative, or aggressive presumably to assert talis Timberlake (Danforth 1991), Perdita 50 Journal of Hymenoptera Research opuntiae Cockerell (Custer 1928), Panurgus calcaratus (Scopoli) (Knerer 1980), Panurginus albopilosus Lucas (Rozen 1971) and Meliturgula braunsi Friese (Rozen 1968)], and also in halictids [e.g. Lasioglossum hemichalceum ( = L. erythrurum) (Kukuk and Schwartz 1987; Kukuk and Crozier 1990) and some species of Agapostemon (Janjic and Packer 2003)]. On the assumption that N. toroi is communal, we hypothesize that its behavior in circle tubes should be consistent with this type of social organization: interacting females should show comparatively high levels of cooperation and little aggression. Acamptopoeum submetallicum (Spinola), a predominantly solitary andrenid (Rozen and Yanega 1999), was also studied for comparative purposes. Acamptopoeum submetallicum occurs in the same subfamily as N. toroi, the Panurgine (Ruz 1987), with the former belonging to tribe Calliopsini Robertson, and the latter belonging to the tribe Nolanomelissini Rozen and Ascher, which appears to be the sister group to all other Panurginae (Rozen 2003, Ascher in Rozen 2003). Weexpect avoidance, with little cooperation, to be the common mode of interaction between A. submetallicum fe-