The oldest fossil bee: Apoid history, evolutionary stasis, and antiquity of social behavior.

Trigona prisca, a stingless honey bee (Apidae; Meliponinae), is reported from Cretaceous New Jersey amber (96-74 million years before present). This is about twice the age of the oldest previously known fossil bee, although Trigona is one of the most derived bee genera. T. prisca is closely similar to modern neotropical species. Most of bee evolution probably occurred during the approximately 50 million years between the beginning of the Cretaceous when flowering plants (on which bees depend) appeared and the time of T. prisca. Since then, in this phyletic line of Meliponinae, there has been almost no morphological evolution. Since the fossil is a worker, social organization had arisen by its time.

Chemistry and function of mandibular gland products of bees of the genusExoneura (Hymenoptera, Anthophoridae).

FemaleExoneura richardsoni, E. bicolor, andE. bicincta (Hymenoptera: Anthophoridae) release a pungent, staining liquid from their mandibular glands upon disturbance. This secretion is primarily composed of ethyl dodecanoate, with lesser amounts of homologous ethyl and methyl esters, salicylaldehyde, and 1,4-benzoquinone. The secretion elicits vigorous grooming when topically applied to antennae ofFormica ants. The shared, unique combination of mandibular gland lipids of these threeExoneura species supports their monophyletic classification, while the presence of salicylaldehyde may associateExoneura (Allodapini) withPithitis (Ceratinini).

Dual origin of highly social behavior among bees.

A study of behavior and structure indicates that highly eusocial behavior arose twice in the bees--i.e., in the stingless bees (Meliponinae) and in the honeybees (Apinae). Morphological features demonstrate the distinctiveness of these two groups and the relationship of the latter to bumblebees (Bombini) and orchid bees (Euglossin). The social behaviors of the stingless bees and honeybees, while more or less equally elaborate, are so different as to support their independent origins. The primitive apids, along with the related Xylocopinae (in the Anthophoridae), appear to have had the potential for parasocial, subsocial, and primitively eusocial behavior and from such forms the two highly eusocial groups arose.

Individual odor differences and their social functions in insects.

The evolution of individual or subgroup differences in odors of halictine bees is suggested from possible widespread intraspecific variation in pheromones. An important result of such variation may be maintenance of genetic polymorphisms; in nesting Hymenoptera odor differences may also facilitate individual nest recognition. In Lasioglosum zephyrum males habituate to odors of different females and perhaps thus save time by not trying to copulate with nonreceptive individuals. Guards (females) at nest entrances distinguish their few nestmates (other females) from other conspecific individuals by odors, seemingly pheromones. Duration of the habituation in L. zephyrum is at least an hour (perhaps much more) for males in relation to females and 6 or 7 days for guards in relation to nestmates. Studies of pheromones should take into consideration the possibility of pheromonal polymorphism in any species and the likelihood that it may be significant from biological and practical viewpoints.

Were workers of eusocial hymenoptera initially altruistic or oppressed?

Studies of a primitively eusocial halictid bee, Lasioglossum zephyrum, strongly suggest that a major factor in originating a worker caste is selection at the individual level for queens that control associated adult females. Even in this scarcely social form, the queen inhibits other adult females from becoming queens, perhaps by her high level of activity and frequent nudging in the nest. Queens are behaviorally less varied than workers and show specialization, particularly in frequency of nudging (which is concentrated on the worker with largest ovaries) and of backing. Backing draws workers, especially those with slender ovaries, down to lower parts of the burrows where the stimuli for cell construction and provisioning probably operate. Eating of worker-laid eggs by queens was also noted. In spite of the suggestion that queens have evolved to control their workers rather than that workers have evolved to help their queens, both may well have occurred, for these processes are not mutually exclusive; moreover, social attributes mutually beneficial to both castes no doubt have arisen.

Interactions in Colonies of Primitively Social Bees: Artificial Colonies of Lasioglossum zephyrum.

Lasioglossum zephyrum usually lives in small colonies but is facultatively solitary. Lone bees and colonies produced from female pupae of the same generation were established in artificial indoor nests. Both the length of the prereproductive period and the number of cells produced per bee per day decreased with increasing colony size. In most colonies, ovarially and behaviorally recognized castes arose, a queen and workers, but with all intergradations. The mean size of queens was larger than that of workers. Nearly all queens mated although few workers did so in rooms with a few males, but mating had no effect on subsequent behavior or ovarian development. In groups of diverse age there was a tendency for the oldest bees to be queens; queens also were larger on the average than workers. In groups of equal age, the largest bee was most often queen. As would be expected for a scarcely social species, mechanisms of social integration (resulting in division of labor and differentiation of castes) mostly appear to involve behavioral features of the solitary ancestors and accidental results of joint occupancy of nests. There is no evidence of direct food or pheromone transfer among adult bees.