Augochlorella striata, Lasioglossum (Evylaeus) cinctipes, Lasioglossum (Evylaeus) comagenense, and Lasioglossum (Dialictus) laevissimum were studied on Cape Breton Island, Nova Scotia, throughout their flight season in 1987. The weather during the summer was unusually good, with above-average temperatures and hours of sunshine but very low rainfall. Conversely, the previous summer had been very poor for bees, with comparatively few days suitable for foraging, particularly in July. Augochlorella striata was basically solitary but some nests produced one or, at most, two workers, thereby becoming eusocial. In other localities, L. cinctipes is known to be eusocial with well-developed morphological and physiological caste differentiation. However, most foundresses observed in 1987 were extremely small, smaller than usual for workers elsewhere, and none of the more than 100 nests produced adult workers or a reproductive brood. Most foundresses were either survivors of the worker brood from the previous year or unusually small reproductive brood females produced as a result of the bad weather in 1986. Lasioglossum comagenense was solitary or semisocial with one to four females occupying a nest. Lasioglossum laevissimum exhibited significant levels of pleometrosis and an extended period of worker foraging in summer. A comparison of the productivities of these four species indicates the importance of a flexible social system in a marginal climate.

PACKER, L., SAMPSON, B., LOCKERBIE, C., and JESSOME, V. 1989. Nest architecture and brood mortality in four species of sweat bee (Hymenoptera; Halictidae) from Cape Breton Island. Can. J. Zool. 67: 2864 -2870. The nest architecture of four species of the bee family Halictidae from Cape Breton Island, Nova Scotia, was studied. Augochlorella striata and Lusioglossum (Evylaeus) comugenense constructed their brood cells in a cluster surrounded by a cavity. In the case of A. striata, the cavity-forming habit increased the rate at which the soil of the brood cell cluster dried out, relative to the surrounding soil. The year of the study was unusually dry and in midsummer the moisture content of the soil was extremely low. This weather pattern seemed to result in some mortality of A. striata brood due to dehydration, and prevented foundresses from constructing brood cells. The two other species, Lusioglossum (Evylaeus) cinctipes and Lusioglossum (Dialictus) laevissimum, did not construct brood cell clusters. All four species had shallower nests than other species with similar nest architectures for which published data are available. All species except L. laevissimum nested in association with stones at the ground surface. It was shown that brood cells of nests situated close to rocks and stones were likely to experience increased temperature, presumably resulting in a faster developmental rate for immatures. This may be important in the Cape Breton environment, which is clearly marginal for social sweat bees. Both A. striata and L. comagenense exhibited very low mortality rates in developing immatures (1 and 7%, respectively). PACKER, L., SAMPSON, B., LOCKERBIE, C., et JESSOME, V. 1989. Nest architecture and brood mortality in four species of sweat bee (Hymenoptera; Halictidae) from Cape Breton Island. Can. J. Zool. 67 : 2864-2870. On trouvera ici des donntes sur l'architecture des nids de quatre espkces d9Halictidae de 1'Ple du Cap-Breton, Nouvelle~c o s s e . Chez Augochlorella striata et Lusioglossum (Evylaeus) comugenense, les cellules larvaires sont rassemblkes en groupes et entourkes d'une cavitC. Dans le cas d'A. striata, la formation de la cavitk entrafne la dkshydratation plus rapide de la terre qui forme les cellules que du sol environnant. L'annke de 1'Ctude s'est avkrke une annke particulikrement skche et, au milieu de l'ktk, le contenu hydrique du sol Ctait extremement bas. Ces conditions semblent avoir entrain6 une certaine mortalitk par dkshydratation au sein du nid des A. striata et elles ont empechk les fondatrices de construire de nouvelles cellules larvaires. Les abeilles des deux autres espkces, Lusioglossum (Evylaeus) cinctipes et Lusioglossum (Dialictus) laevissimum, n'ont pas construit de cellules regroupkes. Les quatre espkces avaient des nids peu profonds par comparaison aux donnkes de la littCrature sur d'autres espkces B nids d'architecture semblable. Chez toutes les espkces, sauf chez L. laevissimum, les nids ktaient associCs B des pierres B la surface du sol. 1' 1 a Ct C dCmontrk que les ce...