Michener (1974) reviews the social biology of Lasioglossum duplex, one of the best studied species of sweat bees (most of the studies took place on Hokkaido, Japan). These bees construct nests by tunneling into the soil. Nests are constructed in the spring, and the bees’ active period continues through the spring and summer. Nest tunnels extend down to as deep as 30 cm. A short branch (~1 cm) tunnel leads to a cavity containing a cluster of cells arranged in an earthen comb. These combs usually contain 3-8 cells in new nests, and 4-18 later in the summer, but as many as 30 have been found in a single cluster. Bees do not necessarily finish provisioning one cell before constructing a new one; four or five cells may be in various stages of construction and/or provisioning at any one time.
Nests are initiated in the spring by mated females who have passed the previous winter in hibernation. Occasionally two females may initiate a nest together, but new nests are typically solitary, with the foundress female constructing the nest, brood cells, and foraging for pollen to provision her offspring. The first brood eggs are laid at the latter part of May. The first brood emerges as adults in late June and July. This first brood is 90% female and 10% male, except for a few nests that are 100% male, presumably because the nest foundress did not mate (unfertilized bees can only lay male eggs). These females are generally smaller than the foundresses, and become the workers in the now-social nests. They forage for pollen to provision the eggs laid by the original foundress, who is now a social queen, but do not reproduce themselves. On average this first brood contains 5 females, but because so many new spring nests fail, and thus produce no workers, the number of females in the population remains more or less constant after worker brood emergence.
During the summer, a second cluster of cells (and sometimes a third) are constructed and provisioned. Eggs for the offspring of the second brood are laid in early July, with the adults emerging in the first week of August. This brood contains both males and females, which mate with each other. The females of this brood overwinter to initiate nests the following spring, while the old queens, workers, and males die before winter.
Goukon and Sakagami (1986) give information about the biology of two populations in northern Japan. The species is common in northern Honshu. It nests gregariously (in nest aggregations). In Sapporo its life cycle is typical for temperate zone eusocial halictines: a spring solitary phase, followed by an inactive phase while brood mature, then a eusocial active phase with mating in autumn followed by overwintering. The authors note several characteristics common to both populations, including very low male production in the spring brood, high failure rate of orphaned nests in spring (the solitary phase), rarity of nest re-use, solitary overwintering in hibernacula (shelters) near the natal nest, rarity of spring co-foundresses, and virtual absence of queen replacement in summer. They also note that queens sometimes open closed cells.
This bee's nest architecture is described by Sakagami and Michener (1962). From Sakagami and Michener (1962): Nest architecture is Type Vb: Cells are oriented laterally to the main burrow, and clustered. This cluster is connected to the main burrow by a lateral burrow. The cluster is completely surrounded by a cavity created by burrowing around the cluster. Cells are arranged in combs. Nests are known from both flat ground and banks. Nests, but not cells, are re-used by subsequent generations. Number of cells in the nest: 2-9 (usually 3-8) in spring; 3-41 (usually 6-10) later. Number of females in the nest: 1 in spring, 1-6 later.
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