Seasonal change of nest survival and related aspects in an aggregation of Lasioglossum duplex (Dalla torre), a eusocial halictine bee (Hymenoptera: Halictidae)

Abstract

SummaryNest survival in an aggregation of a eusocial halictine bee, Lasioglossum duplex, was censused through an annual cycle. Out of 2,500 nests marked at the beginning of solitary phase in the spring, only 25.5% attained eusocial phase. But 60.5% of 636 nests attaining eusocial phase successfully produced sexual offspring. This shows that solitary phase is the most vulnerable period in the annual cycle.A very low productivity in eusocial phase in the census year was clarified from examination of 99 nests in the autumn. The number of prospective foundresses surviving to the next year was estimated upon the number of brood cells in examined nests and of old females surviving these nests. Deviation between this estimate and the number of nests made in the next spring was 8.8%, confirming a drop of population size to less than one third in the next year. Some nests solitarily made in the summer by dispersed females were examined. Productivity in such nests was extremely low, hence these nests should contribute virtually nothing to the next generation.Possible factors affecting the low productivity in eusocial phase were enumerated though none of these were supported by concrete evidence. Some considerations were given on the relation between obtained results and colony life cycle in eusocial insects, particularly in halictine bees.

Spatio‐temporal variation of colony structure and eusociality level of the Japanese sweat bee Lasioglossum (Evylaeus) duplex (Hymenoptera: Halictidae)

“…In Lasioglossum duplex, however, the mortality of foundresses is about 25% (Sakagami and Hayashida 1968) and the ''succession of queens'' hypothesis is unlikely. Instead, Sakagami (1977) found a few L. duplex nests constructed by solitary females in summer when most colonies were eusocial. In the present study, the number of adult females sharply decreased soon after the eclosion of new adults, suggesting that some females leave their natal nests without becoming workers.…”

“…In the present study, brood size, sex ratio and queenworker size dimorphism all showed geographical and/or temporal variations, many of which were statistically significant. Thus, the eusociality level is variable even in Lasioglossum duplex, which has been considered to be eusocial in all populations (Sakagami and Hayashida 1958;Sakagami 1977;Goukon et al 1986). Although worker reproductivity was not clear in the present study, the presence of workers with developed ovaries and/or corpora lutea suggests that a few workers lay eggs.…”

“…Lasioglossum (Evylaeus) duplex is a common species in northern Japan, and previous studies by Sakagami and colleagues have indicated that colonies of this species exhibit primitively eusocial behavior (Sakagami 1977;Sakagami and Hayashida 1958, 1960, 1961, 1968Goukon et al 1986). Here, we present data from a recent study on two populations of this species which reveal geographical variation, and we compare our data with those of Sakagami and his colleagues to examine temporal variation in the same population.…”

Flower visitors of lettuce under field and enclosure conditions

“…Especially in the ground nesting bees, all nests were marked by placing a numbered small flag near each nest entrance. Conditions of entrances (shape, size and color) were recorded every evening and/or morning to estimate the state of bee activity (see Sakagami, 1977). Based on these data and the weather conditions, activities of each bee are presented as the visitation frequency (total days of visitation to lettuce flower/total days of flight activity performed by the insect) for each insect as a visitation constancy for the lettuce.…”

Both cooperation and nest position improve larval survival in the sweat bee, Lasioglossum (Evylaeus) baleicum

“…Sweat bees have been reported to aggregate their nests within a small area (Sakagami 1977;Sakagami and Fukuda 1989;Cronin and Hirata 2003;Hirata 2005;Richards et al 2005;Hirata and Higashi 2008;Ulrich et al 2009), raising the question as to whether the location of a nest within such an aggregation affects larval survival. Since predator attacks originate from outside these nesting areas, peripheral nests are likely to be the most susceptible to predation.…”