Halictus ligatus is a species of sweat bee from the family Halictidae, among the species that mine or burrow into the ground to create their nests.bee. (2013). In Encyclopædia Britannica. Retrieved from http://www.britannica.com/EBchecked/topic/58219/bee H. ligatus, like Lasioglossum zephyrusBatra, S.W.T. (1966) The life cycle and behavior of the primitively social bee Lasioglossum zephyrum (Halictidae). Univ. Kansas Sci. Bull. 46: 359–423., is a primitively eusocial bee species, in which aggression is one of the most influential behaviors for establishing hierarchy within the colony, and H. ligatus exhibits both reproductive division of labor and overlapping generations.
Taxonomy and phylogeny Halictus ligatus was originally described by Thomas Say in 1837.Carman, Geoffrey M., and Laurence Packer (1996) "A cryptic species allied to Halictus ligatus Say (Hymenoptera: Halictidae) detected by allozyme electrophoresis." Journal of the Kansas Entomological Society 69 (suppl.): 168-176. The genus name Halictus refers to a group of sweat bees of the family Halictidae and order Hymenoptera known for their eusocial behavior and underground nesting.Danforth, Bryan N. "Evolution of sociality in a primitively eusocial lineage of bees." Proceedings of the National Academy of Sciences 99.1 (2002):286-290 Within Halictidae, the subfamily Halictinae is unique for the substantial diversity in social behavior exhibited among species or within species, such as in H. rubicundus. For instance, species of this subfamily may exhibit either solitary nesting, communal nesting, cleptoparasitism, social parasitism, or primitive eusociality similar to H. ligatus.
Description and identification The appearance of H. ligatus individuals closely resembles other members of the genus Halictus. These individuals are easily differentiated from those of the closely related Lasioglossum by the presence of their pale fasciae hair bands on the posterior margins of the metasomal terga.Roberts, Radclyffe Burnand. Bees of northwestern America: Halictus (Hymenoptera: Halictidae). Corvallis: Agricultural Experiment Station, Oregon State University, 1973. In addition, the species is predominantly black or brown-black and lacks the faint metallic tints found in bees of the Seladonia subgenus. Moreover, species of Halictus are generally larger than species of Seladonia which are typically under 7 mm long.
H. ligatus females are easily distinguished from other females by a postero-ventral genal tooth. In addition, the males are easily distinguished from other males by the presence of long suberect hairs on the second and third metasomal sterna.
Female physical distinctions based on role For H. ligatus, similar to other eusocial halictids, the differences in reproductive strategies among females correlate with distinctions in body size and appearance.Brand, N. & Chapuisat, M. 2012. Born to be bee, fed to be worker? The caste system of a primitively eusocial insect. Frontiers in Zoology, 9, 1-9. For instance foundresses, or queens, tend to be large-bodied females in order to maximize energetic reserves, thereby enabling them to overwinter, establish nests, and reproduce independently. On the contrary, helpers tend to be smaller-bodied daughters with undeveloped ovaries.
Distribution and habitat
Halictus ligatus is one of the most abundant and readily identifiable bees in North America, encompassing a wide range of aridities and altitudes. The species can be found in North American from about 50 degrees north latitude, south to the West Indies and Colombia. H. ligatus is also located in temperate areas of the Atlantic to the Pacific, including the southern Gulf of Mexico and southern Canada.Richards, M. H. 2004. Annual and social variation in foraging effort of the obligately eusocial sweat bee, Halictus ligatus (Hymenoptera: Halictidae). Journal of the Kansas Entomological Society, 77, 484-502. This vast range of distribution contributes to local distinctions in behavior, colony cycle, and colony demographic as a result of variation in environmental pressures.
Nest H. ligatus typically nests in level, well-drained, hard-packed soil free of vegetation. As a result, these nests are most frequently encountered in dense aggregations in dirt roads and paths. The tendency for H. ligatus to nest in aggregations is advantageous for the cooperation of bees for the repulsion of parasites. However, this behavior can also be disadvantageous as it minimizes the time spent by predators in search of prey, or parasites in search of hosts.
Nest initiation In general, H. ligatus will continue to utilize a nest site year after year until it becomes too crowded as a result of encroaching vegetation or parasites and diseases. The overwintered queens actually prefer to remodel old nests in order to initiate new nests. Presumably, those bees which nest at old sites and in old nests tend to produce a greater number of descendants than those who nest elsewhere. As a result, selection favors the continued use of this site. However, in situations in which a sudden catastrophe has eliminated the original nesting site, the bees will of course be forced to select a new site. This new site will be selected favoring those bees who have already dispersed, in an effort to select individuals who possess the tendency to disperse again in the future.
Nest construction The nests of H. ligatus occur either in rotting wood or within the ground.Richards, Miriam H., and Laurence Packer (1996) "The socioecology of body size variation in the primitively eusocial sweat bee, Halictus ligatus (Hymenoptera: Halictidae)." Oikos 77: 68-76. They have diverse ways of setting up ground nests which can include small cells, scattered cells, and clusters of cells depending on the size of the colony. Nests inside rotting wood are usually irregular in shape due to the constraints of their medium. The area around the cells is usually uncovered and the cells are lined with a waxy substance from the Dufour's gland of the bee.Eickwort GC, Eickwort KR. 1973. Notes on the nests of three wood-dwelling species of Augochlora from Costa Rica (Hymenoptera: Halictidae). Journal of the Kansas Entomological Society 46: 17-22. which is used to protect developing bees.
Colony cycle In north temperate regions, H, ligatus has an annual colony cycle similar to that which is found in almost all other halictines, or social sweat bees, during which the cold winter ensures several months of complete inactivity during which only young gynes survive.Packer, Laurence, and Gerd Knerer. "The biology of a subtropical population of Halictus ligatus Say (Hymenoptera; Halictidae). III. The Transition between annual and continuously brooded colony cycles." Journal of the Kansas Entomological Society (1987): 510-516. Following this period, these individuals undergo a burst of nest initiation in the spring and produce workers during the summer before switching to male and gyne production in the late summer and autumn. In this context, "gynes" are defined as females that are unworn and have no ovarian development. Gynes will overwinter and later become foundresses by initiating nests in the spring. As a result, bees collected towards the end of the colony cycle display a larger proportion of males and young gynes than earlier samples.
However, in the extreme south of Florida, H. ligatus is continuously brooded and multivoltine; having overlapping colony cycles with one complete cycle lasting for up to a few months, with the inclusion of an option break in activity in areas with a pronounced dry season. In addition, individuals in this region experience markedly reduced reproductive division of labor as compared to those who participate in the annual colony cycle. As a result, bees collected towards the end of this colony cycle display an increase in the proportion of newly emerged gynes, an increase in the proportion of female bees that are mated, an increase in the proportion of males, and a morphological caste differentiation indicating that the gynes are larger than the worker bees.
Behavior Dominance hierarchy The vast range of distribution contributes to the variations in behavior and dominance hierarchy observed for individuals of the species living in different environments. For instance studies indicate that annual variation in local weather conditions actually directly influences the demography of these sweat bee colonies, thereby indirectly influencing the nature of social interactions among adult females. In fact, habitats experiencing adverse conditions caused by excessive rainfall resulted in poor brood survival, production of fewer workers, and queen-dominated oviposition. Under more favorable conditions such as warm weather, it was found that colony and brood survival was high, large numbers of workers were produced, and workers were responsible for a larger proportion of eggs laid in the reproductive brood. These distinctions in environment may also affect colony size and decrease eusociality. For instance, in southern areas with long nesting seasons where there are a large number of workers per nest, queen control of worker behavior is less effective than in northern areas with shorter nesting seasons where there are fewer workers per nest.
Division of labor Female reproductive roles Female sweat bees of H. ligatus exhibit a wide range of reproductive roles, ranging from typically foundress (or queen-like) to typically worker-like.Richards, M. H., and L. Packer (1998) "Demography and relatedness in multiple-foundress nests of the social sweat bee, Halictus ligatus." Insectes Sociaux 45: 97-109. Nests founded in the spring are mostly haplometrotic or founded by a single queen. A few others, around 12%, are pleometrotic or founded by anywhere from 2 to 6 queens. In these pleiometric associations, dominant foundresses behave in a manner similar to haplometrotic queens while subordinates behave like mid-summer workers.
The choice of reproductive role available to a particular female is generally dictated by several important factors at the time of emergence including social milieu of the nest, body size and fat stores at eclosion, and time of year. For instance, females that emerge in mid-summer that are small, have few or no fat stores, and whose nesting includes a larger queen tend to develop as workers who assist their mothers to raise the second, reproductive brood. On the contrary, females that emerge in late summer that are large and have large fat stores are destined to mate and become queens of their own nests in the following spring.
Role of the queen Typical queens in single foundress colonies exhibit behaviors consisting of solitary nest excavation and spring provisioning for the brood followed by queen-type behavior after the mid-summer emergency of workers. These behaviors include ceasing to forage and instead overlooking the workers of the colony. For colonies in which there exist multiple foundress associations, subordinates continue to forage while their social role more closely resembles that of a mid-summer worker as opposed to a haplometrotic spring queen.
Role of the worker H. ligatus worker individuals experience varying levels of eusocial behavior and colony organization depending on the environmental conditions. For instance, under harsher environmental conditions, there is more classical eusocial behavior. Therefore, the reproductive efforts of workers are generally focused on assisting the queen to raise the queen's reproductive offspring by tending to eggs, cleaning the facility, and foraging for food and water. However, under gentler environmental conditions, there is a reduction in overall eusociality. As a result, workers tend to focus more on raising their own reproductive offspring, including gynes.
Aggression