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. H. ligatus, like Lasioglossum zephyrus, 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.

Halictus ligatus was originally described by Thomas Say in 1837. 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. 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.

Taxonomy and phylogeny

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. 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. 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.

Description and identification

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 for 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  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.

Distribution and habitat

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. 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.

Colony cycle

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


Aggression
H. ligatus is a primitively eusocial species meaning that there is suppression of ovarian development in female workers by aggressive behavior of the queen. Aggression is most common in the queen of the nest, but it may be exhibited by other members, especially if the nest is larger. The inhibition of ovarian development is accomplished by phermonal secretions and aggressive acts by the queen, who is trying to maintain herself as the sole egg layer. When there is a nest with multiple foundresses, one will assume the reproductive duties and become a guard while, the other a forager. This guard will protect the nest from intruders and assume a C- shape with the head and stinger directed toward an intruder to threaten them. Familiar members of the nest are allowed in based on familiarity, age, and smell  If a queen happens to die during the season when the nest is still highly active a replacement queen will be chosen from the workers, who will begin to exhibit the same types of behaviours as the previous queen. When climate is harsh or breeding season becomes short, some members of the colony may become socially polymorphic and revert to a solitary lifestyle, an adaptation to varying environmental conditions.

Defense
In the rare occurrence of nests which contain more than one foundress, one individual will become the "guard". These guards are reproductively dominant individuals, while other individuals assume foraging duties. Single foundress nests, however, are left unguarded during foraging trips. As a result, these nests may be prone to experience conflict over nest ownership due to the occurrence of usurpation attempts. These conflicts range from brief feuds of 5 seconds or less to prolonged fights lasting anywhere from 10 to 26 minutes. During these encounters, the guard blocks the nest entrance with its abdomen and engages in thrusts to eject the intruder. In fact, this may even involve mandibular aggression, which often leads to the loss of legs and other vital body parts.

Provisioning
Due to the correlation between female body size and role in the colony, it becomes evident that larval diet plays an integral part in caste differentiation and sociality for H. ligatus. In fact, the mother bee is often seen limiting the amount of resources and nutritious intake she provides to her offspring so that they are forced to develop into small and lean females. This deliberate behavior ensures that these daughters are suitable for their roles as helpers, as a result of their incapability to perform independent reproduction. Furthermore, small-bodied females may be desirable as they are much easier to manipulate into a subordinate role with the use of dominance interactions and aggression.

Behavior

Worker-queen conflict
In established nests, workers may directly compete with the queen as well as each other for oviposition, and attempt to lay their own eggs though many workers forgo their own reproduction and provision for others' offspring. However, many other workers lay eggs, thereby raising their own offspring in addition to the queen's. In fact, around half of H. ligatus workers are inseminated and actually capable of producing diploid eggs.

Kin selection

Although pollen protein content is commonly considered the most important factor for bees, different pollens are known to vary widely by many nutritional factors. For H. ligatus, a polylectic, social halictine, offspring mass increases with increasing protein content in a linear manner. This suggests that smaller amounts of high protein pollen are needed to produce an offspring of a given size relative to the required amount of pollen of lower pollen content. However, size of provision masses does not vary with pollen type, indicating that foragers are not able to recognize protein content differences.
Pollination
H. ligatus are a generalist species when pollinating  and will pollinate a variety of different plants via their foragers. Much of the pollen collected will become part of the provisions in the nest, but many stigmas of plants are pollinated while foragers are collecting what they need.

Pollen transport
The amount of provisions that can be carried per foraging trip varies widely across different bee species. H. ligatus, for instance, participates in dry external pollen transport as opposed to internal transported or agglutinated external transport. This type of pollen transport allows for more rapid pollen loading than the agglutination as it omits the step of nectar addition.

Diet

Weather pattern differences from year to year and other environmental factors effect the ways in which H. ligatus develop. Changes in weather patterns can result in significant body size variation in all castes of the colony. H. ligatus are ectothermic organisms meaning that both food availability and temperature have significant effects on development and body size. At higher temperatures, ectothermic insects develop faster causing them to move from one larval stage to the next at a faster pace and then spend less time feeding as juveniles. Due to this, those insects will be smaller when they enter their adult stage compared to those who had more time eat as juveniles.

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