Halictus ligatus

Halictus ligatus
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Halictidae
Genus:	Halictus
Species:	H. ligatus
Binomial name
Halictus ligatus unknown

Halictus ligatus is a species of sweat bee from the family Halictidae, characterized by those bees that mine or burrow into the ground to create their nests,^[1] which is one of the most common families of bees that live in temperate areas of the world.^[2] The term sweat bee is the common name used for Halictus ligatus because they are attracted to the salts of human perspiration. Most are small to medium in size, ranging from three to ten millimetres in length ^[3] These bees may be metallic or non-metallic in appearance and are one of the most abundant species other than the Apis or honeybee.^[4] In general, the family Halictidae shows graduations in social behaviour as species can be solitary, communal, semi-social or eusocial.^[2]

Halictus ligatus itself is a primitively eusocial species that has overlapping generations for reproduction and division of labor purposes.^[5] It nests within the ground and starts new colonies with overwintered fertilized females in late spring.^[6] The colonies themselves typically have one queen but instances of multiple queens or even queenless nests do occur.^[7] Aggression plays a large role in the production of the hive.^[5] Queens can exhibit highly aggressive behaviour which enables them to suppress ovarian development in other female workers allowing them to be sole producer of the next brood. This is this case in most smaller nests but, in larger nests this dynamic is harder to maintain and some female workers are able to reproduce.These aggressive behaviours from the queen also function to establish dominance hierarchies within the nest ^[5] Body size variations occur across a colony of Halictus ligatus and are highly dependent on environmental conditions ^[6] which play a huge role in how large a nest will be and how the next generation will be established.

Location

Halictus ligatus has considerable geographic variation in colony organization and is located in temperate areas of the Atlantic to the Pacific, including the southern Gulf of Mexico^[8] and southern Canada ^[9]

Nests

The nests of Halictus ligatus occur either in rotting wood or within the ground.^[6] 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 Dulfor gland of the bee.^[10] which is used to protect developing bees.

Environmental Influences

Weather pattern differences from year to year and other environmental factors effect the ways in which Halictus ligatus develop. Changes in weather patterns can result in significant body size variation in all castes of the colony.^[9] Halictus ligatus are ectothermic organisms meaning that both food availability and temperature have significant effects on development and body size.^[6] 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. Also, populations of Halictus ligatus from milder climates, those with less rainfall, experience diminished eusocial activity as compared to those who are exposed to excessive amounts of rainfall. In this case, the workers shift their reproductive priorities from assisting the queen, to producing a brood of their own within the nest, some of which may become a new founder for a nest the next spring.^[6] Warmer, drier conditions are ideal for Halictus ligatus especially because they nest either in the ground or near to it. When these warm and dry conditions occur colony brood and survival become higher, the queen will produce a large number of workers, and these workers will begin to lay a large proportion of the eggs in the reproductive brood since the queen is not able to reproductively suppress such a large amount of workers ^[9]

Life Cycle

The life cycle of Halictus ligatus consists of two main stages: the overwintering and the active stage. The nest, which occurs within burrows in the ground or rotting wood, begins to become active and bees awake from their hibernal diapause in late April to early June, but will not leave their overwintering burrows until late June.^[7] Hibernal diapause is a delayed development that occurs in many insects where there is no growth and feeding of larvae, embryonic and pupal development stops, and mating, reproduction, and egg development of adults does not occur.^[11] Nests are established by a single female bee, who has mated and laid eggs last spring, called the foundress, but there have also been instances where multiple bees may start a nest together. The foundress will forage for several weeks in early June to provide for the first brood which will be composed of mostly of small females, who become workers, and a few males ^[9] Once the workers have emerged, they start to forage and will produce their own reproductive brood that is composed of both males and females. The females in this group are called gynes and they are those that overwinter and enter hibernal diapause to become foundresses the following spring ^[5] and after they emerge they mate and dig an overwintering tunnel beneath the one they came from and enter diapause.^[6]
Halictus ligatus are mass provisoners meaning that they will construct a mass of pollen and nectar which will be the sole source of food for the developing larva and the larvae will not pupate until they have consumed the entire pollen mass.^[9] Daughters of the first brood may become non-reproductive helpers that either forage or stay in their natal nest to assist the queen in raising the next brood, or will reproduce in their natal nest, will find other nests to reproduce in, or enter diapause early and become a foundress in the next spring.^[12] In most cases, when there are larger colonies, queens will produce the eggs that become males wheres workers will produce gyne destined eggs.^[13] Within a single foundress colony the average relatedness is 0.5, implying that the queens will use equal amounts of sperm from two males that are not related.^[13] This is only able to occur because workers have maintained their ancestral abilities of being able to breed independently, which has direct fitness benefits for the worker through reproduction and indirect fitness benefits by being able to help relatives.^[12] This is why, in larger colonies, workers are more likely to reproduce as it increases the genetic diversity of the nest allowing for a better proliferation of the species.

Pollination

Halictus ligatus are a generalist species when pollinating ^[14] 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.^[14]

Eusociality and aggressive behaviour

Halictus ligatus is a primitively eusocial species meaning that there is suppression of ovarian development in female workers by aggressive behaviour 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.^[7] 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 ^[5] 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 ^[15] When climate is harsh or breeding season becomes short, some members of the colony may become socially polymorphic and revert to a solitary lifestyle ^[16] which an adaptation to varying environmental conditions.

References

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