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Xylocopa pubescensis a species of large carpenter bee. They are known to form both solitary and primitive social nests, most often in dead or soft wood. A common area of study in X. pubescens is their dominance hierarchy and guarding behavior.

Taxonomy and Phylogeny
Xylocopa pubescens belongs to the Xylocopa genus in the subfamily Xylocopinae, a genus composed of over 400 species of large carpenter bees. It is a member of the subgenus Koptortosoma, which is the largest Xylocopa subgenus and is widely distributed with over 200 species. X. pubescens is polyphyletic and comes from a sister lineage of mesotrichia.

Description and Identification
X. pubescens is a large carpenter bee. Females are large, sturdy, shiny, and black with yellow markings on their heads. Males have a yellow pubescence that covers their entire bodies. They also are smaller than females and have a narrower head.

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Range
X. Pubescens has been found throughout Israel and the Mediterranean basin. It ranges from Southeast Asia to Northeast and West Africa. It is found in these relatively warm areas as it requires a minimum temperature of 18 degrees Celsius in order to forage.

Nest Structure
Nests can be found in dead and soft wood, as well as the wood of some man-made buildings. X. pubescens makes its nest in dead tree trunks, sticks, canes, branches, or soft wood such as eucalyptus. These nests are sinuous, branched nest typified by short tunnels. Entrance holes are 1.1-1.3 cm diameter, a widened entryway leads into a chamber that is 1.8-1.2 cm. Tunnels 1.4-1.8 cm in diameter start at chamber, follow grain, and are 5-7 cm long, consisting of few cells each. Females enlarge nest by digging new tunnels when progeny in late larval or pupal stage. Progeny often make their own tunnels in the same tunnel complex as the mother, branching off from the common chamber with the mother’s exit hole as the only access to outside. Females can extend tunnels or excavate new nests each nesting cycle. They occasionally widen current tunnels .5-1 mm each cycle. The excavating of the nests is done with mandibles.

Colony Cycle
Colonies can be founded throughout the breeding season, which takes place from the beginning of March to the beginning of November depending on ecological conditions. They are founded solitarily, with only one female. Brood is produced continuously as long as space and resources are available. Young males and females emerge from the beginning of May until the end of the breeding season in November. Overlapping generations can be found in nests starting at the beginning of May. All spring nests contain only one bee (either a young female or an old female who has overwintered) until the progeny of the bee enter the pupal stage. After that, between 1-8 adult females may be present at one time as new adults remain in the nest for up to 2 weeks. Colony and nesting cycles coincide.

Ontogenesis
Eggs are laid on bee bread in short tunnels in the nest, each containing 1-3 progeny each. When the larvae emerge from their eggs, they feed on the bee bread and go through two stages of molting before the pre-pupal stage. The first progeny to emerge will push its siblings father into the tunnel and take over the vacated space. The pre-pupal stage lasts several days before pupation. All pupae begin white and grow darker with time before turning into adults. Total developmental time from egg to adult is around 45-49 days, lasting somewhat less in the summer.

Female Takeovers
There is one reproductively dominant female in each nest. Becoming the dominant female in a nest requires a takeover from the previous dominant female. This can be done by either a nest mate, usually a daughter, or an outside intruder. In takeover attempts, fighting occurs and the defeated female either remains in the nest as a guard or leaves to attempt to found or take over another nest. After a takeover occurs, the new dominant female destroys most or all of the old brood. Then, the dominant female must determine whether or not she will allow the defeated female to remain as a guard. Factors that play into this decision are age and relatedness, as a younger female guard is more likely to try to takeover the nest in the future, as is a guard who is less related to the current dominant female. However, reproductive output has been shown to increase in guarded nests. If the defeated female is allowed to remain, she must decide whether or not to do so. This decision weighs the chances of taking over the current nest in the future versus the chances of founding or taking over another nest. A female’s fitness may also benefit more from guarding than leaving the nest. Ecological conditions will also affect a displaced female’s chances of starting a new nest.

Reproductive Suppresion
The dominant female of the nest suppresses reproduction of any other females in the nest by preventing them access to the cell in the tunnels of the nest necessary for eggs. The only way that another female in the nest can reproduce is if she takes over the nest by force, or leaves to either take over another nest or found her own.

Division of Labor
Labor is divided between guarding and foraging females. The foraging female is the reproductively dominant one, while the guarding females are either young pre-reproductive females or old formerly reproductive females. Young pre-productive females remain in the nest for up to two weeks. During this time they guard the entrance to the nest. This guarding is not their intended consequence however. Rather, this is how the progeny compete for food from the mother, as it is beneficial to be the first one at the entrance when the mother returns from foraging. They are fed by the mother via trophallaxis. Old formerly reproductive females become guards when a takeover of reproductive dominance in the nest occurs by a daughter or an outside intruder. The displaced female either remains in the nest as a guard or leaves in order to attempt to take over another nest. Nests that are guarded when the dominant female is out foraging are more reproductively productive, as more food collection is possible.

Foraging Behavior
X. pubescens cannot forge in temperatures below 18 degrees Celsius, likely due to the energy needed to maintain body heat for their large size. X. pubescens has been found to forage on 30 different plant species in India and 61 different species in Israel. It gathers both nectar and pollen from plants in the spring, summer and fall. In the winter, only nectar is gathered and foraging can only be accomplished on warm days. Mutualism is observed here, as the plant species pollinated by X. pubescens have been observed to low or zero fruit set rate if not pollinated but it. X. pubescens is also able to avoid revisiting plants on which it has already foraged by marking the plant with pheromones.

Mating Behavior
Breeding season is early March to early November. Most mating occurs in the spring but some still occurs in the fall. Mating is not yet well understood in X. pubescens. Males make territorial flights in shaded areas at a height ranging from a few centimeters to a few meters. These territories have been shown to be desirable by all males, as competition for them is common. In the case of an intruder, a male will charge the intruder to drive him away. If the intruder does not avoid the charging male, the charging male will bash the intruder with his head and will continue this pattern until the intruder is driven off. Females come into these male territories to mate but the mechanics are not yet known.

Predators
Ants of various species have been found to invade nests in some Xylocopa species. Additionally, because nesting takes place in wood, termites have been found to infiltrate nests, eat the walls, and fill it with refuse. Birds have also been observed to feed on X. pubescens, specifically the woodpecker species Dendrocopos syriacus in Mediterranean regions.

Parasites
Coelopencyrtus is an internal parasite of mature X. pubescens larvae, with hundreds emerging from each larvae. They run on top of X. pubescens nests constantly throughout nesting season, with activity peaking in the fall. Overwintering for Coelopencyrtus occurs in or near dead hosts.

Agriculture
Carpenter bees have been observed pollinating agricultural plants such as passionflower and cotton, but X. pubescens does not naturally pollinate any agricultural plants. However, in a greenhouse setting, X. pubescens has been shown to be a more effective pollinator of honeydew melon than honeybees. The obstacle for using X. pubescens for agricultural purposes is that a way to mass-rear them has not yet been developed.