Xylocopa pubescens

Xylocopa pubescens is in the order Hymenoptera, and in the family Apidae, which is a large bee family. X. pubescens belongs to the Xylocopa ("wood chopper") genus, a genus composed of over 400 species of large carpenter bees. It has sometimes been treated as a subspecies of X. aestuans, though most commonly considered a distinct species. It is a member of the subgenus Koptortosoma, which is the largest Xylocopa subgenus and is widely distributed with over 200 species. In scientific Greek, Xylocopa pubescens literally means "wood chopper covered with hairs". == Description ==

Females are large and shiny, black with yellow markings on their heads. Males are smaller than females, distinguished by a narrow head and yellow pubescence that covers their entire bodies. == Distribution and habitat ==

Range X. pubescens has been found throughout the Eastern Mediterranean Basin, North Africa and the Middle East. It ranges from Cape Verde to South Asia. It recently expanded its distribution to Spain and Greece in Europe. The species tends to inhabit these relatively warm areas as it requires a minimum temperature of 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 diameter; a widened entryway leads into a chamber that is . Tunnels in diameter start at the chamber, follow grain, and are long, consisting of few cells each. Females enlarge nests by digging new tunnels when progeny are in the late larval or pupal stages. 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 each cycle. == 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. Each colony is founded by a solitary female. The 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 enters the pupal stage. After that, between 1–8 adult females may be present 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. 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. Abdominal glands in females are white when they are young and grow more yellow as they mature. Total developmental time from egg to adult is around 45–49 days, lasting somewhat less in the summer. == Dominance hierarchy ==

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. The dominant female must then determine whether or not she will allow the defeated female to remain as a guard. Factors such as age and relatedness play into this decision. A deposed female guard who is young is likely to attempt a takeover of the nest in the future, as is one who is not closely related to the current dominant female. Reproductive output has been shown, however, to increase in guarded nests. If the defeated female is allowed to remain, she too must decide whether or not to do so. This decision depends on 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 suppression Reproductive suppression is often used in social insect colonies by queens to maintain a genetic monopoly of the offspring in the nest. Some species suppress worker egg laying through pheromones and chemical control. However, in Xylocopa pubescens, 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. ==Behavior==

Foraging behavior on basil. Note symbiotic mite on its back.|alt=Female foraging on basil flowers. A symbiotic mite is visible on its back. X. pubescens cannot forage in temperatures below , 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. Plant visitation X. pubescens is a polylectic bee, meaning it visits many different species of plants. Flower color impacts visitation, and yellow flowers or white flowers that are creamy, purplish, or bluish are preferred. Scent is also an important factor, as most nectar-producing plants visited by X. pubescens have a strong odor to attract bees and insects. As X. pubescens is a large carpenter bee, it prefers medium to large size flowers. Zygomorphic flowers with bilateral symmetry are also preferable. Plants only produce nectar and/or pollen at certain times of the day, while balancing sugar and water amounts in the nectar for foraging bees. Examples of different anthesis schedules are late at night for Careya arborea, the afternoon in Crotalaria species, and all day in Calotropis species. 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 (inches to yards). 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 of how this works are not yet known. The benefits of guarding behavior can clearly be seen here as strangers hardly ever intrude on social nests containing more than one adult. == Exocrinology and communication ==

X. pubescens have glands that are vital in their exocrine system and play a large part in communication. One category of glands is the intersegmental glands, also known as the yellow glands. The intersegmental glands are made up of several gland pairs in the abdomen, which open up into the intersegmental membranes. These glands distinguish non-nesting bees from bees that are actively breeding. In non-nesting bees they are compact and white. They increase in size and turn from white to yellow as breeding season progresses. Unicellular secretory elements in these glands empty through a duct into the intersegmental membranes, from which the chemicals are released. The other important glands, especially for communication, is the Dufour's gland. The original role of these glands in various bee species was to produce the brood cell lining, but this function does not exist in Xylocopa species. Instead, these glands are responsible for the production of scent marking pheromones. These are strictly hydrocarbons in X. pubescens, and are used to mark flowers that have been previously visiting on foraging trips in order to avoid them. These scent markings on previously visited flowers are recognized both by X. pubescens and X. sulcatipes, which allows the two species to be more efficient in foraging. This system of scent marking is also involved in nest recognition. == Interactions with other species ==

Predators Ants of various species have been found to invade nests in some Xylocopa species, specifically, Monomorium gracillimum. The ants dig small holes in the tunnel walls of X. pubescens to get into the nest. No confrontation occurs, as the mother attempts to remove as many of her brood as she can before the destruction of the nest and all brood cells. 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 Wasps in the genus Coelopencyrtus are internal parasitoids of mature X. pubescens larvae, with hundreds emerging from each larva. 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 do not naturally pollinate any agricultural plants. However, in a greenhouse setting, X. pubescens have been shown to be a more effective pollinator of honeydew melon than honeybees by increasing the fruit set three times more than a honeybee. The obstacle for using X. pubescens for agricultural purposes is that ways to mass-rear them have not yet been developed. == References ==