Xylocopa pubescens
Xylocopa pubescens is a species of large carpenter bee. Females form nests by excavation with their mandibles, often in dead or soft wood. X. pubescens is commonly found in areas extending from India to Northeast and West Africa. It must reside in these warm climates because it requires a minimum ambient temperature of in order to forage.
A common area of study in X. pubescens is its dominance hierarchy and guarding behavior. Colonies start and end with female takeover, either by daughters of the dominant female or by foreign intruders. There is only one reproductively active female in a colony at a time who suppresses the reproduction of other females in the nest. Males hold individual territories which females enter to mate. When an intruder enters another male's territory, the male responds aggressively.
X. pubescens is polylectic, so it forages on many species of plants. It forages on some plants for nectar when preparing bee bread during ontogenesis and forages on others for pollen to feed offspring. Pheromones from Dufour's gland are vital to mark flowers previously visited and also to mark nests so that the foraging bees know where to return. X. pubescens is known to be an effective pollinator, often more effective than honeybees, but it is not commonly used in today's agricultural settings.
Taxonomy and phylogeny
Xylocopa pubescens is in the order Hymenoptera, and in the family Apidae, which is a large bee family. X. pubescens belongs to the Xylocopa 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. Koptortosoma is polyphyletic and constitutes a sister lineage of Mesotrichia. 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. 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. 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 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.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-reproductive 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. The mother feeds them 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 reproduction, as more food collection is possible.Behavior
Foraging behavior
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. Mutualism is observed between X. pubescens and several species of plants, as the species pollinated by X. pubescens have been observed to have low or zero fruit set rate if not pollinated by it. X. pubescens is also able to avoid revisiting plants on which it has already foraged by marking the plant with pheromones.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. X. pubescens will adjust foraging behavior accordingly. Most flower visits are short, lasting from about 4 seconds to 8.5 seconds.Plants by region
In India plants visited by X. pubescens for pollen are Cochlospermum religiosum, as well as Peltophorum, Cassia and Solanum species. Those visited for nectar include Calotropis, Bauhinia, Crotalaria, Anisomeles, and Gmelina species and some other plants.In the Mediterranean the most common plants visited by X. pubescens for both pollen and nectar are Helianthus annuus, Parkinsonia aculeate, Luffa aegyptiaca, as well as Lonicera species.
In Israel, the ranges of X. pubescens and X. sulcatipes overlap, leading to competition between the two species for plants to forage on. Both species visit Calotropis procera only for nectar, Retama raetam for both pollen and nectar, and Lucaena only for pollen. Because X. pubescens has a minimum ambient temperature for activity of about while X. sulcatipes has a minimum ambient temperature of, X. pubescens can begin foraging earlier in the day than X. sulcatipes. This allows X. pubescens to get to flowers first, but then after X. sulcatipes begins foraging, it becomes the dominant bee. The bees can recognize when a flower has been previously visited by a bee of either species, and will proceed to avoid that flower.