Xylocopa sulcatipes

Taxonomy and phylogeny

X. sulcatipes is part of subfamily Xylocopinae within the hymenopteran family Apidae. Xylocopinae is divided into four tribes: Allodapini, Ceratinini, Xylocopini, and Manueliini. The genus Xylocopa, composed of large carpenter bees, consists of about 469 species in 31-51 subgenera. These species are distributed across the world. X. sulcatipes is part of the subgenus Ctenoxylocopa.

Description and identification

X. sulcatipes differs from other Arabian carpenter bees. Females are distinguishable by the presence of black pubescence -short matted hairs - on the face and the back side of the mesosoma.The mesoscutellum, or female middle body shield,does not extend over the metanotum, or middle thorax. Finally, the apical margin, the lower part of the abdomen, is rounded, as opposed to squared off. Lastly, they have a plate on their pygidium, their lowermost abdominal section.

Males are covered in a dark to black pubescence,with the exception of the face. The middle section, at the back, is mostly light or pale. The first metasomal tergum, or back, with subhorizontal dorsal surface rounds into the anterior surface.

X. sulcatipes eggs measure around 11 mm in length and 2.2 mm in diameter. Adults are approximately 22 mm in length.

Distribution and habitat

X. sulcatipes is a large Arabian carpenter bee. X. sulcatipes species has been found in Saudi Arabia, Yemen, Israel, Egypt, and Transcaspia.

X. sulcatipes are known to nest in cane or thin-branch nests. They use plants that are native to a particular region in order to build their nests; therefore, materials for nesting may vary. X. sulcatipes nests utilize dead branches, sticks, dead flowering stalks of Ferula spp., or other suitable soft, wooden, tubular objects, abandoned by human beings. The holes for their nest entrances are approximately 1.2 cm wide and the tunnels range from 1.2-1.6 cm wide. The tunnels are at least 12 cm long. The method in which X. sulcatipes construct their nests may vary. The female bee may cut a hole along the side of the nesting material, enter it, and then make the nest along the grain in one or both directions. They normally dig into substrate that needs little or no digging. Another way X. sulcatipes constructs its nest is by cutting into a pre-existing cut surface or broken cross-section. They will use this to gain entry into the substrate. After the structure of the nest has been formed, females linearly layer the walls with pollen and nectar and then put an egg into the food mass. Finally, the nest is sealed off.

The location of nests may vary from dead branches on the ground or cut wood that was hung above the ground; however, they are normally found in partially shaded areas.

Colony cycle

The nesting season starts early in the spring when males are looking for females to mate with. Some nests of X. sulcatipes may be matrifilial, where the line of descent is from mother to son. Other types of nests consist of sisters or unrelated females. Colonies may or may not have reproductive division of labor, which involves some of the reproductive females giving up reproducing in favor of the dominant female. This can occur after oophagy, which results from reproductive competition.

Nesting can either be metasocial or solitary. In a metasocial nest, there is more than one generation of bees occupying and cooperating within a nest. In solitary nesting, the founding bee forages, builds cells, lays the eggs, and guards. Normally only one generation of bees live in the nest. Nests can differ in how many female bees live in the nest for extended periods of time. If the nest only has one female living in it, the offspring of the founding mother take on some duties, such as guarding, after they are born and until they leave. Progeny normally leave about 1–2 weeks after emerging.

In other nests, there is more than one female that lives in the nest. In this type of nesting, multiple females either share in the foraging and nest laying, or one female does all the foraging and nest laying, while the other females guard.

Ontogeny

X. sulcatipes eggs are laid in closed cells that are prepared within 1–3 days. Preparation includes pollen gathering and bee-breading. When the eggs hatch, the small larva feed on the bee-bread while remaining in the same position. A few days afterwards, the larva begin to move and molt. This second instar takes various positions on the bee-bread. The second molt is followed by deposition of meconia and exhaustion of the bee-bread supply. Next, the pre-pupal stage starts. This stage lasts several days and ends in pupation. The pupae start out white and get darker with time. The gap in hatching between the youngest and oldest bees increases when the nest gets larger. After the bees hatch, they stay in the nest for some time. While in the nest, the bees do not harm the unhatched bees and are fed by the mother. Once all the bees have hatched, they clear the tunnel of all the broken down partitions and meconia. The mother stays with her offspring until they are independent. Only after this does the mother bee start building new cells.

Kin selection

X. sulcatipes are known to take part in altruistic behavior. These behaviors may be attributed to guarding, and the concessions received from undisturbed broods. A benefit from partaking in such a behavior where the guards are related to the mother bee is that this increases the bee's indirect fitness when they help kin because that helps propagate some small portion of the bee's genes. The guarding behavior of X. sulcatipes is similar to that of Xylocopa pubescens. However, unrelated guards don't receive much genetic gain. This is because unrelated workers that help guard do not share any common genes with the queen whom is the breeder, and therefore can't pass on genes they share in common.

Seasonal activity

In order for X. sulcatipes to partake in flight, they first need to raise their muscular temperature to 37 °C. However, in order to maintain flight activity, these bees need to be at a threshold temperature of around 21 °C. Warmer days in the winter trigger X. sulcatipes to eat more of their food supply. While these bees don't normally fly around in the winter, the frequency of flights they take during the cold season results from how many warm winter days there are. When the weather starts getting warmer, these bees begin making more flights. During May, night temperatures reach 21 °C so X. sulcatipes can start flying out at dawn, which is earlier than the previous months. Typically, these bees stop flying shortly after sunset.

X. sulcatipes nest and lay their eggs in the spring and summer. They are normally not active during the winter months and they partake in minimal activities to sustain life. During these winter months, the bees fly around in search of nectar on warm days. These little trips give the bees just enough nectar and energy to make more trips on warm days during this cold season.

Territorial behavior

Males of the species X. sulcatipes are known to mark and defend their territories by secreting chemicals from their mandibular glands. Chemical analysis has shown that the secretions are composed of p-cresol, guaiacol, and vanillin. Territorial males defend their territories either by identifying intruding males through site or recognizing the distinct odor the encroaching male emits from its mandibular glands. If the visitor is a female it is not chased out. Sometimes, however, if a reconstituted pheromonal secretion is treated to the female, it is dealt with as if it were a male and chased out of the territory.

Other territorial behaviors include the flight of males from one nest to another, aggregating in a mass around flowering trees where each male defends a small section of the area around the tree. Males will also cruise and defend their own plant or plants. Another behavior includes a massive flight of males flying around the canes that females nest in. Males defend areas around nesting sites and food resources. The territorial mechanism used depends on what is being defended and the location. For example, if flowers that females feed on are more dispersed and close to their nesting sites, males may defend their own flower or flowers as a strategy.

Mating behavior

X. sulcatipes males chase after anything that is approximately their own size. If this object happens to be a female, the male will follow the female to the flower she is seeking. He will fly over her with his antennae outstretched above her abdomen. If the female wants to mate, she will spread her wings and release an odor from her mandibular glands. This secretion is a signal to the male and he continues to hover over her until she leaves the flower. As the female flies off the flower, the male grasps her in the air, and they fly some distance and try to copulate. While copulating, the male is turned 60° to the female. Many times the male will follow the female after copulation.

Resource defense polygyny

Because males defend areas near nesting or flowering sites, female and/or resource defense polygyny is common. Resource defense polygyny is when males acquire females by taking control of limited resources such as food and nesting sites. Females can gain access to these resources by mating with the males that defend these territories. Males can copulate with the best mate by defending the best resource because females are more attracted to these better resources. Therefore, the male will mate with multiple females that come to use the resources that the male is defending.

Nesting behavior

At night, most bees are asleep while some are still active. A common sleeping position for X. sulcatipes is they lay on their dorsum with their face turned upward on top of a pollen slant. A female in the nest will spend much of her time licking the walls of the nest tunnels or the walls where she is about to build a new nest. Also they will tap the walls of the tunnel with their abdomen, which secretes chemicals. X. sulcatipes have also been found to walk around with their sting-chamber open. This behavior is attributed to having to do with the release of contents from glands that open from the chamber. The secretions coat the walls of the nest with a thin, transparent film.

Routinely, only minor cleanings are done in the nest. Major nest cleanings take place during and right after excavation of tunnels. It also takes place after all the offspring have hatched. Pupal skins, broken cell partitions, meconia, and the remains of cells where development has stopped are thrown out. There is no need to remove defecation from adult bees because this takes place outside the entrance hole or away from the nest.

Defense

In nest defense, there is competition among conspecific females for nesting sites. As the population of X. sulcatipes increases in a region, competition also increases. This increase in competition results in intensive guarding of nests, especially in the spring and summer when it is prime nesting season. Nest guarding can be against bees of the same species or against those of other species.

Parasites

Nests of X. sulcatipes have been found to be invaded by termites, in particular nests on Ferula plants in the deserts around Sede-Boqer. Once the termites get into the nest, they take apart the walls and fill it with refuse. The bees may respond by stopping the digging of tunnels once they have any inclination of termite damage.

Predators

Other insects may also pose a threat to these bees, e.g., a female praying mantis (Sphodromantis viridis) was observed catching and eating a male X. sulcatipes.

Diet

X. sulcatipes visits flowers for both pollen and nectar collection. In the Arava Valley, Calotropis procera, Retama raetam, Acacia tortilis, and A. raddianna are native plants most commonly visited by this bee. Depending on the season of the year, certain plants are preferred. For example, C. procera, only gives nectar to the bees and blooms from March to September, so only during these months do X. sulcatipes visit this plant species. This flower is very popular among the bees. Retama raetam blooms for only a short period of time from March to April. The way this bee species collects nectar is by settling on a flower and inserting its proboscis. X. sulcatipes mixes the nectar and pollen it gathers at irregular intervals and thus, there is great variability in bee bread sizes. This leads to different adult bee sizes.

Interactions with humans

Plant species cultivated for human consumption are commonly visited by X. sulcatipes for their nectar and pollen.In the Arava Valley, these include Cassia spp., Lucaena glauca, Solanum elaeagnifolium, and Vitex agnus-castus.