Red mason bee

Appearance

''O. bicornis'' is about the same body size as the honeybee. Sexual dimorphism is observed in this species; females are larger than males, because the female larvae are provisioned with more pollen. Body size in ''O. bicornis'' decreases as temperature in brood cells increases. Beyond 25 °C, body growth can be severely truncated, leading to small adult body size or mortality. The male and females are also distinguishable by antenna length, with males possessing an additional antenna segment, .

Distribution

''O. bicornis'' is found in England, southern Scotland , Wales, Ireland, mainland Europe, Sweden, Norway, North Africa, Georgia, Turkey, and Iran. Of the 11 species identified of ''Osmia'' in England, ''O. bicornis'' is both the largest and most common species present.

''O. bicornis'' occupies a variety of nesting sites within nature and in sites of human construction. These bees have been known to nest in key holes, empty snail shells, plant stems, and empty beetle hollows. ''O. bicornis'' occupies the old shells of these three species: ''Helix nemoralis'', ''Helix hortensis'', and ''Helix pomatia'' and the nests of ''Anthophora'' species. Additionally, these bees make their nests in such sites as sandy banks, decaying trees planted in clay soil like the willow tree, old-mortared walls, flint stone holes, garden shed fifes, and window frame holes and cracks.

The maximum foraging distance for ''O. bicornis'' is about 600 m, though generally high plant density around the nests allow bees to forage closer to the nest and for a shorter duration.

Behavior

During mating season, male behavior with respect to pursuing females is varied, with some males establishing territories close to nesting sites where females emerge and other males observing flowering sites nearby. Males do not normally engage in intrasexual aggression, though they do inspect each other. When a specific mate of interest is present, however, signs of aggression are evident among males. When several males become aware of a receptive female, all males try to mount her; the males do not assault each other directly. In some cases, females may escape and not mate with any of the males.

Females are monogamous, mating with one male within a few days after emergence in the spring. However, males encounter difficulties in completing successful copulation with females, including male inability to determine from where and when females will emerge. Nests are dispersed widely, increasing the number of sites from which new females can emerge. Additionally, females fly away from the nests as soon as they emerge, increasing the mating challenge for males. To counteract these difficulties, males can increase their mating chances by positioning themselves close to foraging sites. Factors including value, patrolling time, and the number of competing males are taken into account when males roam foraging sites for females.

In male-female interactions, males sense potential mates by observing the body shape of females, and by evaluating the female's sense, determine whether a specific female will be receptive to copulation. Females use such cues as the vibrational bursts of the male thorax, which has been suggested to be a sign of male health and overall fitness, color, and odor to select mates. Successful mating of females does not depend on male body size, but on the speed with which males discover female mates. Further, females do not always choose the male with the largest body size, a choice that possibly indicates a preference exists for an optimum male body size; often, females choose males with intermediate body sizes. Yet, the sperm supply of each male limits males to only performing seven copulations in their lifetimes.

Food

Females spend between 80 and 95% of their time invested for preparing cells in foraging. ''O. bicornis'' has shown a strong inclination towards collecting pollen from maple and oak trees, like most other solitary bees. These bees require nectar along with pollen, and while maple provides both, oak provides only pollen. Those females that collect pollen from oak trees must also collect nectar from other plant sources. While the species is polylectic, females temporarily and locally forage on one or two plant species with great pollen abundance to maximize pollen mass collected per unit time. This is done to reduce provisioning time to exploit as much pollen as possible in a short period of time during unstable environmental conditions in the spring and to reduce the risk of open-cell parasitism. Pollen diversity has shown no effect on the developmental success of ''O. bicornis'' offspring, hence it is more beneficial for females to maximize pollen mass from a few species than to regard pollen diversity. Protein consumption is one of the major factors influencing the growth of bees. Since maple and oak pollen have similar protein content , larvae reared on the diet of either plant do not differ in cocoon weight – hence the offspring of ''O. bicornis'' develop equally on the pollen of both zoophilous and anemophilous plants. When oak and maple are no longer in bloom, the bees tend to forage on pollen from poppy and buttercup plants.

Environmental temperature and cocoon weight are negatively related for ''O. bicornis''. Larvae decrease their food intake as temperature rises and start cocoon-spinning earlier, resulting in smaller body mass.''O. bicornis'' feeds on pollen, the amount of which affects larval growth. A majority of the pollen these bees consume comes from ''Ranunculus acris'', ''R. bulbosus'', ''R. repens'', and ''Quercus robur'' flowering species. Pollen consumption has also been suggested to impact the fitness of individuals in the colony. These bees also consume nectar. When the nectar supply is limited, however, they may consume honeydew.

Defense

Normally, ''O. bicornis'' does not sting unless it is threatened and must defend itself. The female does have a sting, but it is much less severe than honeybees or wasps. The venom within the stinging apparatus has been shown to be like that of the honeybee. However, venom apparatus from ''O. bicornis'' contains fewer barbs than that of honeybees, possibly explaining why ''O. bicornis'' venom does not penetrate human skin like that of the honeybee. Protein components in the venom, such as osmin, have been linked to antimicrobial, antifungal, and haemolytic activities.

Cultural

Red mason bees are excellent pollinators, particularly of apple trees. For effective use of these bees as pollinators of winter rape plantations in Poland, they should be located at least 300 m from entomophilous plants, which distract the bees from pollinating the plants of interest.