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Simple Summary: Explanations for the evolution of menopause in humans and other animals concern the indirect fitness benefits that older females can receive by caring for the offspring of their children and grandchildren. Knowledge about the post-reproductive lifespan is still incomplete and until recently was documented only in nonhuman primates, a few species of toothed whales, and guppies, though it has also been documented in insects for gall-forming aphids and parthenogenetic ants. In our paper, we provide evidence that menopause also exists in honeybee societies. Honeybee workers are usually sterile. Nevertheless, the absence of a queen and her pheromones in a nest stimulates workers to activate their ovaries and lay unfertilized eggs that develop into males. However, even in queenless colonies, some workers do not activate their ovaries. In this study, we show that physiologically older workers have less activated ovaries than physiologically younger individuals, indicating that the possibility of workers' reproduction decreases with workers' physiological age. This may happen because bees require a minimum of two weeks to activate their ovaries, meaning physiologically older workers can die before producing their own eggs. Thus, investing energy in helping relatives care for their offspring rather than channelling that energy into one's own reproduction can positively influence workers' fitness. The post-reproductive lifespan is an evolutionary enigma because the cessation of reproduction in animals seems contrary to the maximization of Darwinian fitness. Several theories aim to explain the evolution of menopause, one of which suggests that females of a certain age receive more fitness benefits via indirect selection (kin selection) than they would directly from continuing reproduction. Post-reproductive lifespans are not very common in nature but have been described in humans, nonhuman primates, a few species of toothed whales, guppies, and in some insect societies consisting of clonal colony members, such as aphid and ant societies. Here, we provide evidence that menopause also exists in honeybee societies. Our study shows that workers with a short life expectancy (older and/or injured workers) invest fewer resources and less time in their own reproduction than workers with a long life expectancy (younger and/or uninjured workers), even if their colony is hopelessly queenless. These results are consistent with the kin selection explanation for the evolution of menopause and help us understand the net effects of relatedness and social cooperation in animals. [ABSTRACT FROM AUTHOR]

Worker honeybees may reproduce in either their own or foreign colonies; the latter situation is termed intraspecific reproductive parasitism (IRP). In this study, we compared the tendency for IRP between normal honeybee workers, which are characterized by a relatively low reproductive potential, and "rebel workers", a recently discovered subcaste of honeybee workers characterized by a high reproductive potential that develops when the colony is without a queen. We expected that the high reproductive potential of the rebel workers would influence their reproductive strategy and that these individuals would drift to other colonies to lay eggs more often than normal workers. The results confirm our expectations and show that rebel workers are more likely than normal workers to drift to foreign colonies. The rebel workers also preferred to drift to queenless colonies than to queenright colonies, while the normal workers did not show this preference. This study indicates that rebel workers have a tendency for IRP, which may be responsible for the maintenance of the rebel worker strategy in bee populations. In this article we find that new subcaste of honeybee workers can be intraspecific parasites. These individuals drift to other colonies and activated their ovaries. [ABSTRACT FROM AUTHOR]

In the honeybee, diploid larvae fed with royal jelly develop into reproductive queens, whereas larvae fed with royal jelly for three days only and subsequently with honey and pollen develop into facultatively sterile workers. A recent study showed that worker larvae fed in a queenless colony develop into another female polyphenic form: rebel workers. These rebel workers are more queenlike and have greater reproductive potential than normal workers. However, it was unclear whether larvae orphaned at any time during their feeding period can develop into rebels. To answer this question, the anatomical features of newly emerged workers reared in queenless conditions at different ages during the larval period were evaluated. Our results showed that larvae orphaned during the final four or more days of their feeding life develop into rebel workers with more ovarioles in their ovaries, smaller hypopharyngeal glands, and larger mandibular and Dufour’s glands compared with typical workers with low reproductive potential that were reared with a queen or orphaned at the third to last or a later day of feeding life. [ABSTRACT FROM AUTHOR]

Researchers in many fields would like to understand the determinants of risk-taking. Social insects are an excellent model for examining them since the tasks they perform bear different risks. Some honeybee ( Apis mellifera) workers do not forage for nectar or pollen; instead, they take on the extreme risk of robbing honey from other bee nests. In this paper, we show that robbers live shorter lives than foragers under the same cage conditions, and that they are more often and more heavily infected with the intestinal parasite Nosema than foragers are. This finding supports the theoretical prediction that risky tasks should be undertaken by shorter-lived individuals. [ABSTRACT FROM AUTHOR]

Under the age-related division of labour of a honeybee colony, workers participate first in safe inside-nest tasks and then switch to risky outside-nest foraging. However, honeybees show great plasticity during behavioural development: their hive-to-field transition can be accelerated, delayed or even reversed in response to changes in colony conditions or environmental factors. After nursing bees are removed from a colony, younger foragers are more likely to revert to nursing than older ones. The ‘division of labour by division of risk’ hypothesis predicts that it is not the workers'' age but their life expectancy that influences whether or not foragers return to inside-nest activity. We tested this prediction by dividing same-age honeybee workers into three groups after they started foraging. Workers in the control group were not treated. The life expectancy of the other two groups was shortened with carbon dioxide anaesthesia or by injury. In a cage experiment we showed that control bees had a longer expected life span than anaesthetized and injured workers, while in a field experiment the control workers, with a longer expected life span, proved more likely to revert to nursing than anaesthetized and injured workers of the same age. Behavioural reversion was accompanied by ovary development and hypertrophy of the hypopharyngeal glands. These results support the tested hypothesis that the division of labour in eusocial insects is a consequence of differences in expected worker life span and differences in the risks associated with inside-nest and outside-nest tasks. [Copyright &y& Elsevier]

Nests of social insects are usually inhabited by various mite species that feed on pollen, other micro-arthropods or are parasitic. Well-known negative effects of worldwide economic importance are caused by mites parasitizing honeybee colonies. Lately, attention has focused on the endoparasitic mite Locustacarus buchneri that has been found in commercial bumblebees. However, little is known of other mites associated with commercial bumblebee nests. Transportation of commercial bumblebee colonies with unwanted residents may introduce foreign mite species to new localities. In this study, we assessed the prevalence and species composition of mites associated with commercial bumblebee nests and determined if the mites are foreign species for Poland and for Europe. The study was conducted on 37 commercial bumblebee nests from two companies (Dutch and Israeli), originating from two greenhouses in southern Poland, and on 20 commercial bumblebee colonies obtained directly from suppliers. The species composition and abundance of mites inhabiting commercial bumblebee nests were determined. Seven mite species from three families were found in nests after greenhouse exploitation. The predominant mite species was Tyrophagus putrescentiae (Acaridae) that was a 100-fold more numerous than representatives of the family Laelapidae ( Hypoaspis marginepilosa, H. hyatti, H. bombicolens). Representatives of Parasitidae ( Parasitellus fucorum, P. crinitus, P. ignotus) were least numerous . All identified mite species are common throughout Europe, foreign species were not found. Mites were not detected in nests obtained directly from suppliers. We conclude that probably bumblebee nests are invaded by local mite species during greenhouse exploitation. [ABSTRACT FROM AUTHOR]

Bee pollinators are currently recorded with many different sampling methods. However, the relative performances of these methods have not been systematically evaluated and compared. In response to the strong need to record ongoing shifts in pollinator diversity and abundance, global and regional pollinator initiatives must adopt standardized sampling protocols when developing large-scale and long-term monitoring schemes. We systematically evaluated the performance of six sampling methods (observation plots, pan traps, standardized and variable transect walks, trap nests with reed internodes or paper tubes) that are commonly used across a wide range of geographical regions in Europe and in two habitat types (agricultural and seminatural). We focused on bees since they represent the most important pollinator group worldwide. Several characteristics of the methods were considered in order to evaluate their performance in assessing bee diversity: sample coverage, observed species richness, species richness estimators, collector biases (identified by subunit-based rarefaction curves), species composition of the samples, and the indication of overall bee species richness (estimated from combined total samples). The most efficient method in all geographical regions, in both the agricultural and seminatural habitats, was the pan trap method. It had the highest sample coverage, collected the highest number of species, showed negligible collector bias, detected similar species as the transect methods, and was the best indicator of overall bee species richness. The transect methods were also relatively efficient, but they had a significant collector bias. The observation plots showed poor performance. As trap nests are restricted to cavity-nesting bee species, they had a naturally low sample coverage. However, both trap nest types detected additional species that were not recorded by any of the other methods. For large-scale and long-term monitoring schemes with surveyors with different experience levels, we recommend pan traps as the most efficient, unbiased, and cost-effective method for sampling bee diversity. Trap nests with reed internodes could be used as a complementary sampling method to maximize the numbers of collected species. Transect walks are the principal method for detailed studies focusing on plant-pollinator associations. Moreover, they can be used in monitoring schemes after training the surveyors to standardize their collection skills. [ABSTRACT FROM AUTHOR]

Workers present in the colony of social insects differ in age. The strategy of engaging younger workers in safer intranidal tasks, and older individuals in riskier tasks, for example, foraging, increases the average longevity of workers, and thus colony fitness. The transition to becoming a forager can be influenced by many environmental and social factors, but it has remained unclear whether the onset of foraging is also directly dependent on life expectancy. We tested this hypothesis with laboratory colonies of the ant Myrmica scabrinodis by creating groups of workers with reduced life expectancy. Ants were either anaesthetized with carbon dioxide or injured by removing their propodeal spines. Both treatments significantly shortened worker life expectancy in comparison to untreated control workers. Next, we showed that workers with an experimentally reduced life span became foragers earlier in life than control workers. This implies that ant workers adjust their threshold for engaging in risky foraging according to their life expectancy. [Copyright &y& Elsevier]

Social insects, especially honeybees, have received much attention in comparative gerontology because of their peculiar and flexible ageing patterns that differ across genetically similar individuals. The longevity of honeybee individuals varies and depends on patterns of gene expression during development; females developing into reproductive individuals (queens) live longer than facultatively sterile workers. Here, we show that rebel workers, which develop under queenless conditions after swarming and have high reproductive potential, live approximately 4 days longer in hives and approximately 3 days longer in cages than individuals that develop in queenright colonies and have lower reproductive potential; this difference in longevity occurs in both free-flying and caged workers. Moreover, we show that both rebel and normal workers live longer when their ovaries contain more ovarioles. Longer-living rebel workers can benefit the colony because they can fill the generation gap that emerges between workers after queen exchange during swarming. Our findings provide novel evidence that the fecundity of workers in a social insect colony impacts their intrinsic longevity. [ABSTRACT FROM AUTHOR]