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The queen mandibular pheromone (QMP) identified from the honeybee is responsible for maintaining reproductive division of labour in the colony, and affects multiple behaviours. Interestingly, QMP inhibits reproduction not only in honeybee workers, but also in distantly related insect species such as fruit flies and bumblebees. This study examines whether QMP also affects worker reproduction in the common wasp Vespula vulgaris. Wasp workers were exposed to one of the following treatments: QMP, wasp queen pheromone (the hydrocarbon heptacosane n-C27), or acetone (solvent-only control). After dissecting the workers, no evidence that QMP inhibits development in V. vulgaris could be found. However, this study could confirm the inhibitory effect of the hydrocarbon heptacosane on ovary activation. The reason why non-social species such as the fruit fly and social species such as bumblebees and ants respond to the QMP, while the social wasp V. vulgaris does not, is unclear. The investigation of whether olfaction is key to sensing QMP in other insect species, and the detailed study of odorant receptors in other social insects, may provide insights into the mechanisms of response to this pheromone. [ABSTRACT FROM AUTHOR]

Chemical signals are known to play an important part in the organisation of insect societies, but the mode of action of these signals is still a subject of controversy. While some researchers propose that pheromones produced by the queen are honest signals of her quality informing worker behaviour, others suggest that they are means of manipulation not necessarily beneficial to workers' fitness. The honeybee (Apis mellifera) is sometimes cited as an example of the latter possibility. Our study aimed to test the extent to which queen quality predicts worker behaviour, the relation of queen-produced chemicals to her quality and the interplay between queen signalling and worker behaviour. We decided to test worker attitude towards different queens in the most direct way by presenting groups of workers simultaneously with two different queens of differential reproductive capacity, and analysing worker behaviour towards each of them in terms of attendance, retinue and aggression. Our results indicate that workers show preference for queens with higher reproductive potential, that queen's reproductive potential was honestly reflected in queen-produced signals and that these signals indeed guide worker behaviour. Thus, our findings overall support the honest queen signal theory and contribute to understanding of mechanisms underlying different phenomena in bee sociality. [ABSTRACT FROM AUTHOR]

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Animal nutritional state can profoundly affect behaviour, including an individual's tendency to cooperate with others. We investigated how nutritional restriction at different life stages affects cooperative behaviour in a highly social species, Apis mellifera honeybees.We found that nutritional restriction affects a worker's queen pheromone response, a behavioural indicator of investment in group vs. individual reproduction. Nutritional restriction at the larval stage led to reduced ovary size and increased queen pheromone response, whereas nutritional restriction at the adult stage led to reduced lipid stores and reduced queen pheromone response.We argue that these differences depend upon the extent of reproductive plasticity at these life stages and that individual worker honeybees may adjust their behavioural and physiological traits in response to nutritional stress to invest nutritional resources in either their own or their colony's reproduction.These results support the role of nutritional stress in the maintenance of cooperative behaviour, and we suggest that historical nutritional scarcity may be an important contributor to the evolution of extreme forms of cooperation. A plain language summary is available for this article. Plain Language Summary [ABSTRACT FROM AUTHOR]

To test the hypothesis that exposure to queen mandibular pheromone (QMP) modulates ecdysteroid production in adult worker honey bees, ecdysteroids were measured in hemolymph and other tissues of individual adult worker honey bees reared with or without QMP in cages and field colonies. Ecdysteroid titers were higher in caged workers exposed to QMP continuously from the first day of adult life than in workers reared without QMP. Statistical cluster analysis suggested the possibility that a subgroup of workers (“responders”) is more sensitive to QMP in this regard than other workers. In 12-day-old workers, ecdysteroid titers in workers reared in queenright (QR) colonies were similar to those observed in cages with QMP, but lower than those in queenless (QL) colonies. Differences in number of ovarioles or degree of ovarian activation did not correlate with hemolymph ecdysteroids. Previous studies have demonstrated ecdysteroids in hemolymph in very young adult workers and in workers in QL colonies; the present study indicates that production of ecdysteroids occurs in older adult worker honey bees in the absence of morphological signs of ovarian activation, with cage studies revealing a modulatory role for QMP masked in the complex environment of the hive. [ABSTRACT FROM AUTHOR]

In social insect colonies the presence of a queen, secreting her pheromones, is a key environmental cue for regulating the reproductive state of workers. However, until recently the proximate molecular mechanisms underlying facultative worker sterility were unidentified. Studies into worker oogenesis in the honey bee ( Apis mellifera) have indicated that programmed cell death is central to the regulation of oogenesis. Here we investigate how queen pheromone, age of the worker and ovary state affect both programmed cell death and cell number in worker ovaries. We describe a novel method to simultaneously measure programmed cell death (caspase activity) and live cell number (estimated from the amount of adenosine triphosphate) in an insect tissue. Workers exposed to queen pheromone have higher levels of caspase activity in the ovary than those not exposed. Our results suggest that queen pheromone triggers programmed cell death at the mid-oogenesis checkpoint causing the abortion of worker oocytes and reproductive inhibition of the worker caste. Nonetheless, high caspase activity is present in activated ovaries from workers not exposed to queen pheromone. This caspase activity is most likely to be from the nurse cells undergoing programmed cell death, in late oogenesis, for normal oocyte development. Our study shows that the social environment of an organism can influence programmed cell death within a tissue. [ABSTRACT FROM AUTHOR]

Several insect pheromones are multifunctional and have both releaser and primer effects. In honey bees ( Apis mellifera), the queen mandibular pheromone (QMP) and e-beta-ocimene (eβ), emitted by young worker larvae, have such dual effects. There is increasing evidence that these multifunctional pheromones profoundly shape honey bee colony dynamics by influencing cooperative brood care, a fundamental aspect of eusocial insect behavior. Both QMP and eβ have been shown to affect worker physiology and behavior, but it has not yet been determined if these two key pheromones have interactive effects on hypopharyngeal gland (HPG) development, actively used in caring of larvae, and ovary activation, a component of worker reproductive physiology. Experimental results demonstrate that both QMP and eβ significantly suppress ovary activation compared to controls but that the larval pheromone is more effective than QMP. The underlying reproductive anatomy (total ovarioles) of workers influenced HPG development and ovary activation, so that worker bees with more ovarioles were less responsive to suppression of ovary activation by QMP. These bees were more likely to develop their HPG and have activated ovaries in the presence of eβ, providing additional links between nursing and reproductive physiology in support of the reproductive ground plan hypothesis. [ABSTRACT FROM AUTHOR]

The presence of the honey bee queen reduces worker ovary activation. When the queen is healthy and fecund, this is interpreted as an adaptive response as workers can gain fitness from helping the queen raise additional offspring, their sisters. However, when the queen is absent, workers activate their ovaries and lay unfertilized eggs that become males. Queen pheromones are recognised as a factor affecting worker ovary activation. Recent work has shown that queen mandibular pheromone composition changes with queen mating condition and workers show different behavioural responses to pheromone extracts from these queens. Here, we tested whether workers reared in colonies with queens of different mating condition varied in level of ovary activation. We also examined the changes in the chemical composition of the queen mandibular glands to determine if the pheromone blend varied among the queens. We found that the workers activated their ovaries when queens were unmated and had lower ovary activation when raised with mated queens, suggesting that workers detect and respond adaptively to queens of differing mating status. Moreover, variation in queen mandibular gland's chemical composition correlated with the levels of worker ovary activation. Although correlative, this evidence suggests that queen pheromone may act as a signal of queen mating condition for workers, in response to which they alter their level of ovary activation. [ABSTRACT FROM AUTHOR]

The discovery of 'queen substance', and the subsequent identification and synthesis of key components of queen mandibular pheromone, has been of significant importance to beekeepers and to the beekeeping industry. Fifty years on, there is greater appreciation of the importance and complexity of queen pheromones, but many mysteries remain about the mechanisms through which pheromones operate. The discovery of sex pheromone communication in moths occurred within the same time period, but in this case, intense pressure to find better means of pest management resulted in a remarkable focusing of research activity on understanding pheromone detection mechanisms and the central processing of pheromone signals in the moth. We can benefit from this work and here, studies on moths are used to highlight some of the gaps in our knowledge of pheromone communication in bees. A better understanding of pheromone communication in honey bees promises improved strategies for the successful management of these extraordinary animals. [ABSTRACT FROM AUTHOR]

To explore reasons for the unusually high rates of worker ovary activation in Apis cerana, we investigated the reproductive physiology of workers in conspecific and mixed-species colonies of A. cerana and its sibling species Apis mellifera under queenright and queenless conditions. In both queenless and queenright conspecific colonies, the proportion of A. cerana workers with activated ovaries was significantly greater than the proportion of A. mellifera workers with activated ovaries. Apis cerana workers showed significantly greater ovary activation in queenright mixed-species colonies than in conspecific queenright colonies. Moreover, there was significantly greater ovary activation in A. cerana workers in mixed-species colonies headed by A. mellifera queens than A. mellifera workers in mixed-species colonies headed by A. cerana queens. Apis mellifera workers in conspecific queenless colonies showed significantly greater ovary activation than those in mixed-species queenless colonies. Quantification of the chemical components of mandibular gland pheromones of queens of the 2 species showed that they are similar. Combined, our results show that queen signals have been preserved between the 2 species and that workers respond to the heterospecific signals from queens. However, despite the similarity in the queen mandibular gland fatty acid secretions between the 2 species, workers respond differentially toward hetero- and conspecific queens. [ABSTRACT FROM PUBLISHER]

Pheromones cause dramatic changes in behavior and physiology, and are critical for honey bee colony organization. Queen mandibular pheromone (QMP) regulates multiple behaviors in worker bees (Slessor et al. in J Chem Ecol 31(11):2731–2745, ). We also identified genes whose brain expression levels were altered by exposure to QMP (Grozinger et al. in Proc Natl Acad Sci USA 100(Suppl 2):14519–14525, ). Krüppel-homolog 1 ( Kr-h1) RNA levels were significantly downregulated by QMP, and were higher in foragers than in nurses (Whitfield et al. in Science 302(5643):296–299, ). Here we report on results of behavioral and pharmacological experiments that characterize factors regulating expression of Kr-h1. Foragers have higher brain levels of Kr-h1 than in-hive bees, regardless of age and pheromone exposure. Furthermore, forager Kr-h1 levels were not affected by QMP. Since the onset of foraging is caused, in part, by increasing juvenile hormone blood titers and brain octopamine levels, we investigated the effects of octopamine and methoprene (a juvenile hormone analog) on Kr-h1 expression. Methoprene produced a marginal (not significant) increase in Kr-h1 expression, but Kr-h1 brain levels in methoprene-treated bees were no longer downregulated by QMP. Octopamine did not modulate Kr-h1 expression. Our results demonstrate that the gene expression response to QMP is not hard-wired in the brain but is instead dependent on worker behavioral state. [ABSTRACT FROM AUTHOR]

The influence of the queen and her pheromonal signal on comb construction was examined. We tested four treatments with newly hived packages of bees containing: 1) a mated queen, 2) a virgin queen, 3) no queen but with a dispenser containing synthetic queen mandibular pheromone (QMP), and 4) no queen and no pheromone. After 10 days, the comb produced by each colony was removed, comb measurements made, bees from the comb-building area collected, the size of the scales on the wax mirrors of the collected bees ranked on a scale of 0-4 and the queens removed and analyzed for QMP components. Queenless workers built substantially less comb and the comb they did build had significantly larger, drone-sized cells than for the other 3 treatments, indicating that both cell size and the quantity of comb built are mediated through the queen, particularly QMP. The observations of wax scale size suggested that QMP influenced comb building behaviour rather than wax scale production. These results support the idea that queenless honey bees can adopt a strategy of constructing drone-sized cells in order to increase reproductive fitness through male production following queen loss. [ABSTRACT FROM AUTHOR]