In advanced eusocial hymenopteran societies workers have ovaries and can lay eggs, but are unable to mate. Workers are more related to their own offspring than to every other member of the colony. So worker reproduction contains both worker-worker and worker-queen conflict. The queen- worker conflict is discussed elsewhere, but if the queen mates with more than two males, worker policing should be selected to lower potential conflicts. However in the Cape honeybee it was predicted that worker policing is absent or less expressed than in other honeybee subspecies, because workers produce female offspring thelytokously. So laying workers and their offspring are nearly genetically identical, which results in the fact that other workers are as related to workers derived from eggs laid by the queen as laid by a worker. However, worker reproduction may be costly and therefore worker policing could be an evolutionary adaptation in the Cape honeybee to lower the costs derived from laying worker activity. Indeed, Cape honeybee colonies show efficient egg removal behaviour, suggesting that other factors like colony efficiency could favour egg removal behaviour. Since egg removal behaviour is a colony phenomenon, factors that affect colony performance could also affect egg removal behaviour. Egg removal behaviour was considerably affected by environmental changes, indicating that other tasks have a higher priority than egg removal behaviour. Thousands of queenright colonies of the neighbouring subspecies (A. m. scutellata) were taken over by laying A. m. capensis workers, showing that A. m. capensis workers are facultative social parasites. These observations strongly indicate that laying workers of A. m. capensis are able to evade worker policing and the inhibitory effects of the queen pheromones, but what potential strategies could these laying workers use to increase the survival of their eggs and evade the queen? On the one hand, egg removal behaviour is variable. One behavioural strategy of laying workers to achieve successful reproduction could be that they lay during periods with low egg removal behaviour. On the other hand, the inhibitory effect of the queen’s pheromones diminishes with distance. Maybe the level of egg removal also depends, like the inhibitory effect of the queen pheromones, on the distance from the queen. Indeed, further away from the queen the effect of the queen pheromone and the level of egg removal is reduced, making successful worker reproduction possible. In both subspecies, A. m. capensis and A. m. scutellata, egg removal behaviour is reduced further away from the queen. In the case of A. m. scutellata egg removal is lacking further away from the queen. This explains why colonies of scutellata are so prone to takeovers by laying Cape honeybee workers. One question in the context of parasitic Cape honeybees is how they manage to get into the host colony. One way could be that they get into the colonies during a natural colony merger which is common in African bees. Two unrelated colonies merged and it took them only 24 hours to show effective integration. Because both colonies are unrelated, the potential reproductive conflict among workers should be more strongly expressed than in a normal colony, which is not the result of a merger. Therefore, the effect of nestmate recognition for eggs on the egg removal behaviour was investigated. The results suggest that workers recognise the origin of an egg and that the standard policing experiments overestimate the level of egg removal and only represent relative values. Moreover, the results show that colony specific components on the eggs are more important than a postulated queen egg marking pheromone. Finally, for the first time empirical evidence from a population of the parasitic laying Cape honeybee workers, invading thousands of colonies of A. m. scutellata in northern South Africa, for a short-sighted selection theory is presented.

In honeybees (Apis mellifera L.) the queen monopolises reproduction. However, especially after queen loss, workers can lay eggs, but are unable to mate. They produce haploid male offspring (drones) from unfertilised eggs via arrhenotokous parthenogenesis. In contrast, workers of the honeybee subspecies Apis mellifera capensis Eschscholtz typically produce diploid female offspring from unfertilised eggs thelytokously. After queen loss and without queen-derived brood A. m. capensis colonies can successfully requeen from worker-derived brood. This, however, is a relatively rare event in wild populations. Moreover, workerderived queens were described to be smaller, more worker-like and reproductively inferior. On the other hand, the fixation of the thelytokous trait relies mainly on sufficient numbers of viable drones produced by worker-derived queens. Small numbers of reproductively inferior worker-derived queens in A. m. capensis populations would be clearly counterintuitive. It is therefore necessary to quantify the significance of worker-dependant queen rearing pathways on the individual (queen) and on population level.Reproductive inferiority of worker-derived queens could not be confirmed on the individual (queen) level when comparing parameters indicating potential reproductive success of queen- and worker-derived queens. Queen- and worker-derived queens clearly showed a congruent range of reproductive performance. In queen rearing preference tests, increased acceptance of worker-derived female larvae was exactly counterbalanced by increased mortality, resulting in an equal number of eclosing virgin queens from an equal number of grafts in both test groups. Larval survival and successful eclosion is a prerequisite for a queen’s reproductive success. I found no difference in eclosion success for queen- and worker-derived virgin queens, indicating a similar potential for reproductive success in both queen types. Assessments of the developmental patterns of colonies headed by both queen and worker-derived queens in long-term experiments revealed no significant differences in reproductive success. Colonies headed by queen-derived queens and colonies headed by worker-derived queens could not be separated when comparing the different developmental pathways observed or from differences in worker-force. Reproductive dominance in A. m. capensis appeared tobe determined by a function of relative compositional and absolute quantitative pheromonal patterns, where individuals, which produce compositionally most queen-like blends in highest quantities, occupy top positions. Queen- and worker-derived virgin queens occupied intermediate positions between pseudoqueens and mated queens. However, no significant differences between the pheromonal status of queen- and worker-derived virgin queens were observed, suggesting a similar range of reproductive dominance for both queen types. In behavioural bioassays queen- and worker-derived virgin queens appeared to be similarly attractive to clustering workers and to drones in a drone congregation area, indicating no differences in potential reproductive success for queens from both origins for those parameters. The significant influence of the queen substance 9-ODA on attractiveness to workers and drones was confirmed. Rare requeening events from worker-derived female brood in queenless A.m. capensis do not satisfactorily explain the fixation of the thelytokous trait at a population level. I observed A. m. capensis worker ovipositing into empty artificial queen cell cups in queen-right colonies. The queen was confined behind a queen excluder grid in a separate compartment of the colony, to imitate reduced pheromonal flow, similar to swarming or superseding colonies. Eggs oviposited by workers in artificial queen cell cups were readily accepted for queen rearing and successful eclosion of viable virgin queens was observed. Consequently I suggested an alternative worker-dependant reproductive pathway in A. m. capensis, which was never described before: In swarming or superseding queenright colonies, laying workers may directly compete with the queen for reproductive success by ovipositing (instead of the queen) into natural queen cell cups. At a population level this reproductive tactic may result in large numbers of worker-derived queens of high reproductive quality in natural populations of A. m. capensis.

The number of drones and genetic diversity among drones are essential components to a well mated queen. Varroa destructor preferentially parasitizes drone brood, and is thought to be responsible for the loss of feral populations that once provided additional drones for honey bee mating areas. It is necessary to use miticides (e.g. coumaphos) in managed colonies to control V. destructor. Little is known about the sublethal effects of these compounds, which are directly introduced into the hive. In response to growing concerns about the successful mating of honey bee queens, drone honey bees were exposed to coumaphos, during drone development. Sperm and seminal vesicles were sampled among drones that were exposed to coumaphos and drones that were not exposed to coumaphos, but were parasitized by Varroa destructor. There were no significant differences found between the two treatments in terms of seminal vesicle size and sperm numbers. These results indicate that drones parasitized by V. destructor have similar sperm quantities as drones exposed to coumaphos. / Graduation date: 2004

Thesis (MSc (Botany and Zoology))--University of Stellenbosch, 2007. / Honeybee queens typically inhibit the reproductive development of workers in the colony. However, African, Apis mellifera scutellata, honeybee queens seem to have little effect on neighbouring A. m. capensis honeybee workers as is evident in the huge losses of African honeybee colonies due to the invasion by ‘social parasitic’ Cape honeybees (pseudoclones). Certain factors; such as queen and brood presence, the level of colony defence and food availability may render host colonies more vulnerable to invasion by the Cape worker honeybees. In this study host African colonies were split to determine whether a “window of opportunity” existed for Cape honeybee infiltration and thus critical to the capensis problem. Nine African colonies were infected with native and pseudoclone Cape workers over different time periods; before, during and after splitting (treatments). I measured survival rates, as well as reproductive and pheromone development of introduced workers. The effect of brood pheromones on Cape worker reproduction was also examined. Approximately 70% of all workers were removed within 72 hours, a critical period to avoid detection by Cape workers. Queen absence significantly affected the success rate of intrusion and establishment by Cape honeybee workers (GLZ; Wald χ² = 4.49, df = 1, P = 0.033). 21% of 21-day old pseudoclones survived African queenless colonies and only 6% queenright colonies. Native Cape workers showed no difference in survival rates between African queenless (12%) and queenright (11%) colonies. Looking at introduction time, considerably more pseudoclone honeybee workers survived in treatment 1 than did native Cape honeybee workers while for treatment 3 the converse was true. These data show no obvious ‘window of opportunity’ surrounding the swarming process promoting Cape honeybee infiltration and establishment of African honeybee colonies, however the period immediately prior to colony fission represents the best opportunity for invasion by pseudoclones. As for ovary and mandibular gland secretion development, all surviving pseudoclones, irrespective of A. m. scutellata queen presence, fully developed their ovaries and concomitantly produced a mandibular gland secretion dominated by 9- oxo-2-decenoic acid (9ODA). Native Cape workers showed low levels of ovary development in queenright host colonies (8-17%) but this was not true for queenless colonies, with all but one worker developing their ovaries when introduced during and after splitting. Only 40% of native Cape workers introduced before splitting developed their ovaries suggesting that queen pheromones in the three days before splitting retarded ovary development in native Cape workers. These data strengthens the suggestion that the pseudoclone honeybee workers have advanced along the queen-worker developmental continuum. Preliminary studies on brood pheromones, an important factor regulating worker reproduction, indicated that Cape workers reproduce quicker and more eggs when exposed to African brood pheromones, compared to both A. m. capensis brood pheromones and no brood pheromones. Pheromones produced by African larvae therefore do not simply inhibit Cape worker reproductive development but accelerate the commencement of egg laying by these workers. On the whole, host African colonies, especially in the absence of their queen, appear vulnerable surrounding colony fission to invasion by both Cape honeybee worker populations even though there are low survival rates. I conclude that these two Cape honeybee worker populations do differ significantly regarding their reproductive capacity and ability in becoming social parasites.

Abstract available in PDF file. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1989.