Hygienic behaviour in the Australian stingless bees Tetragonula carbonaria and T. hockingsi

Hygienic behaviour is a natural mechanism of colony-level disease resistance to brood pathogens and has been reported in honey bees and stingless bees. A novel brood disease was recently confirmed in the Australian stingless bees Tetragonula carbonaria Smith and Tetragonula hockingsi Cockerell and there is a paucity of data available on hygienic behaviour in these species. To address this, we investigated hygienic behaviour in eight colonies of T. carbonaria and four colonies of T. hockingsi, using brood freeze-kill and pin-kill assays. Hygienic behaviour was present in both species and was rapidly expressed in both assays. In T. carbonaria, the mean time (± SE) for removal of freeze-killed and pin-killed brood was 9.1 ± 1.9 hours and 8.2 ± 0.9 hours, respectively (n=8; one trial per assay). In T. hockingsi, removal of freeze-killed and pin-killed brood was 14.1 ± 5.1 hours and 10.4 (no SE) hours, respectively. There was no significant difference (α=0.05) in time taken to complete the hygienic behaviour phases (detection, uncapping, removal or cell dismantling) between assay type or assay order in both species. However, intercolony variation was observed in both species in the assays, suggesting that like honey bees, hygienic behaviour may have a genetic component. Tetragonula carbonaria and T. hockingsi displayed significantly faster detection, uncapping, removal and cell dismantling times than any of the stingless bees or most honey bees studied previously. This may, in part, explain why stingless bees appear to suffer from relatively few brood diseases

Moving without a purpose : an experimental study of swarm guidance in the Western honey bee, Apis mellifera

During reproductive swarming, honey bee scouts perform two very important functions. Firstly, they find new nesting locations and return to the swarm cluster to communicate their discoveries. Secondly, once the swarm is ready to depart, informed scout bees act as guides, leading the swarm to its final destination. We have previously hypothesised that the two processes, selecting a new nest site and swarm guidance, are tightly linked in honey bees. When swarms can be laissez faire about where they nest, reaching directional consensus prior to lift off seems unnecessary. If, in contrast, it is essential that the swarm reaches a precise location, either directional consensus must be near unanimous prior to swarm departure or only a select subgroup of the scouts guide the swarm. Here, we tested experimentally whether directional consensus is necessary for the successful guidance of swarms of the Western honey bee Apis mellifera by forcing swarms into the air prior to the completion of the decision-making process. Our results show that swarms were unable to guide themselves prior to the swarm reaching the pre-flight buzzing phase of the decision-making process, even when directional consensus was high. We therefore suggest that not all scouts involved in the decision-making process attempt to guide the swarm

Bee-friendly community gardens : impact of environmental variables on the richness and abundance of exotic and native bees

With their abundant floral resources, urban community gardens have the potential to play an important role in pollinator conservation. At the same time, the gardens themselves are dependent upon the pollination services provided by insects. Thus, understanding the variables that can increase bee richness or abundance in community gardens can contribute to both urban agriculture and pollinator conservation. Here we examine the impact of several environmental variables on bee abundance and diversity in urban community gardens in Sydney, Australia. We used hand netting and trap nests to sample bees in 27 community gardens ranging from inner city gardens with limited surrounding green space, to suburban gardens located next to national parks. We did not find strong support for an impact of any of our variables on bee species richness, abundance or diversity.We found high abundance of a recently introduced non-native bee: the African carder bee, Afranthidium repetitum (Schulz 1906). The abundance of African carder bees was negatively correlated with the amount of surrounding green space and positively correlated with native bee abundance/ species richness. Our results highlight the seemingly rapid increase in African carder bee populations in inner city Sydney, and we call for more research into this bee’s potential environmental impacts. Our results also suggest that hard-to-change environmental factors such as garden size and distance to remnant forests may not have a strong influence on native bee diversity and abundance in highly urbanized area

Honeybee, Apis mellifera, guards use adaptive acceptance thresholds to limit worker reproductive parasitism

To protect their colonies from robbing by conspecifics, honeybees have evolved nest-guarding behaviour. Guards adjust their acceptance threshold so that, as the likelihood of robbing increases, fewer non-nestmates are admitted. In addition to the possibility of robbing, queenless colonies may be infiltrated by reproductively parasitic non-nestmates.We tested the hypothesis that queenless colonies would be more discriminatory of non-nestmates than queenright colonies. As predicted, queenless colonies accepted significantly fewer non-nestmates (from queenright colonies) than they did nestmates, whereas queenright colonies did not differentiate significantly between the two sources. This trend continued once laying workers became active in queenless colonies. Thus there is evidence that queenless colonies are more discerning against potential reproductive parasites than queenright colonies. We also tested the hypothesis that as the likelihood of an intruder being a reproductive parasite increased, guards would become less permissive of allowing it entrance to the colony. Queenright colonies accepted significantly more non-nestmates from queenright colonies (no active ovaries) than they did non-nestmates from queenless colonies (many with active ovaries). However, queenless colonies did not make this distinction. We suggest that to queenless colonies all non-nestmates are potential parasites

Inaccurate and unverified information in decision making : a model for the nest site selection process of Apis florea

We present an agent-based model for the nest site selection process of the open-nesting red dwarf honeybee, Apis florea. Our main aim was to determine how nest site requirements affect the bees’ decision-making process. We either calculated our model parameters from experimental data or chose them so that our model would generate similar numbers of dancing bees and dance followers to those observed in real swarms with access to an abundance of suitable nest sites in all directions. We found that A. florea is less capable of making a collective decision on a new nest site when the area occupied by suitable sites is small compared to when suitable sites are abundant. Increasing the use of information regarding the location of potential nest sites or the accuracy of the information available enhanced the decision-making ability of A. florea when nest sites were scarce. We also found that swarm guidance might be hindered when suitable nest site areas are wide apart. We therefore examined two possible mechanisms for increasing directional agreement among dancers: mimicry of unverified dance information and self-regulation by inhibiting or changing dance behaviour based on observations of other dances. We show that, even at low levels, dance mimicry greatly enhances the ability of an A. florea swarm to make a decision and reduces the time to make a decision. However, in the presence of mimicry errors propagate through the swarm. Self-regulation had little or no effect, probably because of the overall low levels of dance activity present on the swarm at any given time. Our model results suggest that A. florea’s decision-making process allows swarms to locate a new nest site provided nest sites are abundant, even when they are of similar quality

Do small swarms have an advantage when house hunting? : the effect of swarm size on nest-site selection by Apis mellifera

Reproductive swarms of honeybees are faced with the problem of finding a good site to establish a new colony. We examined the potential effects of swarm size on the quality of nest-site choice through a combination of modelling and field experiments. We used an individual-based model to examine the effects of swarm size on decision accuracy under the assumption that the number of bees actively involved in the decision-making process (scouts) is an increasing function of swarm size. We found that the ability of a swarm to choose the best of two nest sites decreases as swarm size increases when there is some time-lag between discovering the sites, consistent with Janson & Beekman (Janson & Beekman 2007 Proceedings of European Conference on Complex Systems, pp. 204–211.). However, when simulated swarms were faced with a realistic problem of choosing between many nest sites discoverable at all times, larger swarms were more accurate in their decisions than smaller swarms owing to their ability to discover nest sites more rapidly. Our experimental fieldwork showed that large swarms invest a larger number of scouts into the decision-making process than smaller swarms. Preliminary analysis of waggle dances from experimental swarms also suggested that large swarms could indeed discover and advertise nest sites at a faster rate than small swarms

Argentine ants (Linepithema humile) use adaptable transportation networks to track changes in resource quality

Transportation networks play a crucial role in human and animal societies. For a transportation network to be efficient, it must have adequate capacity to meet traffic demand. Network design becomes increasingly difficult in situations where traffic demand can change unexpectedly. In humans, network design is often constrained by path dependency because it is difficult to move a road once it is built. A similar issue theoretically faces pheromone-trail-laying social insects; once a trail has been laid, positive feedback makes rerouting difficult because new trails cannot compete with continually reinforced pre-existing trails. In the present study, we examined the response of Argentine ant colonies and their trail networks to variable environments where resources differ in quality and change unexpectedly. We found that Argentine ant colonies effectively tracked changes in food quality such that colonies allocated the highest proportion of foragers to the most rewarding feeder. Ant colonies maximised access to high concentration feeders by building additional trails and routes connecting the nest to the feeder. Trail networks appeared to form via a pruning process in which lower traffic trails were gradually removed from the network. At the same time, we observed several instances where new trails appear to have been built to accommodate a surge in demand. The combination of trail building when traffic demand is high and trail pruning when traffic demand is low results in a demand-driven network formation system that allows ants to monopolise multiple dynamic resources

Moving home : nest-site selection in the Red Dwarf honeybee (Apis florea)

Abstract The Red Dwarf honeybee (Apis florea) is one of two basal species in the genus Apis. A. florea differs from the well-studied Western Hive bee (Apis mellifera) in that it nests in the open rather than in cavities. This fundamental difference in nesting biology is likely to have implications for nest-site selection, the process by which a reproductive swarm selects a new site to live in. In A. mellifera, workers show a series of characteristic behaviors that allow the swarm to select the best nest site possible. Here, we describe the behavior of individual A. florea workers during the process of nest-site selection and show that it differs from that seen in A. mellifera. We analyzed a total of 1,459 waggle dances performed by 197 scouts in five separate swarms. Our results suggest that two fundamental aspects of the behavior of A. mellifera scouts—the process of dance decay and the process of repeated nest site evaluation—do not occur in A. florea. We also found that the piping signal used by A. mellifera scouts to signal that a quorum has been reached at the chosen site, is performed by both dancing and non-dancing bees in A. florea. Thus, the piping signal appears to serve a different purpose in A. florea. Our results illustrate how differences in nesting biology affect the behavior of individual bees during the nest-site selection process

Collective decision making in the red dwarf honeybee Apis florea : do the bees simply follow the flowers?

Most studies on collective decision making in honeybees have been performed on the cavity-nesting Western honeybee, Apis mellifera. In more recent years, the open-nesting red dwarf honeybee Apis florea has been developed as a model organism of collective decision making in the context of nest-site selection. These studies have shown that the specifics of the species’ nest-site requirements affect collective decision making. In particular, when potential nesting sites are abundant, as is the case in A. florea, the process of collective decision making can be simplified. Here, we ask if A. florea simply follows the availability of floral resources in their environment when deciding on an area to move into. We determined the locations danced for by three colonies the day before, of and after reproductive swarming. Our results suggest that colonies of A. florea indeed track the availability of forage in their environment and that swarms move in the general direction of forage rather than towards a specific nest site

Route selection but not trail clearing are influenced by detour length in the Australian meat ants

Animals travelling through the environment often face trade-offs between environmental parameters such as risk, travel speed and ease of movement when selecting their routes. Route selection is of particular importance for central place foragers like ants, which collectively and repeatedly use trails to exploit stable sources of food. We investigated how colonies of meat ants (Iridomyrmex purpureus) select and clear trail routes when faced with semi-permeable obstructions (strips of grass turf) that substantially slow their travel speed. Meat ant colonies usually re-routed their trails to avoid obstructions when short strips of turf were laid across existing trails, but always travelled directly across the turf when avoiding the turf would have significantly increased travel time. No significant difference in trail clearing activity was found between the short and long obstruction treatments. On binary mazes, meat ants were equally likely to choose paths obstructed with turf and equal length smooth paths, despite much higher time costs associated with the obstructed route. Colonies always chose the shorter, turf-covered path on mazes where the length of the smooth path was increased by 50%, suggesting that meat ants prioritise the minimisation of travel distance when selecting new trail routes. Meat ant route selection and clearing behaviour may reflect a long-term foraging optimisation strategy whereby colonies pay high short-term costs to minimise long-term travelling costs by selecting relatively direct, short distance trail routes which can be cleared of obstructions over time