Sensori-motor learning and its relevance for task specialization in bumble bees

Individual bees often restrict their visits to only a few species out of the multitude of available plants. This flower constancy is likely caused by limitations of memory for motor patterns, sensory stimuli, or reward levels. Here we test the implications of sensori-motor learning and memory for flower constancy. Artificial “flowers” with two distinct “morphologies” were used, so that in each flower type, a different motor pattern was needed to reach the nectar. As in natural flowers, these morphological types were associated with sensory signals (blue and yellow color stimuli). Bees which learned only a single task were more efficient in several ways than those which had learned two: they made fewer errors, had shorter flower handling times, took shorter times to correct errors, and transitions between flowers were initially more rapid. For bees which had learned two tasks, performance depended strongly on the training schedule: if each task was learned with blocked trials, the memory for the second appeared to interfere with that for the first. Interference affected only the association between flower signal and motor pattern, not the motor pattern itself. This was not the case if bees were trained for both tasks with alternating trials. In that case, bees rapidly learned both tasks, albeit with worse saturation levels than bees which had learned only one. Bees transferred the experience gained on one task to a second task: their initial performance on the second task was better than their initial performance on the first. On the other hand, performance on the second task in the saturation level (in which bees no longer improve their efficiency) was worse than on the first task (negative transfer). In the saturation phase, performance did not directly depend on switch frequency, but on whether the bee had one or two options in memory. Thus, while bees would become proficient at two tasks more quickly if their acquisition phase included switches, such switches had no measurable effect in the saturation phase. The implications of these findings for foraging are discussed using modern learning theory. Received: 4 April 1997 / Accepted after revision: 8 August 1997     

How floral odours are learned inside the bumblebee (Bombus terrestris) nest

Recruitment in social insects often involves not only inducing nestmates to leave the nest, but also communicating crucial information about finding profitable food sources. Although bumblebees transmit chemosensory information (floral scent), the transmission mechanism is unknown as mouth-to-mouth fluid transfer (as in honeybees) does not occur. Because recruiting bumblebees release a pheromone in the nest that triggers foraging in previously inactive workers, we tested whether this pheromone helps workers learn currently rewarding floral odours, as found in food social learning in rats. We exposed colonies to artificial recruitment pheromone, paired with anise scent. The pheromone did not facilitate learning of floral scent. However, we found that releasing floral scent in the air of the colony was sufficient to trigger learning and that learning performance was improved when the chemosensory cue was provided in the nectar in honeypots; probably because it guarantees a tighter link between scent and reward, and possibly because gustatory cues are involved in addition to olfaction. Scent learning was maximal when anise-scented nectar was brought into the nest by demonstrator foragers, suggesting that previously unidentified cues provided by successful foragers play an important role in nestmates learning new floral odours.     

Bees use three-dimensional information to improve target detection

Bumblebee detection of a flat circular disc (two-dimensional (2D) presentation) and a disc which was presented 10 cm in front of a structured background (and thus provided three-dimensional (3D) cues) was compared. A dual choice test using a Y-maze apparatus was conducted to estimate the minimum visual angle at which the bees were able to detect the disc. At large visual angles of 15, 10 and 5° bees’ performance between the 2D and the 3D presentation did not differ. However, when the disc subtended 3° at the bee’s eye, the bees performed significantly better when 3D information was available. Overall, bees were able to detect a target subtending a 40% smaller visual angle when it was presented in front of the structured background compared to a 2D presentation. This suggests that previous reports on the limits of target detection in bees using flat stimuli might have underestimated the bees’ ability to locate small flowers under natural conditions. Bees use motion parallax, i.e. the apparent relative motion of a stationary object against a background, for perceiving the third dimension. Our data suggest that bumblebees can integrate information from at least two types of feature detectors, motion and area, to improve single target detection.     

Pollen foraging: learning a complex motor skill by bumblebees (<Emphasis Type="Italic">Bombus terrestris</Emphasis>)

To investigate how bumblebees (Bombus terrestris) learn the complex motor skills involved in pollen foraging, we observed naïve workers foraging on arrays of nectarless poppy flowers (Papaver rhoeas) in a greenhouse. Foraging skills were quantified by measuring the pollen load collected during each foraging bout and relating this to the number of flowers visited and bout duration on two consecutive days. The pollen standing crop (PSC) in each flower decreased drastically from 0530 to 0900 hours. Therefore, we related foraging performance to the changing levels of pollen available (per flower) and found that collection rate increased over the course of four consecutive foraging bouts (comprising between 277 and 354 individual flower visits), suggesting that learning to forage for pollen represents a substantial time investment for individual foragers. The pollen collection rate and size of pollen loads collected at the start of day 2 were markedly lower than at the end of day 1, suggesting that components of pollen foraging behaviour could be subject to imperfect overnight retention. Our results suggest that learning the necessary motor skills to collect pollen effectively from morphologically simple flowers takes three times as many visits as learning how to handle the most morphologically complex flowers to extract nectar, potentially explaining why bees are more specialised in their choice of pollen flowers.     

Size-resolved simulation of particulate matters and CO2 concentration in passenger vehicle cabins

Environmental Science and Pollution Research - The main aim of this study is to develop a mathematical size-dependent vehicle cabin model for particulate matter concentration including PM2.5...     

Methods for measuring denitrification: diverse approaches to a difficult problem.

Denitrification, the reduction of the nitrogen (N) oxides, nitrate (NO3-) and nitrite (NO2-), to the gases nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2), is important to primary production, water quality, and the chemistry and physics of the atmosphere at ecosystem, landscape, regional, and global scales. Unfortunately, this process is very difficult to measure, and existing methods are problematic for different reasons in different places at different times. In this paper, we review the major approaches that have been taken to measure denitrification in terrestrial and aquatic environments and discuss the strengths, weaknesses, and future prospects for the different methods. Methodological approaches covered include (1) acetylene-based methods, (2) 15N tracers, (3) direct N2 quantification, (4) N2:Ar ratio quantification, (5) mass balance approaches, (6) stoichiometric approaches, (7) methods based on stable isotopes, (8) in situ gradients with atmospheric environmental tracers, and (9) molecular approaches. Our review makes it clear that the prospects for improved quantification of denitrification vary greatly in different environments and at different scales. While current methodology allows for the production of accurate estimates of denitrification at scales relevant to water and air quality and ecosystem fertility questions in some systems (e.g., aquatic sediments, well-defined aquifers), methodology for other systems, especially upland terrestrial areas, still needs development. Comparison of mass balance and stoichiometric approaches that constrain estimates of denitrification at large scales with point measurements (made using multiple methods), in multiple systems, is likely to propel more improvement in denitrification methods over the next few years.     

Sources, fate, and toxic hazards of oxygenated polycyclic aromatic hydrocarbons (PAHs) at PAH-contaminated sites

In this paper we show that oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) are important cocontaminants that should be taken into account during risk assessment and remediation of sites with high levels of PAHs. The presented data, which have been collected both from our own research and the published literature, demonstrate that oxy-PAHs are abundant but neglected contaminants at these sites. The oxy-PAHs show relatively high persistency and because they are formed through transformation of PAHs, their concentrations in the environment may even increase as the sites are remediated by methods that promote PAH degradation. Furthermore, we show that oxy-PAHs are toxic to both humans and the environment, although the toxicity seems to be manifested through other effects than those known to be important for polycyclic aromatic compounds in general, that is, mutagenicity and carcinogenicity. Finally, we present data that support the hypothesis that oxy-PAHs are more mobile in the environment than PAHs, due to their polarity, and thus have a higher tendency to spread from contaminated sites via surface water and groundwater. We believe that oxy-PAHs should be included in monitoring programs at PAH-contaminated sites, even if a number of other toxicologically relevant compounds that may also be present, such as nitro-PAHs and azaarenes, are not monitored. This is because oxy-PAH levels are difficult to predict from the PAH levels, because their environmental behavior differs substantially from that of PAHs, and oxy-PAHs may be formed as PAHs are degraded.     

The Responsibility of Farmers,Public Authorities and Consumers for Safeguarding Bees Against Harmful Pesticides

Journal of Agricultural and Environmental Ethics - This study examines the influence of environmental values on consumer intentions to participate in agritourism through the theory of planned...