Learning at Old Age: A Study on Winter Bees

Ageing is often accompanied by a decline in learning and memory abilities across the animal kingdom. Understanding age-related changes in cognitive abilities is therefore a major goal of current research. The honey bee is emerging as a novel model organism for age-related changes in brain function, because learning and memory can easily be studied in bees under controlled laboratory conditions. In addition, genetically similar workers naturally display life expectancies from 6 weeks (summer bees) to 6 months (winter bees). We studied whether in honey bees, extreme longevity leads to a decline in cognitive functions. Six-month-old winter bees were conditioned either to odours or to tactile stimuli. Afterwards, long-term memory and discrimination abilities were analysed. Winter bees were kept under different conditions (flight/no flight opportunity) to test for effects of foraging activity on learning performance. Despite their extreme age, winter bees did not display an age-related decline in learning or discrimination abilities, but had a slightly impaired olfactory long-term memory. The opportunity to forage indoors led to a slight decrease in learning performance. This suggests that in honey bees, unlike in most other animals, age per se does not impair associative learning. Future research will show which mechanisms protect winter bees from age-related deficits in learning

Survival rate and changes in foraging performances of solitary bees exposed to a novel insecticide

Abstract Solitary bees are among the most important pollinators worldwide however population declines especially in croplands has been noticed. The novel pesticide sulfoxaflor is a competitive modulator of nicotinic acetylcholine receptors (nAChR) in insects. While there is evidence of a negative impact of neonicotinoids on bees of several social organization levels, our overall knowledge on the impact of sulfoxaflor on bees is poor. Here we present for the first time a study showing effects of field realistic doses of sulfoxaflor on solitary bees. Bees submitted to long term exposure of field realistic doses of sulfoxaflor (5 µg dm-3, 10 µg dm-3, 50 µg dm-3) and control were observed regarding their survival rate. Moreover, we recorded metrics related to flower visitation and flight performance. We discover that the highest field realistic dose is lethal to Osmia bicornis along five days of exposure. The effect of sulfoxaflor reduces the outcome of foraging, important features for fruit and seed production of cross-pollinated plant species. Bees exposed to pesticide visited flowers mostly walking rather than flying. Flight performance was also impaired by the pesticide

A Novel Thermal-Visual Place Learning Paradigm for Honeybees (Apis mellifera)

Honeybees (Apis mellifera) have fascinating navigational skills and learning capabilities in the field. To decipher the mechanisms underlying place learning in honeybees, we need paradigms to study place learning of individual honeybees under controlled laboratory conditions. Here, we present a novel visual place learning arena for honeybees which relies on high temperatures as aversive stimuli. Honeybees learn to locate a safe spot in an unpleasantly warm arena, relying on a visual panorama. Bees can solve this task at a temperature of 46C, while at temperatures above 48C bees die quickly. This new paradigm, which is based on pioneering work on Drosophila, allows us now to investigate thermal-visual place learning of individual honeybees in the laboratory, for example after controlled genetic knockout or pharmacological intervention

The Bacterium Pantoea ananatis Modifies Behavioral Responses to Sugar Solutions in Honeybees

1. Honeybees, which are among the most important pollinators globally, do not only collect pollen and nectar during foraging but may also disperse diverse microbes. Some of these can be deleterious to agricultural crops and forest trees, such as the bacterium Pantoea ananatis, an emerging pathogen in some systems. P. ananatis infections can lead to leaf blotches, die-back, bulb rot, and fruit rot. 2. We isolated P. ananatis bacteria from flowers with the aim of determining whether honeybees can sense these bacteria and if the bacteria affect behavioral responses of the bees to sugar solutions. 3. Honeybees decreased their responsiveness to different sugar solutions when these contained high concentrations of P. ananatis but were not deterred by solutions from which bacteria had been removed. This suggests that their reduced responsiveness was due to the taste of bacteria and not to the depletion of sugar in the solution or bacteria metabolites. Intriguingly, the bees appeared not to taste ecologically relevant low concentrations of bacteria. 4. Synthesis and applications. Our data suggest that honeybees may introduce P.ananatis bacteria into nectar in field-realistic densities during foraging trips and may thus affect nectar quality and plant fitness

Zuckerwasserreaktion und Verhalten in Honigbienen (Apis mellifera L.)

In dieser Arbeit wird bei der Honigbiene (Apis mellifera L.) analysiert, wie sich die individuelle Empfindlichkeit für Zuckerwasserreize auf verschiedene Formen der Verhaltensplastizität auswirkt. Die Versuche klären insbesondere die Rolle des Belohnungsreizes Zuckerwasser beim assoziativen und nicht-assoziativen Lernen auf. In den Untersuchungen werden Bienen verschiedenen Genotyps, verschiedenen Alters und mit verschiedener Sammelrolle verwendet. Die Funktion von potentiellen endogenen Modulatoren und von intrazellulären Signalmolekülen auf die Zuckerwasserempfindlichkeit wird analysiert. Die individuelle Empfindlichkeit für Zuckerwasserreize wird mit Hilfe des Rüsselreflexes oder durch Ableitungen am Proboscismuskels M17 bestimmt. Die Versuche zeigen, daß Pollensammlerinnen empfindlicher für Zuckerwassereize als Nicht-Pollensammlerinnen sind, Bienen der genetischen Linie "high pollen hoarding" sind empfindlicher als solche der Linie "low-pollen hoarding". Ältere Sammlerbienen sind empfindlicher als Jungbienen. Die individuelle Zuckerwasserempfindlichkeit bestimmt beim taktilen und olfaktorischen assoziativen Lernen in starkem Maße den Verlauf von Akquisition, Extinktion und Diskriminierung. Dabei ist die Zuckerwasserperzeption an der Proboscis für das Lernniveau entscheidender als die an der Antenne. Auch beim nicht-assoziativen Lernen determiniert die individuelle Zuckerwasserempfindlichkeit den Grad und den Verlauf von Habituation und Sensitisierung. Liganden für biogene Amin-Rezeptoren können die Zuckerwasserreaktion modulieren. Die Injektion von Oktopamin und Tyramin erhöht die Zuckerwasserempfindlichkeit, während Dopamin und der Dopamin-Rezeptor-Agonist 6,7-ADTN funktionell antagonistisch wirken. Die Aktivität der PKA im Antennallobus korreliert mit der Zuckerwasserempfindlichkeit. Bienen mit niedriger Empfindlichkeit zeigen eine signifikant niedrigere PKA-Aktivität als Bienen mit hoher Zuckerwasserempfindlichkeit. Die hier vorgestellten Experimente zeigen, daß die Zuckerwasserempfindlichkeit einer Biene alle untersuchten Formen des Lernens entscheidend beeinflußt. Damit ist ein wichtiger Faktor identifiziert worden, der durch biogene Amine moduliert werden kann und der Unterschiede der Verhaltensplastizität bei Bienen erklärt.This work shows the effects of individual sucrose responsiveness on two forms of associative and non-associative learning in the honey bee. In addition, the effects of genotype, foraging role and age on sucrose responsiveness, associative learning and discrimination are presented. It is tested whether myograms of the proboscis muscle 17 can determine sucrose responsiveness more accurately than behavioural tests. It is further analysed whether the three biogenic amines octopamine, tyramine and dopamine, and the dopamine receptor agonist ADTN can modulate sucrose responsiveness. In search of neuronal correlates for sucrose responsiveness the activity of cAMP-dependent protein kinase (PKA) in the antennal lobes of bees with different sucrose responsiveness is studied. Sucrose responsiveness varies between individuals of different genotypes, foraging roles or ages. Associative tactile and olfactory learning is strongly affected by individual sucrose responsiveness. Bees with high sucrose responsiveness show a higher acquisition level and less extinction than individuals with low sucrose responsiveness. Genotype or foraging role have no separate effects on associative learning or extinction. Age has an additional effect on acquisition, which cannot be explained by differences in sucrose responsiveness. Discrimination depends on acquisition and is thus indirectly related to sucrose responsiveness. Genotype has a separate effect on discrimination in foragers but not in preforagers. The short sucrose stimulation of the antenna during associative tactile learning only has a week effect on the learning performance. The sucrose concentration offered to the proboscis as reward strongly determines the level of acquisition and extinction. Discrimination is best when antenna and proboscis are stimulated with a low sucrose concentration. The degree of non-associative habituation and sensitisation is strongly determined by individual sucrose responsiveness. Bees with high sucrose responsiveness demonstrate weaker habituation and stronger sensitisation than bees with low sucrose responsiveness. The sucrose concentration of the habituating or sensitising stimuli strongly affects habituation and sensitisation. Age affects habituation but not sensitisation. Sucrose responsiveness can be exactly determined by myograms from the proboscis muscle 17, which differs in its spike rate when the antennae of a bee are stimulated with different sucrose concentrations, even when the bee responds with proboscis extension to all sucrose concentrations offered. Modulation of sucrose responsiveness by biogenic amines is possible. Octopamine and tyramine injections result in a dose-dependent increase in sucrose responsiveness. Dopamine and ADTN decrease sucrose responsiveness in a dose-dependent manner. This modulation of sucrose responsiveness is reversible. Sucrose responsiveness covaries with PKA activity in the antennal lobes. Bees with high sucrose responsiveness show higher PKA activity than bees with low sucrose responsiveness. Thirty minutes after feeding, PKA activity is higher than 90 min after feeding. These findings show that individual sucrose responsiveness is a very good indicator of the "physiological state" of a bee and can explain a large part of individual differences in non-associative and associative learning. The neuronal mechanisms regulating individual sucrose responsiveness are not yet known, but PKA activity in the antennal lobes and biogenic amines appear to be involved in these processes

Effects of the novel pesticide flupyradifurone (Sivanto) on honeybee taste and cognition

Due to intensive agriculture honeybees are threatened by various pesticides. The use of one group of them, the neonicotinoids, was recently restricted by the European Union. These chemicals bind to the nicotinic acetylcholine receptor (nAchR) in the honeybee brain. Recently, Bayer AG released a new pesticide by the name of “Sivanto” against sucking insects. It is assumed to be harmless for honeybees, although its active ingredient, flupyradifurone, binds nAchR similar to the neonicotinoids. We investigated if this pesticide affects the taste for sugar and cognitive performance in honeybee foragers. These bees are directly exposed to the pesticide while foraging for pollen or nectar. Our results demonstrate that flupyradifurone can reduce taste and appetitive learning performance in honeybees foraging for pollen and nectar, although only the highest concentration had significant effects. Most likely, honeybee foragers will not be exposed to these high concentrations. Therefore, the appropriate use of this pesticide is considered safe for honeybees, at least with respect to the behaviors studied here

Effects of patriline on gustatory responsiveness and olfactory learning in honey bees

Associative proboscis extension learning differs widely among bees of a colony. This variety of performances is often related to differences in sucrose responsiveness, which determines learning performance. Sucrose responsiveness is partly determined genetically. We studied for the first time effects of paternal genes on associative learning independent of sucrose responsiveness. To do this, we used wild-type workers stemming from five unrelated patrilines. Bees of the patrilines were first tested for sucrose responsiveness. Only bees with equal sucrose responsiveness were analysed for associative olfactory learning, memory and discrimination. The bees of different patrilines did not differ in their acquisition, memory or discrimination of odours when they had similar sucrose responsiveness. But patrilines differed significantly in their sucrose responsiveness. This shows genetic effects on sensory responsiveness but no independent effects on associative learning

The ant’s weapon improves honey bee learning performance

Abstract Formic acid is the main component of the ant’s major weapon against enemies. Being mainly used as a chemical defense, the acid is also exploited for recruitment and trail marking. The repelling effect of the organic acid is used by some mammals and birds which rub themselves in the acid to eliminate ectoparasites. Beekeepers across the world rely on this effect to control the parasitic mite Varroa destructor. Varroa mites are considered the most destructive pest of honey bees worldwide and can lead to the loss of entire colonies. Formic acid is highly effective against Varroa mites but can also kill the honeybee queen and worker brood. Whether formic acid can also affect the behavior of honey bees is unknown. We here study the effect of formic acid on sucrose responsiveness and cognition of honey bees treated at different live stages in field-relevant doses. Both behaviors are essential for survival of the honey bee colony. Rather unexpectedly, formic acid clearly improved the learning performance of the bees in appetitive olfactory conditioning, while not affecting sucrose responsiveness. This exciting side effect of formic acid certainly deserves further detailed investigations