Satiation differentially affects performance in a learning assay by nurse and forager honey bees

When not satiated prior to training, there were no differences between foragers and nurse honey bees in the acquisition of an appetitively based conditioned response in an olfactory associative learning assay, but when satiated foragers showed faster acquisition than did nurses. Satiation-related differences between foragers and nurses were more a function of behavioral state than age, because satiated precocious foragers also showed faster acquisition rates than did satiated nurse bees, despite their similar ages. Tests of sucrose responsiveness and retention of conditioned responses indicate that the observed performance differences between nurses and foragers were more likely due to differential sensitivity of sensory and motor processes related to satiation rather than differences in cognitive ability.     

Visual associative learning in restrained honey bees with intact antennae

A restrained honey bee can be trained to extend its proboscis in response to the pairing of an odor with a sucrose reward, a form of olfactory associative learning referred to as the proboscis extension response (PER). Although the ability of flying honey bees to respond to visual cues is well-established, associative visual learning in restrained honey bees has been challenging to demonstrate. Those few groups that have documented vision-based PER have reported that removing the antennae prior to training is a prerequisite for learning. Here we report, for a simple visual learning task, the first successful performance by restrained honey bees with intact antennae. Honey bee foragers were trained on a differential visual association task by pairing the presentation of a blue light with a sucrose reward and leaving the presentation of a green light unrewarded. A negative correlation was found between age of foragers and their performance in the visual PER task. Using the adaptations to the traditional PER task outlined here, future studies can exploit pharmacological and physiological techniques to explore the neural circuit basis of visual learning in the honey bee.     

Acquisition of a time-memory in forager honey bees

Forager honey bees can associate the time of day with the presence of food at locations outside the hive. It is thought that this time-memory enables the bee to make a spatio-temporal match between its behavior and floral nectar secretion rhythms. Despite a long tradition of research, the mechanisms by which the time-memory becomes established are unknown. We investigated the influences of two experiential factors on the acquisition of time-memory: (1) the number of collecting visits made by the forager within a feeding bout during a restricted time of day and (2) the number of days of exposure to the restricted feeding time. Our results indicate that these two factors control different processes. The number of days of experience influences the temporal accuracy of reconnaissance behavior to the food source. The cumulative number of collecting visits within the feeding bouts has no apparent effect on time-accuracy but, instead, determines the probability of exhibiting food-anticipatory behavior and, if that overt behavior is performed, the intensity of its expression. This paper is dedicated to the memory of Prof. James L. Larimer.     

Juvenile hormone and aggression in honey bees

We determined whether defense by individual bees against non-nestmates in honey bees (Apis mellifera) is correlated with their juvenile hormone (JH) titers, which are known to vary developmentally and seasonally. We bioassayed winter and summer bees for aggressive and non-aggressive individuals. Bees in winter could not be distinguished by task group, but bees in summer were segregated into nurses and guards. JH titers were correlated with aggressive behavior at two levels. First, winter bees and summer nurses, known to have lower JH titers, both showed less aggression toward foreign bees than did summer guards. Second, aggressive individuals had significantly higher JH titers than did non-aggressive bees within each colony. Inter-colonial variation in aggressiveness was maintained during summer and winter, suggesting a genetic basis for these differences. An alarm pheromone test further substantiated the existence of inter-colonial differences. We found significant variation in JH titers among different colonies, but this variation was not significantly associated with colony-level aggressiveness. The correlation between JH and levels of aggressiveness within a colony suggests a regulatory role for JH, but variation among colonies involves factors other than JH.     

Vitellogenesis in Varroa jacobsoni,a parasite of honey bees

Reproduction in Varroa jacobsoni occurs only in cells of the capped honey bee brood. Female mites were sampled at different times after cell sealing and ovaries containing a vitellogenic oocyte of the first gonocycle were examined under an electron microscope. It was found that the cytoplasmic connection between the lyrate organ and the oocyte persists far into the vitellogenic growth phase. In addition, a large amount of yolk material is taken up from the haemolymph. All ultrastructural features characteristic of vitellogenesis, such as microvilli, coated pits, vesicles and growing yolk platelets, are present. If more than four Varroa females live in an overcrowded brood cell, they appear to be in stress conditions and their vitellogenic oocytes may become atretic. Alterations typical for oocyte degradation and oosorption were observed in such situations.     

Differential sensitivity of honey bees and bumble bees to a dietary insecticide (imidacloprid)

Currently, there is concern about declining bee populations and the sustainability of pollination services. One potential threat to bees is the unintended impact of systemic insecticides, which are ingested by bees in the nectar and pollen from flowers of treated crops. To establish whether imidacloprid, a systemic neonicotinoid and insect neurotoxin, harms individual bees when ingested at environmentally realistic levels, we exposed adult worker bumble bees, Bombus terrestris L. (Hymenoptera: Apidae), and honey bees, Apis mellifera L. (Hymenoptera: Apidae), to dietary imidacloprid in feeder syrup at dosages between 0.08 and 125 μg l^?1. Honey bees showed no response to dietary imidacloprid on any variable that we measured (feeding, locomotion and longevity). In contrast, bumble bees progressively developed over time a dose-dependent reduction in feeding rate with declines of 10–30% in the environmentally relevant range of up to 10 μg l^?1, but neither their locomotory activity nor longevity varied with diet. To explain their differential sensitivity, we speculate that honey bees are better pre-adapted than bumble bees to feed on nectars containing synthetic alkaloids, such as imidacloprid, by virtue of their ancestral adaptation to tropical nectars in which natural alkaloids are prevalent. We emphasise that our study does not suggest that honey bee colonies are invulnerable to dietary imidacloprid under field conditions, but our findings do raise new concern about the impact of agricultural neonicotinoids on wild bumble bee populations.     

Cognitive components of color vision in honey bees: how conditioning variables modulate color learning and discrimination

Since the demonstration of color vision in honey bees 100 years ago by Karl von Frisch, appetitive conditioning to color targets has been used as the principal way to access behavioral aspects of bee color vision. Yet, analyses on how conditioning parameters affect color perception remained scarce. Conclusions on bee color vision have often been made without referring them to the experimental context in which they were obtained, and thus presented as absolute facts instead of realizing that subtle variations in conditioning procedures might yield different results. Here, we review evidence showing that color learning and discrimination in bees are not governed by immutable properties of their visual system, but depend on how the insects are trained and thus learn a task. The use of absolute or differential conditioning protocols, the presence of aversive reinforcement in differential conditioning and the degrees of freedom of motor components determine dramatic variations in color discrimination. We, thus, suggest top-down attentional modulation of color vision to explain the changes in color learning and discrimination reviewed here. We discuss the possible neural mechanisms of this modulation and conclude that color vision experiments require a careful consideration of how training parameters shape behavioral responses.     

Tactile learning and the individual evaluation of the reward in honey bees (Apis mellifera L.)

Using the proboscis extension response we conditioned pollen and nectar foragers of the honey bee (Apis mellifera L.) to tactile patterns under laboratory conditions. Pollen foragers demonstrated better acquisition, extinction, and reversal learning than nectar foragers. We tested whether the known differences in response thresholds to sucrose between pollen and nectar foragers could explain the observed differences in learning and found that nectar foragers with low response thresholds performed better during acquisition and extinction than ones with higher thresholds. Conditioning pollen and nectar foragers with similar response thresholds did not yield differences in their learning performance. These results suggest that differences in the learning performance of pollen and nectar foragers are a consequence of differences in their perception of sucrose. Furthermore, we analysed the effect which the perception of sucrose reward has on associative learning. Nectar foragers with uniform low response thresholds were conditioned using varying concentrations of sucrose. We found significant positive correlations between the concentrations of the sucrose rewards and the performance during acquisition and extinction. The results are summarised in a model which describes the relationships between learning performance, response threshold to sucrose, concentration of sucrose and the number of rewards. Accepted: 14 April 1999     

Mortality rates of honey bees in the wild

Senescence, defined as an age-specific decrease in physiological performance accompanied by an increase in mortality rate, has been studied in a wide range of animals including social insects. It is not clear, however, whether honey bees in the wild live long enough to exhibit senescent decline. I tested for the effects of senescence on honey bees foraging in natural settings and documented the predicted pattern of exponential increase in mortality rate with forager age. These data indicate that, in spite of high rates of external mortality, senescence is an important factor determining the performance of insects such as honey bees in the wild. Received 16 November 2007; revised 1 February 2008 and 10 March 2008; accepted 18 March 2008.     

First molecular detection of a viral pathogen in Ugandan honey bees

Ugandan honey bees (Apis mellifera L.) produce honey, and are key pollinators within commercial crops and natural ecosystems. Real-time RT-PCR was used to screen immature and adult bees collected from 63 beekeeping sites across Uganda for seven viral pathogens. No samples tested positive for Chronic bee paralysis virus, Sacbrood virus, Deformed wing virus, Acute bee paralysis virus, Apis iridescent virus or Israeli acute paralysis virus. However, Black queen cell virus (BQCV) was found in 35.6% of samples. It occurred in adults and larvae, and was most prevalent in the Western highlands, accounting for over 40% of positive results nationally.     

The dynamics of sleep-like behaviour in honey bees

At night, honey bees pass through a physiological state that is similar to mammalian sleep. Like sleep in mammals, sleep-like behaviour in honey bees is an active process. This is expressed most clearly in these insects by spontaneous antennal movements which appear at irregular intervals throughout the night and interrupt episodes of antennal immobility. Here we present a newly developed video technique for the continuous recording of the position and movements of the bee's antennae. The same technique was used to record head inclination and ventilatory movements. Despite the constancy of the ambient temperature, the magnitudes of antennae-related parameters, as well as head inclination and ventilatory cycle duration, displayed dynamic unimodal time-courses which exhibited a high degree of temporal covariance. The similarity between these time-courses and the nightly time-course of the reaction threshold for a sensory stimulus, investigated previously, indicates that, in honey bees, deepest "sleep" and least ventilatory activity occur at the same time (in the 7th hour of the rest phase).Abbreviations DD continuous darkness - EMG electromyogram - LD periodic alternation between light (L) and darkness (D) - MEST Middle European Summer Time (UTC+2 h); - UV ultraviolet This paper is dedicated to Professor Martin Lindauer, who—to our knowledge—was the first to meticulously record the nightly behaviour of honey bees (Lindauer 1952) and who also inspired one of us (W.K.) to investigate antennal motility during nightly rest in these animals.     

Isolation of chitin and chitosan from honey bees

The procedure of isolation of chitin, chitosan, and water-soluble low-molecular-weight chitin from the corpses of bees was developed. This procedure included deproteinization of the corpses of bees, discoloration of the chitin-melanin complex, deacetylation, and enzymatic hydrolysis of chitosan.     

Dopamine and octopamine regulate 20-hydroxyecdysone level in vivo in Drosophila

The effects of increased level of dopamine (DA) (feeding flies with DA precursor, L-dihydroxyphenylalanine, L-DOPA) on the level of 20-hydroxyecdysone (20E) and on juvenile hormone (JH) metabolism in young (2-day-old) wild type females (the strain wt) of Drosophila virilis have been studied. Feeding the flies with L-DOPA increased DA content by a factor of 2.5, and led to a considerable increase in 20E level and a decrease of JH degradation (an increase in JH level). We have also measured the levels of 20E in the young (1-day-old) octopamineless females of the strain Tbetah(nM18) and in wild type females, Canton S, of D. melanogaster. The absence of OA led to a considerable decrease in 20E level (earlier it was shown that in the Tbetah(nM18) females, JH degradation was sharply increased). We have studied the effects of JH application on 20E level in 2-day-old wt females of D. virilis and demonstrated that an increase in JH titre results in a steep increase of 20E level. The supposition that biogenic amines act as intermediary between JH and 20E in the control of Drosophila reproduction is discussed.