Honeybee colonies compensate for pesticide-induced effects on royal jelly composition and brood survival with increased brood production.

Sublethal doses of pesticides affect individual honeybees, but colony-level effects are less well understood and it is unclear how the two levels integrate. We studied the effect of the neonicotinoid pesticide clothianidin at field realistic concentrations on small colonies. We found that exposure to clothianidin affected worker jelly production of individual workers and created a strong dose-dependent increase in mortality of individual larvae, but strikingly the population size of capped brood remained stable. Thus, hives exhibited short-term resilience. Using a demographic matrix model, we found that the basis of resilience in dosed colonies was a substantive increase in brood initiation rate to compensate for increased brood mortality. However, computer simulation of full size colonies revealed that the increase in brood initiation led to severe reductions in colony reproduction (swarming) and long-term survival. This experiment reveals social regulatory mechanisms on colony-level that enable honeybees to partly compensate for effects on individual level.

Immunosuppression response to the neonicotinoid insecticide thiacloprid in females and males of the red mason bee Osmia bicornis L.

Solitary bees are frequently exposed to pesticides, which are considered as one of the main stress factors that may lead to population declines. A strong immune defence is vital for the fitness of bees. However, the immune system can be weakened by environmental factors that may render bees more vulnerable to parasites and pathogens. Here we demonstrate for the first time that field-realistic concentrations of the commonly used neonicotinoid insecticide thiacloprid can severely affect the immunocompetence of Osmia bicornis. In detail, males exposed to thiacloprid solutions of 200 and 555 µg/kg showed a reduction in hemocyte density. Moreover, functional aspects of the immune defence - the antimicrobial activity of the hemolymph - were impaired in males. In females, however, only a concentration of 555 µg/kg elicited similar immunosuppressive effects. Although males are smaller than females, they consumed more food solution. This leads to a 2.77 times higher exposure in males, probably explaining the different concentration thresholds observed between the sexes. In contrast to honeybees, dietary exposure to thiacloprid did not affect melanisation or wound healing in O. bicornis. Our results demonstrate that neonicotinoid insecticides can negatively affect the immunocompetence of O. bicornis, possibly leading to an impaired disease resistance capacity.

A Comparison of Wolbachia Infection Frequencies in Varroa With Prevalence of Deformed Wing Virus.

Wolbachia are widely distributed bacterial endosymbionts of arthropods and filarial nematodes. These bacteria can affect host fitness in a variety of ways, such as protecting hosts against viruses and other pathogens. Here, we investigate the possible role of Wolbachia in the prevalence of the deformed wing virus (DWV), a highly virulent pathogen of honey bees (Apis mellifera) that is transmitted by parasitic Varroa mites (Varroa destructor). About 180 Varroa mites from 18 beehives were tested for infection with Wolbachia and DWV. We first screened for Wolbachia using two standard primers (wsp and 16S rDNA), and found 26% of the mites to be positive for Wolbachia using the wsp primer and 64% of the mites to be positive using the 16S rDNA primer. Using these intermediate Wolbachia frequencies, we then tested for statistical correlations with virus infection frequencies. The analysis revealed a significant positive correlation between DWV and Wolbachia using the wsp primer, but no significant association between DWV and Wolbachia using the 16S rDNA primer. In conclusion, there is no evidence for an anti-pathogenic effect of Wolbachia in V. destructor, but weak evidence for a pro-pathogenic effect. These results encourage further examination of Wolbachia-virus interactions in Varroa mites since an increased vector competence of the mites may significantly impact disease outbreaks in honey bees.

Immunosuppression in Honeybee Queens by the Neonicotinoids Thiacloprid and Clothianidin.

Queen health is crucial to colony survival of honeybees, since reproduction and colony growth rely solely on the queen. Queen failure is considered a relevant cause of colony losses, yet few data exist concerning effects of environmental stressors on queens. Here we demonstrate for the first time that exposure to field-realistic concentrations of neonicotinoid pesticides can severely affect the immunocompetence of queens of western honeybees (Apis mellifera L.). In young queens exposed to thiacloprid (200 µg/l or 2000 µg/l) or clothianidin (10 µg/l or 50 µg/l), the total hemocyte number and the proportion of active, differentiated hemocytes was significantly reduced. Moreover, functional aspects of the immune defence namely the wound healing/melanisation response, as well as the antimicrobial activity of the hemolymph were impaired. Our results demonstrate that neonicotinoid insecticides can negatively affect the immunocompetence of queens, possibly leading to an impaired disease resistance capacity.

Temporal dynamics of whole body residues of the neonicotinoid insecticide imidacloprid in live or dead honeybees.

In cases of acute intoxication, honeybees often lay in front of their hives for several days, exposed to sunlight and weather, before a beekeeper can take a sample. Beekeepers send samples to analytical laboratories, but sometimes no residues can be detected. Temperature and sun light could influence the decrease of pesticides in bee samples and thereby residues left for analysis. Moreover, samples are usually sent via normal postal services without cooling. We investigated the temporal dynamics of whole-body residues of imidacloprid in live or dead honeybees following a single-meal dietary exposure of 41 ng/bee under various environmental conditions, such as freezing, exposure to UV light or transfer of individuals through the mail system. Immobile, "dead" looking honeybees recovered from paralysis after 48 hours. The decrease of residues in living but paralysed bees was stopped by freezing (= killing). UV light significantly reduced residues, but the mode of transport did not affect residue levels. Group feeding increased the variance of residues, which is relevant for acute oral toxicity tests. In conclusion, elapsed time after poisoning is key for detection of neonicotinoids. Freezing before mailing significantly reduced the decrease of imidacloprid residues and may increase the accuracy of laboratory analysis for pesticides.

Observation of the Mating Behavior of Honey Bee (Apis mellifera L.) Queens Using Radio-Frequency Identification (RFID): Factors Influencing the Duration and Frequency of Nuptial Flights.

We used radio-frequency identification (RFID) to record the duration and frequency of nuptial flights of honey bee queens (Apis mellifera carnica) at two mainland mating apiaries. We investigated the effect of a number of factors on flight duration and frequency: mating apiary, number of drone colonies, queen's age and temperature. We found significant differences between the two locations concerning the number of flights on the first three days. We also observed an effect of the ambient temperature, with queens flying less often but longer at high temperatures compared to lower temperatures. Increasing the number of drone colonies from 33 to 80 colonies had no effect on the duration or on the frequency of nuptial flights. Since our results agree well with the results of previous studies, we suggest RFID as an appropriate tool to investigate the mating behavior of honey bee queens.

A historical review of managed honey bee populations in Europe and the United States and the factors that may affect them.

Honey bees are a highly valued resource around the world. They are prized for their honey and wax production and depended upon for pollination of many important crops. While globally honey bee populations have been increasing, the rate of increase is not keeping pace with demand. Further, honey bee populations have not been increasing in all parts of the world, and have declined in many nations in Europe and in North America. Managed honey bee populations are influenced by many factors including diseases, parasites, pesticides, the environment, and socio-economic factors. These factors can act alone or in combination with each other. This review highlights the present day value of honey bees, followed by a detailed description of some of the historical and present day factors that influence honey bee populations, with particular emphasis on colony populations in Europe and the United States.