BackgroundRecent elevated winter loss of honey bee colonies is a major concern. The presence of the mite Varroa destructor in colonies places an important pressure on bee health. V. destructor shortens the lifespan of individual bees, while long lifespan during winter is a primary requirement to survive until the next spring. We investigated in two subsequent years the effects of different levels of V. destructor infestation during the transition from short-lived summer bees to long-lived winter bees on the lifespan of individual bees and the survival of bee colonies during winter. Colonies treated earlier in the season to reduce V. destructor infestation during the development of winter bees were expected to have longer bee lifespan and higher colony survival after winter.Methodology/Principal FindingsMite infestation was reduced using acaricide treatments during different months (July, August, September, or not treated). We found that the number of capped brood cells decreased drastically between August and November, while at the same time, the lifespan of the bees (marked cohorts) increased indicating the transition to winter bees. Low V. destructor infestation levels before and during the transition to winter bees resulted in an increase in lifespan of bees and higher colony survival compared to colonies that were not treated and that had higher infestation levels. A variety of stress-related factors could have contributed to the variation in longevity and winter survival that we found between years.Conclusions/SignificanceThis study contributes to theory about the multiple causes for the recent elevated colony losses in honey bees. Our study shows the correlation between long lifespan of winter bees and colony loss in spring. Moreover, we show that colonies treated earlier in the season had reduced V. destructor infestation during the development of winter bees resulting in longer bee lifespan and higher colony survival after winter.

The occurrence of summer heat waves is predicted to increase in amplitude and frequency in the near future, but the consequences of such extreme events are largely unknown, especially for belowground organisms. Soil organisms usually exhibit strong vertical stratification, resulting in more frequent exposure to extreme temperatures for surface-dwelling species than for soil-dwelling species. Therefore soil-dwelling species are expected to have poor acclimation responses to cope with temperature changes. We used five species of surface-dwelling and four species of soil-dwelling Collembola that habituate different depths in the soil. We tested for differences in tolerance to extreme temperatures after acclimation to warm and cold conditions. We also tested for differences in acclimation of the underlying physiology by looking at changes in membrane lipid composition. Chill coma recovery time, heat knockdown time and fatty acid profiles were determined after 1 week of acclimation to either 5 or 20 °C. Our results showed that surface-dwelling Collembola better maintained increased heat tolerance across acclimation temperatures, but no such response was found for cold tolerance. Concordantly, four of the five surface-dwelling Collembola showed up to fourfold changes in relative abundance of fatty acids after 1 week of acclimation, whereas none of the soil-dwelling species showed a significant adjustment in fatty acid composition. Strong physiological responses to temperature fluctuations may have become redundant in soil-dwelling species due to the relative thermal stability of their subterranean habitat. Based on the results of the four species studied, we expect that unless soil-dwelling species can temporarily retreat to avoid extreme temperatures, the predicted increase in heat waves under climatic change renders these soil-dwelling species more vulnerable to extinction than species with better physiological capabilities. Being able to act under a larger thermal range is probably costly and could reduce maximum performance at the optimal temperature.

Current high losses of honeybees seriously threaten crop pollination. Whereas parasite exposure is acknowledged as an important cause of these losses, the role of insecticides is controversial. Parasites and neonicotinoid insecticides reduce homing success of foragers (e.g. by reduced orientation), but it is unknown whether they negatively affect flight capacity. We investigated how exposing colonies to the parasitic mite Varroa destructor and the neonicotinoid insecticide imidacloprid affect flight capacity of foragers. Flight distance, time and speed of foragers were measured in flight mills to assess the relative and interactive effects of high V. destructor load and a field-realistic, chronic sub-lethal dose of imidacloprid. Foragers from colonies exposed to high levels of V. destructor flew shorter distances, with a larger effect when also exposed to imidacloprid. Bee body mass partly explained our results as bees were heavier when exposed to these stressors, possibly due to an earlier onset of foraging. Our findings contribute to understanding of interacting stressors that can explain colony losses. Reduced flight capacity decreases the food-collecting ability of honeybees and may hamper the use of precocious foraging as a coping mechanism during colony (nutritional) stress. Ineffective coping mechanisms may lead to destructive cascading effects and subsequent colony collapse.

SummaryIn this article we provide guidelines on statistical design and analysis of data for all kinds of honey bee research. Guidelines and selection of different methods presented are, at least partly, based on experience. This article can be used: to identify the most suitable analysis for the type of data collected; to optimise one's experimental design based on the experimental factors to be investigated, samples to be analysed, and the type of data produced; to determine how, where, and when to sample bees from colonies; or just to inspire. Also included are guidelines on presentation and reporting of data, as well as where to find help and which types of software could be useful. Guia estadistica para estudios en Apis mellifera ResumenEn este trabajo se proporcionan directrices sobre el diseño estadístico y el análisis de datos para todo tipo de investigación sobre abejas.Tanto las directrices como la selección de los diferentes métodos que se presentan están basadas, al menos en parte, en la experiencia. Este artículo se puede utilizar: para identificar el análisis más adecuado para el tipo de datos recogidos; para optimizar el diseño experimental basado en los factores experimentales a ser investigados, las muestras a analizar, y el tipo de datos que se producen; para determinar cómo, dónde , y cuando muestras abejas de las colonias, o simplemente para inspirar. También se incluyen directrices para la presentación y comunicación de los datos, así como dónde encontrar ayuda y distintos software que puedan ser útiles.

No abstract

No abstract

The ectoparasitic mite Varroa destructor is an important cause of high colony losses of the honey bee Apis mellifera. In The Netherlands, two resistant A. mellifera populations developed naturally after ceasing varroa control. As a result, mite infestation levels of the colonies of these populations are generally between 5-10%. However, the mechanisms behind mite resistance are still unclear. Since grooming behavior is a typical resistance trait that occurs in A. mellifera, we compared grooming between colonies of these two resistant populations and control colonies that had been treated against varroa twice a year in previous years. Grooming was investigated by measuring mite fall in broodless colonies in the field and in small cages with a fixed number of mites and bees in the lab. Furthermore, grooming was investigated at the individual level by measuring the effectiveness to remove dust by individual bees from the resistant and control colonies. We found that the grooming behavior of resistant colonies was unexpectedly equally or even less effective than that of control colonies. These results were supported by the effectiveness of individual bees to remove dust. Based on our results, we discuss that the trigger for grooming behavior may be density-dependent: grooming may be only beneficial at high mite infestation levels. Other resistance mechanisms than grooming are more likely to explain the varroa resistance of our two populations. Colonias de abejas (Apis mellifera) seleccionadas naturalmente por su resistencia a Varroa destructor no se acicalan más intensamente El ácaro ectoparasitario Varroa destructor es una importante causa de grandes pérdidas de colmenas de la abeja de la miel Apis mellifera. En los Países Bajos, dos poblaciones resistentes de A. mellifera se desarrollaron naturalmente después de cesar el control de varroa. Como resultado, los niveles de infestació n de ácaros en las colonias de estas poblaciones generalmente están entre el 5-10%. Sin embargo, los mecanismos que hay detrás de la resistencia del ácaro todavía no están claros. Dado que el comportamiento de acicalamiento o "grooming" es un rasgo típico de resistencia que sucede en A. mellifera, comparamos este comportamiento entre colonias de estas dos poblaciones resistentes y colonias control que habían sido tratadas contra varroa dos veces al año durante los años anteriores. El "grooming" se investigó calculando la caída de ácaros en colonias sin cría en el campo y en pequeñas cajas con un número fijo de ácaros y abejas en el laboratorio. Además, el "grooming" se investigó al nivel individual calculando la efectividad para eliminar el polvo por abejas individuales de las colonias resistentes y del control. Se encontró que el "grooming" de las colonias resistentes era inesperadamente igual o incluso menos eficaz que el de las colonias control. Estos resultados fueron apoyados por la efectividad de las abejas individuales para eliminar el polvo. Basándonos en nuestros resultados, discutimos que el desencadenante del "grooming" puede s...

Citation: van Dooremalen, C., B. Cornelissen, C. Poleij-Hok-Ahin, and T. Blacqui ere. 2018. Single and interactive effects of Varroa destructor, Nosema spp., and imidacloprid on honey bee colonies (Apis mellifera). Ecosphere 9(8):Abstract. High losses of honey bee colonies in recent decades are of great societal and economical concern and experienced as a sign of the vulnerability of the environment, including the service of crop pollination, and of the beekeeping sector. There is no single cause for the colony losses, but many contributing stressors may act in concert. Varroa destructor infestation is acknowledged as an important cause of these losses. The roles of infestation by Nosema ceranae or exposure to insecticides are controversial. Interactions between exposure to pesticides and V. destructor or Nosema spp. have previously been implicated. In two years of field experiments, we studied the effects of and possible interactions between the stressors V. destructor infestation, Nosema spp. infestation, and chronic sublethal exposure to a field-realistic dose of the insecticide imidacloprid on the performance and survival of honey bee colonies. Colonies highly infested by V. destructor were 13% smaller in size and were 59.1 times more likely to die than colonies infested with low levels of V. destructor. Infestation with high levels of Nosema sp. led to 2% decrease in size and 1.4 times higher likelihood to die compared to colonies with low levels of Nosema sp. No effects of chronic sublethal exposure to imidacloprid on colony size or survival were found in this study. Exposure to V. destructor and imidacloprid led to a slightly higher fraction of bees infested with Nosema sp., but in contrast to the expectations, no resulting interactions were found for colony size or survival. Colonies as a superorganism may well be able to compensate at the colony level for sublethal negative effects of stressors on their individuals. In our experimental study under field-realistic exposure to stressors, V. destructor was by far the most lethal one for honey bee colonies.