There is evidence that in Europe and North America many species of pollinators are in decline, both in abundance and distribution. Although there is a long list of potential causes of this decline, there is concern that neonicotinoid insecticides, in particular through their use as seed treatments are, at least in part, responsible. This paper describes a project that set out to summarize the natural science evidence base relevant to neonicotinoid insecticides and insect pollinators in as policy-neutral terms as possible. A series of evidence statements are listed and categorized according to the nature of the underlying information. The evidence summary forms the appendix to this paper and an annotated bibliography is provided in the electronic supplementary material.
A summary is provided of recent advances in the natural science evidence base concerning the effects of neonicotinoid insecticides on insect pollinators in a format (a ‘restatement') intended to be accessible to informed but not expert policymakers and stakeholders. Important new studies have been published since our recent review of this field (Godfray et al. 2014 Proc. R. Soc. B 281, 20140558. (doi:10.1098/rspb.2014.055810.1098/rspb.2014.0558)) and the subject continues to be an area of very active research and high policy relevance.
Understanding the diversity and consequences of viruses present in honey bees is critical for maintaining pollinator health and managing the spread of disease. The viral landscape of honey bees (Apis mellifera) has changed dramatically since the emergence of the parasitic mite Varroa destructor, which increased the spread of virulent variants of viruses such as deformed wing virus. Previous genomic studies have focused on colonies suffering from infections by Varroa and virulent viruses, which could mask other viral species present in honey bees, resulting in a distorted view of viral diversity. To capture the viral diversity within colonies that are exposed to mites but do not suffer the ultimate consequences of the infestation, we examined populations of honey bees that have evolved naturally or have been selected for resistance to Varroa. This analysis revealed seven novel viruses isolated from honey bees sampled globally, including the first identification of negative-sense RNA viruses in honey bees. Notably, two rhabdoviruses were present in three geographically diverse locations and were also present in Varroa mites parasitizing the bees. To characterize the antiviral response, we performed deep sequencing of small RNA populations in honey bees and mites. This provided evidence of a Dicer-mediated immune response in honey bees, while the viral small RNA profile in Varroa mites was novel and distinct from the response observed in bees. Overall, we show that viral diversity in honey bee colonies is greater than previously thought, which encourages additional studies of the bee virome on a global scale and which may ultimately improve disease management.IMPORTANCE Honey bee populations have become increasingly susceptible to colony losses due to pathogenic viruses spread by parasitic Varroa mites. To date, 24 viruses have been described in honey bees, with most belonging to the order Picornavirales. Collapsing Varroa-infected colonies are often overwhelmed with high levels of picornaviruses. To examine the underlying viral diversity in honey bees, we employed viral metatranscriptomics analyses on three geographically diverse Varroa-resistant populations from Europe, Africa, and the Pacific. We describe seven novel viruses from a range of diverse viral families, including two viruses that are present in all three locations. In honey bees, small RNA sequences indicate that these viruses are processed by Dicer and the RNA interference pathway, whereas Varroa mites produce strikingly novel small RNA patterns. This work increases the number and diversity of known honey bee viruses and will ultimately contribute to improved disease management in our most important agricultural pollinator.
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 parasitic mite Varroa destructor is a serious threat for western honey bee colonies and beekeepers are compelled to control it to keep their colonies healthy. Yet, by controlling varroa no resistance to the parasite can evolve. As a trial, honey bee colonies have been left untreated in isolated locations to allow development of resistance or tolerance to the mite. These colonies developed an ability to live without control measures against varroa, although the traits responsible for this resistance or tolerance are still unclear. Two of these resistant populations have been studied to test the involvement of specific varroa mite targeted hygienic behaviour varroa sensitive hygiene (VSH) in the acquired resistance. Individual mites were manually introduced into just capped brood cells, after which the brood combs were placed in colonies of the two resistant populations and in control colonies in which varroa had always been controlled. We followed the development of the mites, including possible removals. We found that VSH had increased strongly in one of the selections, up to 40% of the infested cells with mites and pupae were removed, but it had decreased in the other selection, compared to the control colonies. Further we could not conclude from our data that VSH only or preferentially targets reproducing mites, leaving non-reproducing mites undisturbed. The different VSH responses between the two selected resistant honey bee populations lead to conclude that more than one mechanism of resistance may evolve in response to the selection pressure by varroa mites. La higiene sensible a Varroa contribuye a la resistencia a varroa naturalmente seleccionada en abejas melíferas El ácaro parásito Varroa destructor es una seria amenaza para las colonias occidentales de abejas melíferas y los apicultores se ven obligados a controlarlo para mantener sus colonias sanas. Sin embargo, al controlar la varroa no puede evolucionar hacia ninguna resistencia al parásito. Como ensayo, se han dejado sin tratar colonias de abejas en lugares aislados para permitir el desarrollo de resistencia o tolerancia al ácaro. Estas colonias desarrollaron una capacidad para vivir sin medidas de control contra la varroa, aunque los rasgos responsables de esta resistencia o tolerancia aún no están claros. Dos de estas poblaciones resistentes han sido estudiadas para probar la implicació n de una varroa específica con un comportamiento higiénico específico sensible a varroa (VSH por sus siglas en inglés) en la resistencia adquirida. Los ácaros individuales se introdujeron manualmente en celdas de cría recién operculadas, después de lo cual los cuadros de cría se colocaron en colonias de las dos poblaciones resistentes y en colonias de control en las que la varroa siempre se había controlado. Seguimos el desarrollo de los ácaros, incluyendo posibles retiradas. Se encontró que el carácter VSH había aumentado fuertemente en una de las seleccionadas, hasta el 40% de las celdas infestadas con ácaros y pupas fueron eliminadas, pero había disminuido e...
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