Bees are subject to numerous pressures in the modern world. The abundance and diversity of flowers has declined, bees are chronically exposed to cocktails of agrochemicals, and they are simultaneously exposed to novel parasites accidentally spread by humans. Climate change is likely to exacerbate these problems in the future. Stressors do not act in isolation; for example pesticide exposure can impair both detoxification mechanisms and immune responses, rendering bees more susceptible to parasites. It seems certain that chronic exposure to multiple, interacting stressors is driving honey bee colony losses and declines of wild pollinators, but such interactions are not addressed by current regulatory procedures and studying these interactions experimentally poses a major challenge. In the meantime, taking steps to reduce stress on bees would seem prudent; incorporating flower-rich habitat into farmland, reducing pesticide use through adopting more sustainable farming methods, and enforcing effective quarantine measures on bee movements are all practical measures that should be adopted. Effective monitoring of wild pollinator populations is urgently needed to inform management strategies into the future.

https://science.sciencemag.org/content/sci/early/2015/02/25/science.1255957.full.pdf

Bee declines driven by combined stress from parasites, pesticides, and lack of flowers

http://www.tsusinvasives.org/dotAsset/3b275f2a-205c-4012-b48a-038a13dddf8f.pdf

Biology and control of Varroa destructor

Large-scale losses of honey bee colonies represent a poorly understood problem of global importance. Both biotic and abiotic factors are involved in this phenomenon that is often associated with high loads of parasites and pathogens. A stronger impact of pathogens in honey bees exposed to neonicotinoid insecticides has been reported, but the causal link between insecticide exposure and the possible immune alteration of honey bees remains elusive. Here, we demonstrate that the neonicotinoid insecticide clothianidin negatively modulates NF-κB immune signaling in insects and adversely affects honey bee antiviral defenses controlled by this transcription factor. We have identified in insects a negative modulator of NF-κB activation, which is a leucine-rich repeat protein. Exposure to clothianidin, by enhancing the transcription of the gene encoding this inhibitor, reduces immune defenses and promotes the replication of the deformed wing virus in honey bees bearing covert infections. This honey bee immunosuppression is similarly induced by a different neonicotinoid, imidacloprid, but not by the organophosphate chlorpyriphos, which does not affect NF-κB signaling. The occurrence at sublethal doses of this insecticide-induced viral proliferation suggests that the studied neonicotinoids might have a negative effect at the field level. Our experiments uncover a further level of regulation of the immune response in insects and set the stage for studies on neural modulation of immunity in animals. Furthermore, this study has implications for the conservation of bees, as it will contribute to the definition of more appropriate guidelines for testing chronic or sublethal effects of pesticides used in agriculture.

/pdf/neonicotinoid-clothianidin-adversely-affects-insect-immunity-krj99prmvb.pdf

Neonicotinoid clothianidin adversely affects insect immunity and promotes replication of a viral pathogen in honey bees

SummaryVery rapidly after Varroa destructor invaded apiaries of Apis mellifera, the devastating effect of this mite prompted an active research effort to understand and control this parasite. Over a few decades, varroa has spread to most countries exploiting A. mellifera. As a consequence, a large number of teams have worked with this organism, developing a diversity of research methods. Often different approaches have been followed to achieve the same goal. The diversity of methods made the results difficult to compare, thus hindering our understanding of this parasite. In this paper, we provide easy to use protocols for the collection, identification, diagnosis, rearing, breeding, marking and measurement of infestation rates and fertility of V. destructor. We also describe experimental protocols to study orientation and feeding of the mite, to infest colonies or cells and measure the mite's susceptibility to acaricides. Where relevant, we describe which mite should be used for bioassays since their beha...

Standard methods for varroa research

https://s3-eu-west-1.amazonaws.com/hsd-sites/biodling/nyheter/are_bee_diseases_linked_to_pesticides.pdf

Are bee diseases linked to pesticides? - A brief review.

The health of the honeybee and, indirectly, global crop production are threatened by several biotic and abiotic factors, which play a poorly defined role in the induction of widespread colony losses. Recent descriptive studies suggest that colony losses are often related to the interaction between pathogens and other stress factors, including parasites. Through an integrated analysis of the population and molecular changes associated with the collapse of honeybee colonies infested by the parasitic mite Varroa destructor, we show that this parasite can de-stabilise the within-host dynamics of Deformed wing virus (DWV), transforming a cryptic and vertically transmitted virus into a rapidly replicating killer, which attains lethal levels late in the season. The de-stabilisation of DWV infection is associated with an immunosuppression syndrome, characterized by a strong down-regulation of the transcription factor NF-κB. The centrality of NF-κB in host responses to a range of environmental challenges suggests that this transcription factor can act as a common currency underlying colony collapse that may be triggered by different causes. Our results offer an integrated account for the multifactorial origin of honeybee losses and a new framework for assessing, and possibly mitigating, the impact of environmental challenges on honeybee health.

/pdf/synergistic-parasite-pathogen-interactions-mediated-by-host-1dy0dk7pf8.pdf

Synergistic parasite-pathogen interactions mediated by host immunity can drive the collapse of honeybee colonies.

Hygienic behaviour of bees towards mite infested brood is involved in the tolerance of some bee strains to Varroa destructor. The stimuli triggering hygienic behaviour are olfactory cues emanating from cells containing infested brood but their identity is still unknown. After confirming the capacity of bees to detect and empty mite-infested cells, we studied the volatile chemicals released by artificially infested worker brood cells by means of SPME-GC-MS. The identified chemicals were then bioassayed by comparing the bees' hygienic behaviour towards treated cells into which 1 µg of each compound was injected and control cells which received the solvent alone. Z-(6)-pentadecene significantly increased the number of cells emptied by the bees. Varroa destructor / semiochemicals / hygienic behaviour / removal / hydrocarbons

/pdf/a-semiochemical-from-brood-cells-infested-by-varroa-2hnfxwxpkv.pdf

A semiochemical from brood cells infested by Varroa destructor triggers hygienic behaviour in Apis mellifera

The reversion of resistance to pyrethroids in Varroa destructor Anderson & Trueman was studied in Friuli (northern Italy), where resistance was detected in 1995 and pyrethroids had not been used since. Mites were sampled in seven localities each year between 1997 and 2000 and assayed in the laboratory for the resistance to fluvalinate by using paraffin coated capsules. Survival at the diagnostic concentration, expected to kill all susceptible mites (200 mg/kg), decreased in all the localities by about ten times in three years, from 19-66% to 1.3-7.8%. Thus, the disadvantage associated with the resistance to pyrethroids in V. destructor is small, as usual when resistance is due to monooxygenases. Its impact on the selection of resistant mites during annual application of treatments is negligible; appreciable effects of reversion can be expected only over many generations of the mite. Varroa destructor / reversion / resistance / pyrethroids

/pdf/decline-in-the-proportion-of-mites-resistant-to-fluvalinate-14z6b5pjce.pdf

Decline in the proportion of mites resistant to fluvalinate in a population of Varroa destructor not treated with pyrethroids

The mite Varroa destructor Anderson & Trueman is a parasite of the honeybee Apis mellifera L. and represents a major threat for apiculture in the Western world. Reproduction takes place only inside bee brood cells that are invaded just before sealing; drone cells are preferred over worker cells, whereas queen cells are not normally invaded. Lower incidence of mites in queen cells is at least partly due to the deterrent activity of royal jelly. In this study, the repellent properties of royal jelly were investigated using a lab bioassay. Chemical analysis showed that octanoic acid is a major volatile component of royal jelly; by contrast, the concentration is much lower in drone and worker larval food. Bioassays, carried out under lab conditions, demonstrated that octanoic acid is repellent to the mite. Field studies in bee colonies confirmed that the compound may interfere with the process of cell invasion by the mite.

Octanoic acid confers to royal jelly varroa-repellent properties.

Chemical stimuli responsible for the biological activity of bee larval food on Varroa destructor were studied both in the laboratory and under natural conditions. Loss of activity after neutralization and air entrainment experiments suggested that active substances were acidic and volatile. Linear, branched and aromatic carboxy-acids, as well as hydroxy-acids, were identified by GC-MS and SPME-GC-MS analysis in organic larval food extracts. The low molecular weight carboxy-acids identified were tested in a laboratory assay using a four-well arena. All the acids tested were inactive with the exception of 2- hydroxyhexanoic acid; comparison with related compounds and dose-response studies confirmed the activity of this acid at 10 and 100 ng per well showing that this is a semiochemical for the mite. One hundred nanograms of 2-hydroxyhexanoic acid applied to worker brood cells before capping increased by 36% the number of mites per cell in the treated brood compared to the control cells. 2-Hydroxyhexanoic acid / cell invasion / larval food / semiochemical / Varroa destructor

/pdf/a-semiochemical-from-larval-food-influences-the-entrance-of-qyv6f00cj2.pdf

Giorgio Della Vedova

Papers

Synergistic parasite-pathogen interactions mediated by host immunity can drive the collapse of honeybee colonies.

A semiochemical from brood cells infested by Varroa destructor triggers hygienic behaviour in Apis mellifera

Decline in the proportion of mites resistant to fluvalinate in a population of Varroa destructor not treated with pyrethroids

Octanoic acid confers to royal jelly varroa-repellent properties.

A semiochemical from larval food influences the entrance of Varroa destructor into brood cells