Prospects, challenges and perspectives in harnessing natural selection to solve the 'varroa problem' of honey bees.

Honey bees, Apis mellifera, of European origin are major pollinators of crops and wild flora. Their endemic and exported populations are threatened by a variety of abiotic and biotic factors. Among the latter, the ectoparasitic mite Varroa destructor is the most important single cause behind colony mortality. The selection of mite resistance in honey bee populations has been deemed a more sustainable solution to its control than varroacidal treatments. Because natural selection has led to the survival of some European and African honey bee populations to V. destructor infestations, harnessing its principles has recently been highlighted as a more efficient way to provide honey bee lineages that survive infestations when compared with conventional selection on resistance traits against the parasite. However, the challenges and drawbacks of harnessing natural selection to solve the varroa problem have only been minimally addressed. We argue that failing to consider these issues could lead to counterproductive results, such as increased mite virulence, loss of genetic diversity reducing host resilience, population collapses or poor acceptance by beekeepers. Therefore, it appears timely to evaluate the prospects for the success of such programmes and the qualities of the populations obtained. After reviewing the approaches proposed in the literature and their outcomes, we consider their advantages and drawbacks and propose perspectives to overcome their limitations. In these considerations, we not only reflect on the theoretical aspects of host-parasite relationships but also on the currently largely neglected practical constraints, that is, the requirements for productive beekeeping, conservation or rewilding objectives. To optimize natural selection-based programmes towards these objectives, we suggest designs based on a combination of nature-driven phenotypic differentiation and human-directed selection of traits. Such a dual strategy aims at allowing field-realistic evolutionary approaches towards the survival of V. destructor infestations and the improvement of honey bee health

1.15 Sub-lethal effects at stake: Does the acaricide Coumaphos and fungicide Folpet affect the hypopharyngeal glands size?

Background: Pesticides are increasingly suspected to be involved at a global scale in honey bee decline. Most studies focuses on acute effects on mortality, whereas sub-lethal effects are poorly understood. Hypophryngeal glands (HPG), producing royal jelly to feed brood, are established marker to assess sub-lethal effects of pesticides where for example the size of the acini can be measured. The size of the later depends of different natural factors: the age of the bee and the type of task performed by the bee. The HPG are the best developed at the age of 10 days by nursing bees. Regarding the data requirements of the new EFSA bee guidance document and the recently developed OECD larva test 237 and 239 a data GAP regarding residues of PSM in the produced Royal Jelly by pesticide exposed bees which might have an adverse impact on larva development from day 1 to day 3 is recognized. Method: The effects on the commonly and widely used varroacide coumaphos in hives and the fungicide folpet in agriculture are currently unknown. Here we measured the size of the acini of new emerged bees treated with field realistic and non-realistic doses of both substances dissolved in pollen patties fed ad libitum for nine days (N=3 cages with 20 bees in each group) and in small encaged colonies without queens. An untreated and acetone control were established. The effects of the pesticides on workers and residues in gelee royal were tested with and without brood to take into consideration variations according to the tasks performed by the bees due to labor division. . After staining HPG activity was measured as a proxy via acini size. The results will be discussed. Results: Our results may help to improve knowledge in the development and validation of methods to evaluate the risk of bees exposed to pesticides for plant protection product authorization in an appropriate and comparable way which could be consequently implemented in standardized ring-test.Background: Pesticides are increasingly suspected to be involved at a global scale in honey bee decline. Most studies focuses on acute effects on mortality, whereas sub-lethal effects are poorly understood. Hypophryngeal glands (HPG), producing royal jelly to feed brood, are established marker to assess sub-lethal effects of pesticides where for example the size of the acini can be measured. The size of the later depends of different natural factors: the age of the bee and the type of task performed by the bee. The HPG are the best developed at the age of 10 days by nursing bees. Regarding the data requirements of the new EFSA bee guidance document and the recently developed OECD larva test 237 and 239 a data GAP regarding residues of PSM in the produced Royal Jelly by pesticide exposed bees which might have an adverse impact on larva development from day 1 to day 3 is recognized. Method: The effects on the commonly and widely used varroacide coumaphos in hives and the fungicide folpet in agriculture are currently unknown. Here we measured the size of the acini of new emerged bees treated with field realistic and non-realistic doses of both substances dissolved in pollen patties fed ad libitum for nine days (N=3 cages with 20 bees in each group) and in small encaged colonies without queens. An untreated and acetone control were established. The effects of the pesticides on workers and residues in gelee royal were tested with and without brood to take into consideration variations according to the tasks performed by the bees due to labor division. . After staining HPG activity was measured as a proxy via acini size. The results will be discussed. Results: Our results may help to improve knowledge in the development and validation of methods to evaluate the risk of bees exposed to pesticides for plant protection product authorization in an appropriate and comparable way which could be consequently implemented in standardized ring-test

Atypical viral and parasitic pattern in Algerian honey bee subspecies Apis mellifera intermissa and A. m. sahariensis

International audienceAbstractUnusually high losses of honey bee colonies are reported in many regions of the world, but little data is available concerning the status of honey bee stocks in Africa. However, the situation on this continent, where beekeeping is weakly developed and where the wild population of the pollinator remains large, can give us an insight on the causes of increased mortalities elsewhere. In this study, we evaluate the health status of Apis mellifera intermissa and A. m. sahariensis populations inhabiting the north and the south of Algeria, respectively. We report few colony losses associated with an atypical pattern of prevalence for common honey bee parasites and pathogens. The presence or absence of these risk factors is discussed in relation to the occurrence of local and global colony losses to contribute to our understanding of how honey bee pathogens and parasite impact this pollinator’s health

Advances and perspectives in selecting resistance traits against the parasitic mite Varroa destructor in honey bees.

In spite of the implementation of control strategies in honey bee (Apis mellifera) keeping, the invasive parasitic mite Varroa destructor remains one of the main causes of colony losses in numerous countries. Therefore, this parasite represents a serious threat to beekeeping and agro-ecosystems that benefit from the pollination services provided by honey bees. To maintain their stocks, beekeepers have to treat their colonies with acaricides every year. Selecting lineages that are resistant to infestations is deemed to be a more sustainable approach. Over the last three decades, numerous selection programs have been initiated to improve the host-parasite relationship and to support honey bee survival in the presence of the parasite without the need for acaricide treatments. Although resistance traits have been included in the selection strategy of honey bees, it has not been possible to globally solve the V. destructor problem. In this study, we review the literature on the reasons that have potentially limited the success of such selection programs. We compile the available information to assess the relevance of selected traits and the potential environmental effects that distort trait expression and colony survival. Limitations to the implementation of these traits in the field are also discussed. Improving our knowledge of the mechanisms underlying resistance to V. destructor to increase trait relevance, optimizing selection programs to reduce environmental effects, and communicating selection outcomes are all crucial to efforts aiming at establishing a balanced relationship between the invasive parasite and its new host

The ectoparasitic mite Tropilaelaps mercedesae (Acari, Laelapidae) as a vector of honeybee viruses

Abstract.: The ectoparasitic mites Varroa destructor and Tropilaelaps mercedesae share life history traits and both infect honeybee colonies, Apis mellifera. Since V. destructor is a biological vector of several honeybee viruses, we here test whether T. mercedesae can also be infected and enable virus replication. In Kunming (China), workers and T. mercedesae mites were sampled from three A. mellifera colonies, where workers were exhibiting clinical symptoms of deformed wing virus (DWV). We analysed a pooled bee sample (15 workers) and 29 mites for the presence of Deformed wing virus (DWV), Black queen cell virus (BQCV), Sacbrood virus (SBV), Kashmir bee virus (KBV), Acute bee paralysis virus (ABPV), and Chronic bee paralysis virus (CBPV). Virus positive samples were analysed with a qPCR. Only DWV +RNA was found but with a high titre of up to 108 equivalent virus copies per mite and 106 per bee. Moreover, in all DWV positive mites (N= 12) and in the bee sample virus-RNA was also detected using RT-PCR and tagged RT-PCR, strongly suggesting virus replication. Our data show for the first time that T. mercedesae may be a biological vector of DWV, which would open a novel route of virus spread in A. mellifer

New reference genomes of honey bee-associated bacteria Paenibacillus melissococcoides, Paenibacillus dendritiformis, and Paenibacillus thiaminolyticus.

We sequenced the genomes of recently discovered Paenibacillus melissococcoides (CCOS 2000) and of the type strains of closely related P. thiaminolyticus (DSM 7262) and P. dendritiformis (LMG 21716). The three genomes set the basis to unambiguous diagnostic of these honey bee associated Paenibacillus bacteria

Molecular and phylogenetic characterization of honey bee viruses, Nosema microsporidia, protozoan parasites, and parasitic mites in China

China has the largest number of managed honey bee colonies, which produce the highest quantity of honey and royal jelly in the world; however, the presence of honey bee pathogens and parasites has never been rigorously identified in Chinese apiaries. We thus conducted a molecular survey of honey bee RNA viruses, Nosema microsporidia, protozoan parasites, and tracheal mites associated with nonnative Apis mellifera ligustica and native Apis cerana cerana colonies in China. We found the presence of black queen cell virus (BQCV), chronic bee paralysis virus (CBPV), deformed wing virus (DWV), Israeli acute paralysis virus (IAPV), and sacbrood virus (SBV), but not that of acute bee paralysis virus (ABPV) or Kashmir bee virus (KBV). DWV was the most prevalent in the tested samples. Phylogenies of Chinese viral isolates demonstrated that genetically heterogeneous populations of BQCV, CBPV, DWV, and A. cerana-infecting SBV, and relatively homogenous populations of IAPV and A. meliifera-infecting new strain of SBV with single origins, are spread in Chinese apiaries. Similar to previous observations in many countries, Nosema ceranae, but not Nosema apis, was prevalent in the tested samples. Crithidia mellificae, but not Apicystis bombi was found in five samples, including one A. c. cerana colony, demonstrating that C. mellificae is capable of infecting multiple honey bee species. Based on kinetoplast-encoded cytochrome b sequences, the C. mellificae isolate from A. c. cerana represents a novel haplotype with 19 nucleotide differences from the Chinese and Japanese isolates from A. m. ligustica. This suggests that A. c. cerana is the native host for this specific haplotype. The tracheal mite, Acarapis woodi, was detected in one A. m. ligustica colony. Our results demonstrate that honey bee RNA viruses, N. ceranae, C. mellificae, and tracheal mites are present in Chinese apiaries, and some might be originated from native Asian honey bees

Differential resistance across paternal genotypes of honey bee brood to the pathogenic bacterium Melissococcus plutonius

Melissococcus plutonius is a pathogenic bacterium affecting immature stages of the western honey bee (Apis mellifera) and leads to European foulbrood (EFB) disease. Despite EFB outbreaks increasing in frequency in several countries in recent decades, there is little knowledge on the epidemiology of M. plutonius or on the defence mechanisms of honey bees against this pathogen. Mating of honey bee queens with multiple males (polyandry) can be such a mechanism, as it has been shown to be beneficial to colony health and fitness. It is hypothesized that a high level of polyandry was selected for in response to pathogen pressure to maximize the probability that at least some patrilines among nestmates in a colony possess a high degree of resistance to specific pathogens, ultimately protecting colonies against infections. We show that M. plutonius infection provokes differential mortality among patrilines of immature honey bee workers. Such differences indicate a genetic origin of resistance against this pathogen—supporting the polyandry hypothesis—and open up avenues to improve control of EFB disease via selective breeding