Resistance to amitraz in the parasitic honey bee mite Varroa destructor is associated with mutations in the β-adrenergic-like octopamine receptor

Varroa destructor is considered a major reason for high loss rate of Western honey bee (Apis mellifera) colonies. To prevent colony losses caused by V. destructor, it is necessary to actively manage the mite population. Beekeepers, particularly commercial beekeepers, have few alternative treatments other than synthetic acaricides to control the parasite, resulting in intensive treatment regimens that led to the evolution of resistance in mite populations. To investigate the mechanism of the resistance to amitraz detected in V. destructor mites from French and U.S. apiaries, we identified and characterized octopamine and tyramine receptors (the known targets of amitraz) in this species. The comparison of sequences obtained from mites collected from different apiaries with different treatment regimens, showed that the amino acid substitutions N87S or Y215H in the OctβR were associated with treatment failures reported in French or U.S. apiaries, respectively. Based on our findings, we have developed and tested two high throughput diagnostic assays based on TaqMan technology able to accurately detect mites carrying the mutations in this receptor. This valuable information may be of help for beekeepers when selecting the most suitable acaricide to manage V. destructor.

Honey bee colony losses in Brazil in 2018-2019

A research was conducted to assess honey bee colony losses in Brazil, including their likely causes. Beekeepers responded to two complete annual questionnaires (n=268 in 2018 and n=254 in 2019). There was a total of 175,003 hives of Africanized honey bees (Apis mellifera Linnaeus), (µ=335 hives per beekeeper, min=9 and Max=3,600), of which 27.2% were lost. A Generalized Linear Model (GLM) for total loss (TL) and a Wald method for average loss (AL) were used to estimate 95% confidence intervals (CI) for loss rates based on year: 2018, TL=30.5%, CI (28.5-32.4), AL=39.5, CI (37.0-41.9); and 2019, TL=23.8%, CI (22.5-25.2), AL=31.3%, CI (29.5-33.1). Pesticides were speculated to be the leading cause of colony losses (47.3%), followed by climate (drought, flood, rain: 11.6%), malnutrition (lack of flowering, lack of energy and/or protein source, wrong nutrition: 9.7%), absconding (10.2%), mismanagement (wrong migratory activity, migration to mangrove, beekeeper’s personal problems: 7.9%), predators (3.9%), queen problems (2.8%), and varroa (1.6%). Other parasites, theft, toxic pollen (Brazilian sacbrood) and bushfires accounted for the remaining 5% of losses. Due to tropical temperatures, there is no substantial winter loss. In contrast, the highest incidence of losses occurred from September to January, coinciding with the intense agricultural activity. In summary, according to participants, there were significantly higher losses in 2018 compared to 2019, with pesticides alleged to be the main cause of honey bee colony losses in Brazil. However, beekeepers usually multiply colonies during the following season, sustaining pollination and honey production, thereby supporting agricultural activity.

The distribution and population dynamics of the honey bee pathogens Crithidia mellificae and Lotmaria passim in New Zealand

<p>The honey bee Apis mellifera is experiencing colony losses across the world, this is not the first time in history colony losses have been reported. New molecular detection methods such as real-time PCR allow the detection and analysis of pathogens present in colonies, quickly and reliably. Of the pathogens that the honey bee is host to, trypanosomes are one of the least understood and trypanosome interactions within the honey bee host remain largely unknown. Using the bumble bee as a model for this host-parasite relationship. The trypanosome C. bombi is known to cause a reduced ability to gain nutrients from food and an overall decrease in efficiency of queens in founding colonies in spring. These negative correlations are significant enough in the bumble bee to warrant investigation into trypanosomes in the honey bee. The trypanosome C. mellificae was first described in the honey bee in 1967. A screening study in 2009 included a test for and detected the trypanosome in modern honey bee samples. In 2013 C. mellificae was identified as a contributory factor to overwintering colony losses when co-infected with N. ceranae. Following studies detected trypanosomes and led to the characterisation of a new species, L. passim in 2013. Lotmaria passim was first detected in New Zealand in 2014 however no subsequent studies had been undertaken to identify the distribution and dynamics of trypanosomes in New Zealand honey bee colonies. My goal in this study was to identify the presence of trypanosomes in New Zealand. In an overview study of 47 honey bee colonies from across New Zealand, 46 were positive for the L. passim species. Identified by sequencing of the GAPDH gene. A yearlong study of 15 colonies revealed that the infection rate of L. passim was consistent throughout the year and very low genetic variation was detected. Lotmaria passim was detected in all parts of New Zealand sampled in this study and often in high levels. A positive correlation was detected when L. passim was present in addition to N. apis. There was no detection of C. mellificae in my study. The lack of detection of C. mellificae may suggest that the species is not present, or that it is in such low levels it cannot yet be detected. In parallel to this trypanosome study two Nosema spp. and DWV were also examined. Nosema apis was found to be more prevalent than N. ceranae, which was not present in any South Island samples. A strong positive correlation was detected between the two Nosema spp. DWV showed a high level of variation likely a reflection of differing Varroa management practices in apiaries in this study. This study of trypanosomes is the first of its kind in New Zealand identifying the presence and population dynamics of L. passim. This in conjunction with data on Nosema spp. and DWV will be of value to the New Zealand apiculture industry and contribute to global honey bee health studies.</p>

The distribution and population dynamics of the honey bee pathogens Crithidia mellificae and Lotmaria passim in New Zealand

<p>The honey bee Apis mellifera is experiencing colony losses across the world, this is not the first time in history colony losses have been reported. New molecular detection methods such as real-time PCR allow the detection and analysis of pathogens present in colonies, quickly and reliably. Of the pathogens that the honey bee is host to, trypanosomes are one of the least understood and trypanosome interactions within the honey bee host remain largely unknown. Using the bumble bee as a model for this host-parasite relationship. The trypanosome C. bombi is known to cause a reduced ability to gain nutrients from food and an overall decrease in efficiency of queens in founding colonies in spring. These negative correlations are significant enough in the bumble bee to warrant investigation into trypanosomes in the honey bee. The trypanosome C. mellificae was first described in the honey bee in 1967. A screening study in 2009 included a test for and detected the trypanosome in modern honey bee samples. In 2013 C. mellificae was identified as a contributory factor to overwintering colony losses when co-infected with N. ceranae. Following studies detected trypanosomes and led to the characterisation of a new species, L. passim in 2013. Lotmaria passim was first detected in New Zealand in 2014 however no subsequent studies had been undertaken to identify the distribution and dynamics of trypanosomes in New Zealand honey bee colonies. My goal in this study was to identify the presence of trypanosomes in New Zealand. In an overview study of 47 honey bee colonies from across New Zealand, 46 were positive for the L. passim species. Identified by sequencing of the GAPDH gene. A yearlong study of 15 colonies revealed that the infection rate of L. passim was consistent throughout the year and very low genetic variation was detected. Lotmaria passim was detected in all parts of New Zealand sampled in this study and often in high levels. A positive correlation was detected when L. passim was present in addition to N. apis. There was no detection of C. mellificae in my study. The lack of detection of C. mellificae may suggest that the species is not present, or that it is in such low levels it cannot yet be detected. In parallel to this trypanosome study two Nosema spp. and DWV were also examined. Nosema apis was found to be more prevalent than N. ceranae, which was not present in any South Island samples. A strong positive correlation was detected between the two Nosema spp. DWV showed a high level of variation likely a reflection of differing Varroa management practices in apiaries in this study. This study of trypanosomes is the first of its kind in New Zealand identifying the presence and population dynamics of L. passim. This in conjunction with data on Nosema spp. and DWV will be of value to the New Zealand apiculture industry and contribute to global honey bee health studies.</p>

Raised seasonal temperatures reinforce autumn Varroa destructor infestation in honey bee colonies

Varroa destructor is the main pest of the honey bee Apis mellifera, causing colony losses. We investigated the effect of temperature on the autumn abundance of V. destructor in bee colonies over 1991–2020 in Central Europe. We tested the hypothesis that temperature can affect autumn mite populations with different time-lags modulating the bee abundance and brood availability. We showed that raised spring (March–May) and autumn (October) temperatures reinforce autumn V. destructor infestation in the bee colonies. The critical temperature signals embrace periods of bee activity, i.e., just after the first cleansing flights and just before the last observed bee flights, but no direct effects of phenological changes on V. destructor abundance were found. These effects were potentially associated with increased bee reproduction in the specific periods of the year and not with the extended period of activity or accelerated spring onset. We found significant effects of autumn bee abundance, autumn capped brood abundance, and the number of colonies merged on autumn mite infestation. We also observed differences in V. destructor abundance between bees derived from different subspecies. We indicated that climatic effects, through influence on the bee abundance and brood availability, are one of the main drivers regulating V. destructor abundance.

Identifying the climatic drivers of honey bee disease in England and Wales

Honey bee colony health has received considerable attention in recent years, with many studies highlighting multifactorial issues contributing to colony losses. Disease and weather are consistently highlighted as primary drivers of colony loss, yet little is understood about how they interact. Here, we combined disease records from government honey bee health inspections with meteorological data from the CEDA to identify how weather impacts EFB, AFB, CBP, varroosis, chalkbrood and sacbrood. Using R-INLA, we determined how different meteorological variables influenced disease prevalence and disease risk. Temperature caused an increase in the risk of both varroosis and sacbrood, but overall, the weather had a varying effect on the six honey bee diseases. The risk of disease was also spatially varied and was impacted by the meteorological variables. These results are an important step in identifying the impacts of climate change on honey bees and honey bee diseases.

A biophysical approach to assess weather impacts on honey bee colony winter mortality

The western honey bee ( Apis mellifera ) is one of the most important insects kept by humans, but high colony losses are reported around the world. While the effects of general climatic conditions on colony winter mortality were already demonstrated, no study has investigated specific weather conditions linked to biophysical processes governing colony vitality. Here, we quantify the comparative relevance of four such processes that co-determine the colonies' fitness for wintering during the annual hive management cycle, using a 10-year dataset of winter colony mortality in Austria that includes 266 378 bee colonies. We formulate four process-based hypotheses for wintering success and operationalize them with weather indicators. The empirical data is used to fit simple and multiple linear regression models on different geographical scales. The results show that approximately 20% of winter mortality variability can be explained by the analysed weather conditions, and that it is most sensitive to the duration of extreme cold spells in mid and late winter. Our approach shows the potential of developing weather indicators based on biophysical processes and discusses the way forward for applying them in climate change studies.

Resistance to amitraz in the parasitic honey bee mite Varroa destructor is associated with mutations in the β-adrenergic-like octopamine receptor

Varroa destructor is considered a major reason for high loss rate of Western honey bee (Apis mellifera) colonies. To prevent colony losses caused by V. destructor it is necessary to actively manage the mite population. Beekeepers, particularly commercial beekeepers, have few alternative treatments other than synthetic acaricides to control the parasite, resulting in intensive treatment regimens that led to the evolution of resistance in mite populations. To investigate the mechanism of the resistance to amitraz detected in V. destructor mites from French and U.S. apiaries, we identified and characterized octopamine and tyramine receptors (the known targets of amitraz) in this species. The comparison of sequences obtained from mites collected from different apiaries with different treatment regimens, showed that the amino acid substitutions N87S or Y215H in the OctβR were associated with treatment failures reported in French or U.S. apiaries, respectively. Based on our findings, we have developed and tested two high throughput diagnostic assays based on TaqMan® able to accurately detect mites carrying the mutations in this receptor. This valuable information may be of help for beekeepers when selecting the most suitable acaricide to manage V. destructor.

The interaction between a parasite and sub-optimal temperatures contributes to honey bee decline

Global insect decline and, in particular, honey bee colony losses are related to multiple stress factors, including landscape deterioration, pollution, parasites and climate change. However, the implications of the interaction among different stress factors for insect health are still poorly understood; in particular, little is known on how challenging environmental conditions can influence the impact of parasites. Here we exploited the honey bee as a model system to approach this problem and carried out extensive lab and field work aiming at assessing how suboptimal temperatures and parasitic challenges can alter the homeostatic balance of individual bees and the whole colony, leading to individual death and colony collapse. We found that mite infestation further than increasing the mortality of bees, induces an anorexia that in turn reduces the capacity of bees to thermoregulate, thus exposing them to the detrimental effect of lower temperatures. This, in turn, has dramatic implications for the colony as a whole. The results highlight the important role that abiotic factors can have in shaping the effect of parasitic challenges on honey bees. Furthermore, the multilevel and holistic approach adopted here can represent a useful template for similar studies on other insect species, which are particularly urgent in view of climate change and the continuous pressure of natural and exotic parasites on insect populations.

First come, first served: superinfection exclusion in Deformed wing virus is dependent upon sequence identity and not the order of virus acquisition

Deformed wing virus (DWV) is the most important globally distributed pathogen of honey bees and, when vectored by the ectoparasite Varroa destructor, is associated with high levels of colony losses. Divergent DWV types may differ in their pathogenicity and are reported to exhibit superinfection exclusion upon sequential infections, an inevitability in a Varroa-infested colony. We used a reverse genetic approach to investigate competition and interactions between genetically distinct or related virus strains, analysing viral load over time, tissue distribution with reporter gene-expressing viruses and recombination between virus variants. Transient competition occurred irrespective of the order of virus acquisition, indicating no directionality or dominance. Over longer periods, the ability to compete with a pre-existing infection correlated with the genetic divergence of the inoculae. Genetic recombination was observed throughout the DWV genome with recombinants accounting for ~2% of the population as determined by deep sequencing. We propose that superinfection exclusion, if it occurs at all, is a consequence of a cross-reactive RNAi response to the viruses involved, explaining the lack of dominance of one virus type over another. A better understanding of the consequences of dual- and superinfection will inform development of cross-protective honey bee vaccines and landscape-scale DWV transmission and evolution.