Varroa Populations Research Articles

The selection traits of mite non-reproduction (MNR) and Varroa sensitive hygiene (VSH) show high variance in subsequent generations and require intensive time investment to evaluate

The honey bee ectoparasite Varroa destructor is the main cause of honey bee colony losses worldwide. Over the last decades, several projects have focused on improving the robustness of Apis mellifera against this parasitic mite. Selection traits, such as mite non-reproduction (MNR) and Varroa sensitive hygiene (VSH), are favored selection factors in Varroa resistance projects. VSH is a trait where adult honey bees remove the Varroa-infested brood. During this process, the female mites are arrested in their reproductive cycle leading to a reduction of the Varroa population within the bee colony. From 2019 to 2022, 1402 queens were instrumentally inseminated with single or multiple drones in a breeding program. Colonies headed by these queens were established annually, and the MNR and VSH levels were analyzed. VSH was evaluated in response to cells artificially infested with Varroa, and colonies with high VSH values were used to generate our selected VSH stock. Despite crossing high VSH drones and queens, we measured a remarkable heterogeneity of MNR and VSH in the next generation(s), most likely due to the well-described, high recombination rate in the honey bee genome. When assessed multiple times in the same colony, great variance between measurements was observed. Detailed evaluations of daughter colonies are thus required if selection programs want to breed colonies with reliable VSH traits. This constant need to evaluate all offspring to ensure the desirable resistance traits are present results in high workloads and great expenses in selection programs. Furthermore, such large-scale breeding programs are inefficient due to high fluctuations between measurements and generations, indicating we need to develop new approaches and improved methods for assessing Varroa resistance.

Evaluation of three different bottom boards in honeybee hives for the control of Varroa destructor

IntroductionVarroa destructor stands as the primary global pest of honey bees, inflicting direct harm on bees while also acting as a vector for a multitude of viruses. Integrated pest management is widely recognized as the optimal strategy for minimizing acaricide application. Designed bottom boards that can limit the growth of the mite population by removing them from the hive and preventing their return and reinfestation of the colony show promising potential.MethodsThe aim of this study was to compare Varroa population growth by employing three different types of bottom boards. An apiary of 55 colonies was randomly divided into five groups according to the bottom board they had: 1) tubular bottom board, 2) screen bottom board, 3) sticky bottom board, 4) conventional bottom board with a permanent treatment with acaricide (positive control), and 5) conventional bottom board (negative control). Varroa infestation level in bees, colony strength (bee and brood population), and honey reserves were determined between April and December (between autumn and spring in the southern hemisphere).ResultsColonies that had sticky bottom boards had approximately 50% less Varroa infestation than colonies with conventional bottom boards at the end of the study. Varroa infestation levels did not differ significantly between the tubular, screen, and conventional bottom boards. Colony strength was similar in all groups. No differences were observed in honey production between colonies from different groups.DiscussionThe use of sticky bottom boards was the most promising board to limit Varroa population growth and prevent colonies' reinfestation. This result encourages future studies to analyze the incorporation of this strategy in integrated pest management programs.

Faster-growing parasites threaten host populations via patch-level population dynamics and higher virulence; a case study in Varroa mites (Mesostigmata: Varroidae) and honey bees (Hymenoptera: Apidae).

Honey bee parasites remain a critical challenge to management and conservation. Because managed honey bees are maintained in colonies kept in apiaries across landscapes, the study of honey bee parasites allows the investigation of spatial principles in parasite ecology and evolution. We used a controlled field experiment to study the relationship between population growth rate and virulence (colony survival) of the parasite Varroa destructor (Anderson and Trueman). We used a nested design of 10 patches (apiaries) of 14 colonies to examine the spatial scale at which Varroa population growth matters for colony survival. We tracked Varroa population size and colony survival across a full year and found that Varroa populations that grow faster in their host colonies during the spring and summer led to larger Varroa populations across the whole apiary (patch) and higher rates of neighboring colony loss. Crucially, this increased colony loss risk manifested at the patch scale, with mortality risk being related to spatial adjacency to colonies with fast-growing Varroa strains rather than with Varroa growth rate in the colony itself. Thus, within-colony population growth predicts whole-apiary virulence, demonstrating the need to consider multiple scales when investigating parasite growth-virulence relationships.

Relative impacts of Varroadestructor (Mesostigmata:Varroidae)infestation and pesticide exposure on honey bee colony health and survival in a high-intensity corn and soybean producing region in northern Iowa.

The negative effects of Varroa and pesticides on colony health and survival are among the most important concerns to beekeepers. To compare the relative contribution of Varroa, pesticides, and interactions between them on honey bee colony performance and survival, a 2-year longitudinal study was performed in corn and soybean growing areas of Iowa. Varroa infestation and pesticide content in stored pollen were measured from 3 apiaries across a gradient of corn and soybean production areas and compared to measurements of colony health and survival. Colonies were not treated for Varroa the first year, but were treated the second year, leading to reduced Varroa infestation that was associated with larger honey bee populations, increased honey production, and higher colony survival. Pesticide detections were highest in areas with high-intensity corn and soybean production treated with conventional methods. Pesticide detections were positively associated with honey bee population size in May 2015 in the intermediate conventional (IC) and intermediate organic (IO)apiaries. Varroa populations across all apiaries in October 2015 were negatively correlated with miticide and chlorpyrifos detections. Miticide detections across all apiaries and neonicotinoid detections in the IC apiary in May 2015 were higher in colonies that survived. In July 2015, colony survival was positively associated with total pesticide detections in all apiaries and chlorpyrifos exposure in the IC and high conventional (HC) apiaries. This research suggests that Varroa are a major cause of reduced colony performance and increased colony losses, and honey bees are resilient upon low to moderate pesticide detections.

Effects of summer treatments against Varroa destructor on viral load and colony performance of Apis mellifera colonies in Eastern Canada.

Despite the use of various integrated pest management strategies to control the honey bee mite, Varroa destructor, varroosis remains the most important threat to honey bee colony health in many countries. In Canada, ineffective varroa control is linked to high winter colony losses and new treatment options, such as a summer treatment, are greatly needed. In this study, a total of 135 colonies located in 6 apiaries were submitted to one of these 3 varroa treatment strategies: (i) an Apivar® fall treatment followed by an oxalic acid (OA) treatment by dripping method; (ii) same as in (i) with a summer treatment consisting of formic acid (Formic Pro™); and (iii) same as in (i) with a summer treatment consisting of slow-release OA/glycerin pads (total of 27g of OA/colony). Treatment efficacy and their effects on colony performance, mortality, varroa population, and the abundance of 6 viruses (acute bee paralysis virus [ABPV], black queen cell virus [BQCV], deformed wing virus variant A [DWV-A], deformed wing virus variant B [DWV-B], Israeli acute paralysis virus [IAPV], and Kashmir bee virus [KBV]) were assessed. We show that a strategy with a Formic Pro summer treatment tended to reduce the varroa infestation rate to below the economic fall threshold of 15 daily varroa drop, which reduced colony mortality significantly but did not reduce the prevalence or viral load of the 6 tested viruses at the colony level. A strategy with glycerin/OA pads reduced hive weight gain and the varroa infestation rate, but not below the fall threshold. A high prevalence of DWV-B was measured in all groups, which could be related to colony mortality.

Geographical distribution of pyrethroid resistance mutations in Varroa destructor across Türkiye and a European overview

Varroa destructor Anderson & Trueman (Acari: Varroidae) is of paramount significance in modern beekeeping, with infestations presenting a primary challenge that directly influences colony health, productivity, and overall apicultural sustainability. In order to control this mite, many beekeepers rely on a limited number of approved synthetic acaricides, including the pyrethroids tau-fluvalinate, flumethrin and organophosphate coumaphos. However, the excessive use of these substances has led to the widespread development of resistance in various beekeeping areas globally. In the present study, the occurrence of resistance mutations in the voltage-gated sodium channel (VGSC) and acetylcholinesterase (AChE), the target-site of pyrethroids and coumaphos, respectively, was examined in Varroa populations collected throughout the southeastern and eastern Anatolia regions of Türkiye. All Varroa samples belonged to the Korean haplotype, and a very low genetic distance was observed based on cytochrome c oxidase subunit I (COI) gene sequences. No amino acid substitutions were determined at the key residues of AChE. On the other hand, three amino acid substitutions, (L925V/I/M), previously associated with pyrethroid resistance, were identified in nearly 80% of the Turkish populations. Importantly, L925M, the dominant mutation in the USA, was detected in Turkish Varroa populations for the first time. To gain a more comprehensive perspective, we conducted a systematic analysis of the distribution of pyrethroid resistance mutations across Europe, based on the previously reported data. Varroa populations from Mediterranean countries such as Türkiye, Spain, and Greece exhibited the highest frequency of resistance mutation. Revealing the occurrence and geographical distribution of pyrethroid resistance mutations in V. destructor populations across the country will enhance the development of more efficient strategies for mite management.

Properties of essential oils absorbed on the surface of cardboard pieces after using atmospheric-pressure plasma treatments to develop long-lasting Varroa miticides in honeybees (Apis mellifera).

The ectoparasitic mite, Varroa destructor is the most serious widespread pest of managed honeybees (Apis mellifera). Several acaricide products, which include essential oils, have been proposed for mite control. In this study, we aimed to apply atmospheric-pressure plasma to modify a cardboard piece surface in order to prolong the delivery of essential oils for controlling Varroa in honeybee colonies. Absorption capacity, release rates and evaporation rates of essential oils were determined. Cardboard piece showed a higher absorption capacity of cinnamon compared to citronella and clove. Surface modification of cardboard pieces using argon plasma at different gas flow rates and treatment durations, significantly affected the absorption of clove oil. Additionally, the release rate of cinnamon, citronella and clove was significantly enhanced after argon plasma treatments. Evaporation of cinnamon was dramatically increased by plasma treatment at 6-h of incubation. The highest evaporation rate was obtained by plasma-treated cardboard piece at a gas flow rate of 0.5 Lpm for 60 s (0.2175 ± 0.0148 μl/g•h). Efficiency of plasma-treated cardboard piece, impregnated with essential oils, was also investigated for Varroa control in honeybee colonies. In the first experiment, formic acid 65% (v/v) showed the highest efficiency of 90.60% and 81.59% with the percent of mite infestation was 0.23 ± 0.13% and 0.47 ± 0.19% at 21 and 35 days, respectively after treatment. The efficacy of cardamon oil (5% (v/v)) delivered using plasma-treated cardboard pieces was 57.71% (0.70 ± 0.16% of mite infestation) at day 21 of experiment. However, the delivery of cardamon oil at the concentration of 1% and 5% (v/v) by untreated cardboard piece had 16.93% and 24.05% of efficacy to control mites. In the 2nd experiment, the application of plasma-treated cardboard pieces impregnated with 5% (v/v) clove oil induced a 38.10% reduction in the population of Varroa mites followed by 5% (v/v) of cardamon with 30% efficiency. Although, the infestation rate of Varroa in colonies was not significant different between treatments, essential oils delivered using plasma-treated cardboard pieces tended to decrease Varroa population in the treated colonies. Hence, atmospheric-pressure plasma for the modification of other materials, should be further investigated to provide alternative control treatment applications against honeybee mites.

Molecular survey of endosymbiotic bacteria in the honeybee ectoparasite Varroa destructor in Türkiye

Varroa destructor is recognized as the predominant ectoparasite affecting Western honey bees (Apis mellifera L.) globally, representing a significant threat to the sustainability of bee colonies. The bacterial community of the digestive system and body tissues of Varroa mites has been documented in previous studies, however, the diversity and prevalence of detected endosymbiotic bacteria remain limited. In this study, the existence of four commonly found endosymbiotic bacteria including Wolbachia, Cardinium, Spiroplasma, and Rickettsia was investigated in various Varroa mite populations collected from Turkish apiaries. Almost half of the sampled population was infected with at least one endosymbiotic bacteria. Wolbachia endosymbiont was detected as the most prevalent genus, observed in six populations followed by Cardinium present in three populations. Furthermore, Spiroplasma and Rickettsia endosymbionts were each detected in one sample. To our knowledge, this study provides the first molecular characterization of Cardinium endosymbionts in V. destructor. The identity of 16S rDNA sequences of Cardinium was 98.9% of the sequence of Cardinium reported from another mite species, Brevipalpus papayensis, in the NCBI database. The study contributes new insights into the endosymbiotic bacterial community of Varroa mites. Understanding the diversity and prevalence of endosymbiotic bacteria in Varroa mites could facilitate the development of targeted management strategies to control Varroa infestations and improve honeybee health.

Mite non-reproduction, recapping behavior, and hygienic behavior (freeze-kill method) linked to Varroa destructor infestation levels in selected Apis mellifera colonies.

The genetic selection of honey bees (Apis mellifera) possessing specific social hygienic behaviors offers the beekeeping industry the possibility of controlling the Varroa destructor parasite and thus reducing its dependence on acaricides. However, the links between these behavioral traits are not yet well defined, which limits genetic progress in breeding programs. We measured the following behavioral varroa resistance traits: freeze-kill brood (FKB) and pin-kill brood (PKB) assays, varroa-sensitive hygiene (VSH), pupae removal, mite non-reproduction (MNR), and recapping activity. We found 2 negative and significant relationships: 1) between the recapping of cells infested with varroa and the total number of recapped cells, and 2) between the recapping of cells infested with varroa and VSH. We also selected the best predictive model of varroa infestation levels using the "step-wise" approach based on the Akaike information criterion. Our model revealed that MNR and FKB were significantly related to the varroa population levels, with a negative relationship; recapping was significantly related to mite infestation levels, with a positive relationship. Thus, a higher MNR or FKB score was linked to lower levels of mite infestation in colonies on August 14 (prior to fall infestation treatments); a higher recapping activity was linked to a higher level of mite infestation. Recapping behavior could be a useful trait to aid the selection of varroa-resistant bee lineages.

Seasonal differences in Varroa destructor population growth in western honey bee (Apis mellifera) colonies

Varroa destructor is a major threat for apiculture worldwide. A successful approach to control this parasite must include the application of effective treatments at the correct time. To understand the effect that treatment timing has on Varroa populations at different seasons, we conducted an experiment using a dataset comprising two separate field trials over multiple years, both trials containing four apiary sites composed of 20 honey bee colonies across an area representative of north central Florida environments. Before the start of the season, colonies were treated with two acaricides simultaneously to bring the Varroa populations to ∼0.25 mites/100 bees. Following treatment, we monitored the mite populations monthly via alcohol washes. Our results show that the temporal efficacy of Varroa treatments varies across seasons. We observed that it takes about 4–5 months after treatment in winter and spring for mite populations to return to the standard economical threshold (3 mites/100 bees). Nevertheless, there is a steeper increase in mite populations (<3 months to exceed the economic threshold) after treating colonies in summer and fall. The level of infestation that leads to colony collapse and the rate of colony decline also varied by season. To our knowledge, this is the first study evaluating seasonal effects on Varroa population growth and the first model of Varroa population growth in Florida, USA. Our results serve as a foundation for Varroa treatment models, aiding beekeepers in the future as a part of a holistic approach to control this devastating honey bee parasite.

Evaluation of oxalic acid with glycerin efficacy against Varroa destructor (Varroidae): a four year assay

Beekeepers in order to control the Varroa population, apply oxalic acid (OA) by trickling, spraying, evaporating, or fumigating, onto broodless colonies for higher efficacy. Recently, a new method was developed using strips with OA and glycerin during brood-rearing periods. However, there has been little research regarding the optimum concentration of the active ingredient and the suitable solvents to reach maximum efficacy. Thus, in the present study, we applied strips with different concentrations of OA in different mixtures of glycerin, assessed the efficacy of the method throughout a 4-year experiment, and compared it with others, commonly followed by beekeepers. Among the tested concentrations of OA, the optimum was 21% (w/v) (60 g OA, 130 mL glycerin, and 100 mL water), while the presence of water made the strips more manageable. The corrected efficacy of the method ranged from 90.4% to 94.5%, despite the different climate conditions prevailing each year and the presence of brood. All the tested concentrations presented a high number of fallen mites in the first 15–18 days, as glycerin releases OA slowly into the hive. On the other hand, synthetic acaricides or other methods (fumigation, essential oils) presented a corrected efficacy range from 10.1% to 85.6%, requiring more in some formulations repetitions. No bees’ toxicity was observed in all study cases. The results showed that the application of strips with 21% (w/v) OA diluted in glycerin and water seems to be more practical, leading to a successful Varroa control even in seasons with brood presence.

Marker assisted selection for Varroa destructor resistance in New Zealand honey bees.

Varroa destructor is a honey bee (Apis mellifera) parasite identified as one of the leading causes of overwintering colony loss in New Zealand. It has been shown that a naturally occurring heritable trait, “Varroa Sensitive Hygiene” (VSH), confers an advantage to colonies by increasing behaviours that limit the survival and reproduction of Varroa mites. The SNP 9–9224292 is an adenine/guanine (A/G) polymorphism on chromosome 9 of Apis mellifera where the G allele was observed to be associated with VSH behaviour in North American honey bees. In this study, we sought to determine if selection for the G allele of SNP 9–9224292 could decrease Varroa mite infestation of New Zealand honey bee (Apis mellifera ligustica) colonies. We genotyped queens and tracked their colonies over summer before measuring Varroa levels at the point of autumn Varroa treatment. The mean Varroa population level in colonies headed by queens that carry two copies of VSH associated G allele of SNP 9–9224292 was 28.5% (P<0.05) lower compared with colonies headed by queens with two copies of non-VSH associated A alleles. Although a significant reduction in mite infestation was achieved in treatment colonies, conventional Varroa treatment was still required for adequate Varroa control. Considering the open mating of queens used and a lack of drift control in this study, this VSH SNP shows promise for marker assisted selection of New Zealand honey bees when aiming for innate Varroa control traits.

Varroa destructor resistance to tau-fluvalinate: relationship between in vitro phenotypic test and VGSC L925V mutation.

Varroa destructor is a parasitic mite of the honey bee, Apis mellifera. Its presence in colonies can lead to a collapse within a few years. The use of acaricides has become essential to manage the hive infestation. However, the repeated and possibly incorrect use of acaricide treatments, as tau-fluvalinate, has led to the development of resistance. The in vitro phenotypic test allows the proportion of susceptible or resistant individuals to be known following an exposure to an active substance. In Varroa mites, resistance to tau-fluvalinate is associated with the presence of mutations at the position 925 of the voltage-gated sodium channel (VGSC). Here, we compared the results obtained with an in vitro phenotypic test against tau-fluvalinate and those obtained with an allelic discrimination assay on 13 treated and untreated Varroa populations in France. The correlation between the phenotype and the genetic profile rate is found to be 0.89 Varroa mites having resistant phenotypic profile have a probability of 63% to present the L925V mutation (resistance detection reliability). However, 97% of the Varroa mites having the susceptible phenotype do not present the L925V mutation (susceptible detection reliability). The L925V mutation explains most of the resistance to tau-fluvalinate in V. destructor in the populations tested. However, other mutations or types of resistance may also be involved to explain the survival of Varroa mites in the phenotypic test. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Study of pyrethroid resistance mutations in populations of Varroa destructor across Spain

The Varroa destructor mite is a serious worldwide pest of honeybees that is usually controlled with pyrethroid-based acaricides. However, the intensive use of these substances over the past decades has led to the development of resistance in these mites. Here, Varroa samples collected between 2006 and 2021 from apiaries across Spain were studied to evaluate the presence of mutations producing pyrethroid resistance, particularly those in the gene encoding the voltage-gated sodium channel (VGSC). Genotyping of the IIS4-IIS5 region of this gene detected the L925V (Leucine ‘CTG’ to valine ‘GTG’) mutation at position 925 and confirmed the presence of the M918L (Methionine ‘ATG’ to Leucine ‘TTG’) mutation at position 918 in these Spanish Varroa mites. Interestingly, the M918L mutation was always found in combination with L925V, both of which were always homozygous. Over and above the high frequency of pyrethroid-resistant mutations in Spanish Varroa populations, this apparently recent association of the M918L and L925V point mutations is a combination that appears to trigger greater resistance than that produced by L925V alone.

Multiple benefits of breeding honey bees for hygienic behavior

Honey bee colonies are prone to invasion by pests and pathogens. The combination of the parasitic mite Varroa destructor (Varroa) and the multiple viruses it vectors, is a major driver of colony losses. Breeding for hygienic behavior to reduce Varroa populations is considered a sustainable way to reduce the impact of Varroa on honey bee health. However, hygienic behavior may have a cost to the health of individual bees, both in terms of viral infection risk and immune function. To determine whether selection for hygienic behavior at the colony level is associated with trade-offs in honey bee viral infection and immune function, we compared Varroa populations, viral loads, and individual immune function between honey bee colonies that were bred for high and low hygienic behavior. Specifically, we measured Varroa infestation, Deformed wing virus DWV-A, DWV-B, Acute bee paralysis virus (ABPV), and Israeli acute paralysis virus IAPV viral genome levels in bee samples from artificially inseminated queens in our bi-directional selection program for hygienic behavior in Israel. In addition, we evaluated the expression of 12 genes from the Jak-STAT, Toll, IMD and RNAi immune pathways. We found significantly lower Varroa infestation and DWV loads in highly hygienic colonies than in colonies exhibiting low hygienic behavior. In addition, workers of the hygienic colonies had significantly higher expression of the immune genes PGRP-S2 and hymenoptaecin compared to workers from low hygienic colonies. These results indicate no trade-offs in breeding for hygienic behavior. Hygienic honey bees were associated with reduced Varroa populations and reduced DWV prevalence or load at the colony level. Individual immunity of hygienic bees was increased, which could also contribute to lower virus levels, although lower Varroa levels due to social immunity presumably contributed as well. In sum, we demonstrate multiple health benefits of breeding for honey bee hygiene.

Exposure of Apis mellifera to anti-Varroa destructor formic acid treatment induces significant proteomic alterations

The parasitic mite Varroa destructor is a major threat to the health and productivity of Apis mellifera hives and induces its effect by feeding on the fat body of larvae/pupae and transmitting viruses. The effect of the anti-Varroa formic acid containing – Mite Away Quick (MAQ) strips on the proteome of A. mellifera was assessed. Samples of A. mellifera were isolated from hives one week prior to MAQ treatment, during the week of treatment and for two weeks after the end of treatment, proteins were extracted and analysed by label free quantitative proteomics. The results indicated that samples isolated during the week of treatment showed increased abundance of a range of cuticular proteins (+ 2.65 fold to + 6.64 fold) and decreased abundance of proteins that deal with xenobiotics (Cytochrome P450 subunits −11.38 fold to −2.16 fold). Interestingly some proteins associated with the oxidative phosphorylation pathway were increased in abundance (e.g., Cox5a and Cox5b) but others (e.g., Coxfa4) were decreased. The results presented here reveal that the application of MAQ strips caused a dramatic disruption to the proteome of A. mellifera, but the effect is transient and two weeks after the end of treatment the proteome has returned to resemble that of the untreated control. While MAQ strips are effective in reducing Varroa populations, the results presented here indicate they can adversely affect the proteome of A. mellifera and may contribute to the elevated stress in hives previously affected by Varroa parasitisation.

An in-hive soft sensor based on phase space features for &amp;lt;i&amp;gt;Varroa&amp;lt;/i&amp;gt; infestation level estimation and treatment need detection

Abstract. Bees are recognized as an indispensable link in the human food chain and general ecological system. Numerous threats, from pesticides to parasites, endanger bees, enlarge the burden on hive keepers, and frequently lead to hive collapse. The Varroa destructor mite is a key threat to bee keeping, and the monitoring of hive infestation levels is of major concern for effective treatment. Continuous and unobtrusive monitoring of hive infestation levels along with other vital bee hive parameters is coveted, although there is currently no explicit sensor for this task. This problem is strikingly similar to issues such as condition monitoring or Industry 4.0 tasks, and sensors and machine learning bear the promise of viable solutions (e.g., creating a soft sensor for the task). In the context of our IndusBee4.0 project, following a bottom-up approach, a modular in-hive gas sensing system, denoted as BeE-Nose, based on common metal-oxide gas sensors (in particular, the Sensirion SGP30 and the Bosch Sensortec BME680) was deployed for a substantial part of the 2020 bee season in a single colony for a single measurement campaign. The ground truth of the Varroa population size was determined by repeated conventional method application. This paper is focused on application-specific invariant feature computation for daily hive activity characterization. The results of both gas sensors for Varroa infestation level estimation (VILE) and automated treatment need detection (ATND), as a thresholded or two-class interpretation of VILE, in the order of up to 95 % are presented. Future work strives to employ a richer sensor palette and evaluation approaches for several hives over a bee season.

Pyrethroid target-site resistance mutations in populations of the honey bee parasite Varroa destructor (Acari: Varroidae) from Flanders, Belgium.

The honey bee ectoparasite Varroa destructor is considered the major threat to apiculture, as untreated colonies of Apis mellifera usually collapse within a few years. In order to control this mite, many beekeepers rely on a limited number of approved synthetic acaricides, including the pyrethroids tau-fluvalinate and flumethrin. Due to the intensive use of these products, resistance is now commonplace in many beekeeping regions across the world. In the present study, the occurrence of amino acid substitutions at residue L925 of the voltage-gate sodium channel-the pyrethroid target site-was studied in Varroa populations collected throughout Flanders, Belgium. Dose-response bioassays supported the involvement of the frequently observed L925V substitution in flumethrin resistance, resulting in a 12.64-fold increase of the LC50 in a Varroa population mostly consisting of homozygous 925V/V mites. With the presence of L925 substitutions in about four out of 10 screened apiaries, the use of pyrethroid-based varroacides in Flanders, including the recently released PolyVar® Yellow, should be carefully considered.

A gene drive does not spread easily in populations of the honey bee parasite Varroa destructor

Varroa mites (Varroa destructor) are the most significant threat to beekeeping worldwide. They are directly or indirectly responsible for millions of colony losses each year. Beekeepers are somewhat able to control varroa populations through the use of physical and chemical treatments. However, these methods range in effectiveness, can harm honey bees, can be physically demanding on the beekeeper, and do not always provide complete protection from varroa. More importantly, in some populations varroa mites have developed resistance to available acaricides. Overcoming the varroa mite problem will require novel and targeted treatment options. Here, we explore the potential of gene drive technology to control varroa. We show that spreading a neutral gene drive in varroa is possible but requires specific colony-level management practices to overcome the challenges of both inbreeding and haplodiploidy. Furthermore, continued treatment with acaricides is necessary to give a gene drive time to fix in the varroa population. Unfortunately, a gene drive that impacts female or male fertility does not spread in varroa. Therefore, we suggest that the most promising way forward is to use a gene drive which carries a toxin precursor or removes acaricide resistance alleles.

Integrated Pest Management Control of Varroa destructor (Acari: Varroidae), the Most Damaging Pest of (Apis mellifera L. (Hymenoptera: Apidae)) Colonies.

Varroa destructor is among the greatest biological threats to western honey bee (Apis mellifera L.) health worldwide. Beekeepers routinely use chemical treatments to control this parasite, though overuse and mismanagement of these treatments have led to widespread resistance in Varroa populations. Integrated Pest Management (IPM) is an ecologically based, sustainable approach to pest management that relies on a combination of control tactics that minimize environmental impacts. Herein, we provide an in-depth review of the components of IPM in a Varroa control context. These include determining economic thresholds for the mite, identification of and monitoring for Varroa, prevention strategies, and risk conscious treatments. Furthermore, we provide a detailed review of cultural, mechanical, biological, and chemical control strategies, both longstanding and emerging, used against Varroa globally. For each control type, we describe all available treatments, their efficacies against Varroa as described in the primary scientific literature, and the obstacles to their adoption. Unfortunately, reliable IPM protocols do not exist for Varroa due to the complex biology of the mite and strong reliance on chemical control by beekeepers. To encourage beekeeper adoption, a successful IPM approach to Varroa control in managed colonies must be an improvement over conventional control methods and include cost-effective treatments that can be employed readily by beekeepers. It is our intention to provide the most thorough review of Varroa control options available, ultimately framing our discussion within the context of IPM. We hope this article is a call-to-arms against the most damaging pest managed honey bee colonies face worldwide.