Varroa Infestation Research Articles

Varroa destructor infestation levels in Africanized honey bee colonies in Brazil from 1977 when first detected to 2020

Varroa destructor infestation levels in Africanized honey bee colonies in Brazil from 1977 when first detected to 2020

Impact of nutritional and sanitary management on Apis mellifera colony dynamics and pathogen loads

Aim of study: The aim of this study was to assess the impact of the mite control strategies combined with nutritional management on honey bee colony dynamics and survival during winter, the following spring, and summer. Area of study: Santa Fe province in central Argentina. Material and methods: We set two apiaries with 40 colonies each and fed one apiary with high fructose corn syrup (HFCS) and the other with sucrose syrup (SS). Within each apiary, we treated half the colonies against Varroa mites and half of these treated colonies also received a pollen patty. The other half of the colonies remained untreated and did not received pollen patties. All colonies were sampled for Varroa infestation level, Nosema ceranae abundance and colony strength seven times during a year (from summer 2016 to autumn 2017). We computed autumn mite invasion and colony losses at each sampling time. Main results: Colonies fed with HFCS had more brood cells during the study that those fed with SS and treated colonies had fewer adult bees and Varroa infestation than untreated colonies. No significant effect of the protein supplementation was observed on any of the response variables. , SS colonies from all groups had significantly more mites drop counts than HFCS colonies. Research highlights: Considering that a reduced frequency of application is desirable, our results suggested that nutrition management could enhance chemical treatment effectiveness since honey bees might profit from improved nutrition. However, a better understanding of the nutritional requirements of the colonies under field conditions is needed.

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.

The Epidemiological Situation of the Managed Honey Bee (Apis mellifera) Colonies in the Italian Region Emilia-Romagna.

Simple SummaryThe collapse of honey bee colonies is an important phenomenon worldwide. The individual and synergic actions of pathogens are one of the causes of this decline. Monitoring programs are essential to understand and prevent the epidemiological patterns that are involved. The present study aimed to investigate the health status of honey bees in the Emilia–Romagna region (northern Italy) during the year 2021, on workers from 31 apiaries. The prevalence and abundance of DWV, KBV, ABPV, CBPV, Nosema ceranae, and trypanosomatids (Lotmaria passim, Crithidia mellificae, Crithidia bombi) were investigated four times in the year using molecular methods. Trypanosomatids were not found in any of the samples, while DWV, CBPV and N. ceranae were the most prevalent pathogens. Pathogens had different peaks in abundance over the months, showing seasonal trends related to the dynamics of both bee colonies and Varroa destructor infestation. The results of this study suggest that the monitoring program could be useful to understand the dynamics of honey bee pathogens.The recent decades witnessed the collapse of honey bee colonies at a global level. The major drivers of this collapse include both individual and synergic pathogen actions, threatening the colonies’ survival. The need to define the epidemiological pattern of the pathogens that are involved has led to the establishment of monitoring programs in many countries, Italy included. In this framework, the health status of managed honey bees in the Emilia–Romagna region (northern Italy) was assessed, throughout the year 2021, on workers from 31 apiaries to investigate the presence of major known and emerging honey bee pathogens. The prevalence and abundance of DWV, KBV, ABPV, CBPV, Nosema ceranae, and trypanosomatids (Lotmaria passim, Crithidia mellificae, Crithidia bombi) were assessed by molecular methods. The most prevalent pathogen was DWV, followed by CBPV and N. ceranae. Trypanosomatids were not found in any of the samples. Pathogens had different peaks in abundance over the months, showing seasonal trends that were related to the dynamics of both bee colonies and Varroa destructor infestation. For some of the pathogens, a weak but significant correlation was observed between abundance and geographical longitude. The information obtained in this study increases our understanding of the epidemiological situation of bee colonies in Emilia–Romagna and helps us to implement better disease prevention and improved territorial management of honey bee health.

Deep Learning Beehive Monitoring System for Early Detection of the Varroa Mite

One of the most critical causes of colony collapse disorder in beekeeping is caused by the Varroa mite. This paper presents an embedded camera module supported by a deep learning algorithm for the process of early detecting of Varroa infestations. This is achieved using a deep learning algorithm that tries to identify bees inside the brood frames carrying the mite in real-time. The end-node device camera module is placed inside the brood box. It is equipped with offline detection in remote areas of limited network coverage or online imagery data transmission and mite detection over the cloud. The proposed deep learning algorithm uses a deep learning network for bee object detection and an image processing step to identify the mite on the previously detected objects. Finally, the authors present their proof of concept experimentation of their approach that can offer a total bee and varroa detection accuracy of close to 70%. The authors present in detail and discuss their experimental results.

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.

Spatial clusters of Varroa destructor control strategies in Europe

Beekeepers have various options to control the parasitic mite Varroa destructor in honey bee colonies, but no empirical data are available on the methods they apply in practice. We surveyed 28,409 beekeepers maintaining 507,641 colonies in 30 European countries concerning Varroa control methods. The set of 19 different Varroa diagnosis and control measures was taken from the annual COLOSS questionnaire on honey bee colony losses. The most frequent activities were monitoring of Varroa infestations, drone brood removal, various oxalic acid applications and formic acid applications. Correspondence analysis and hierarchical clustering on principal components showed that six Varroa control options (not necessarily the most used ones) significantly contribute to defining three distinctive clusters of countries in terms of Varroa control in Europe. Cluster I (eight Western European countries) is characterized by use of amitraz strips. Cluster II comprises 15 countries from Scandinavia, the Baltics, and Central-Southern Europe. This cluster is characterized by long-term formic acid treatments. Cluster III is characterized by dominant usage of amitraz fumigation and formed by seven Eastern European countries. The median number of different treatments applied per beekeeper was lowest in cluster III. Based on estimation of colony numbers in included countries, we extrapolated the proportions of colonies treated with different methods in Europe. This suggests that circa 62% of colonies in Europe are treated with amitraz, followed by oxalic acid for the next largest percentage of colonies. We discuss possible factors determining the choice of Varroa control measures in the different clusters.

Honey bees metapopulations, parasites, and landscape - search for possible relationships: case study Slovakia

The loss of bees is a relatively well-known worldwide phenomenon. Many papers examine the direct influence of different factors on global bees lost. However, a look at this problem with the intentions of host-parasite-environment interactions is rare. This paper post tries to prove possible connections among bees, their parasites and landscape structure. During the research at 27 suitable sites across Slovakia, Nosema spp. spores were detected in two samples (7.41 % of examined apiaries) and Varroa destructor in a total of 41 % of samples (mean prevalence of 0.57). Significant differences were found in mites infestation in altitudes up to 500 m and over 500 m, and at sites with different ES. Considering the landscape structure, Varroa infestation was significantly positively influenced by the presence of discontinuous urban fabrics.

The payoffs and tradeoffs of hygienic behavior: a five year field study on a local population of honey bees

Honey bees are exposed to a variety of risk factors, among which the ectoparasitic mite Varroa destructor and its associated viruses are considered to be the most significant problem worldwide. It has been widely recognized that honey bee stocks resistant to mites are an essential part of any sustainable long-term management of Varroa. The aim of this study was to evaluate the efficacy of hygienic behavior in a local population of honey bees in reducing Varroa infestation. A bi-directional selection for high and low rates of hygienic behavior was carried out in Israel using either artificially inseminated or naturally mated queens. Colonies were screened for performance including population size, honey production, levels of Varroa infestation, and the level of hygienic behavior. Furthermore, we examined the costs and benefits of the selection, and possible trade-offs, using the above measurements of colony performance to ensure their productivity. The selection process revealed that the trait is heritable. The maternal phenotype has a significant effect on Varroa load, as colonies founded by hygienic daughter queens showed a significantly lower parasite load. No major trade-offs were found between the rate of hygienic behavior, honey yield, and population size. Measuring the direct benefits of hygienic behavior through colony performance suggests that breeding for this trait makes bees more resistant to Varroa destructor. These results are promising for our successful local bee breeding programs in a Mediterranean climate.

Improving the Varroa (Varroa destructor) Control Strategy by Brood Treatment with Formic Acid-A Pilot Study on Spring Applications.

Simple SummaryThe varroa mite control in a natural and sustainable way is critical for beekeeping, taking into account the importance of honey bees for pollination as well as for obtaining clean products. In recent time, new procedures for varroosis treatment in the reproductive phase were developed, which can be applied any time during the active season as they use volatile organic acids, widely accepted for organic beekeeping. Such a procedure consists of brushing the capped brood with formic acid, which is very effective in killing varroa mites but also minimally invasive for honey bee colonies. The importance of varroosis treatments before winter bee rearing is evident and widely accepted, as most of the actual treatments are limited to the late active season applications for different reasons, especially because they are focused on phoretic mites. Having in view the flexibility of the new procedure’s application in the whole period of the active season, we started a pilot study to preliminarily test the effectiveness of spring applications on varroa mite control. The results show significant differences in brood infestation between experimental and control groups, in the same apiary, which gives clear indications that spring applications could be beneficial for improving the varroa control strategies.The importance of varroosis control in a natural and sustainable way is crucial for beekeeping, having in view the varroa mite impact on honey bee health. In the last years, we developed a highly effective procedure for treating varroa in capped brood using volatile organic acids. This procedure can be applied at any moment of the active season as it uses organic substances. Taking into account the necessity to drastically reduce the level of varroa infestation in colonies before winter bee rearing, we developed a relatively simple pilot study to preliminarily test the impact of spring treatments on varroa infestation level in brood, to be evaluated in summer when, naturally, the population of mites increases. To test the hypothesis, two experimentally treated groups and a control group were used. The treatment consisted of brushing all capped brood with formic acid of 65% concentration in one and two applications. The obtained results show very significant differences between the treated and control groups in terms of infested cell percentages evaluated in the July–August period. Consequently, the spring treatments could be an important tool in limiting the varroa mite multiplication, but further experiments are necessary to test and adapt them to different local conditions.

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.

COMPARATIVE DYNAMICS OF VAROOSIS OF HONEY BEES IN UKRAINE FOR THE PERIOD 2008-2011 AND 2018-2021

Honey bees (Apis mellifera) are prone to various diseases that cause significant economic damage, the most common disease in Ukraine among bees is varroasis. The Varroa destructor mite is currently considered a major biotic threat to A. mellifera of European origin. Since infection, the tick population is growing and may lead to the loss of the bee colony in the first year of parasitism. Within the apiary varroosis leads to the manifestation of viral diseases, contributes to susceptibility to insecticide poisoning, increases material and labor costs for anti-varroa measures. The aim of the work was to study the dynamics of the epizootic process of Varroa infestation by comparing the invasiveness of the lesion over the decades in terms of 2008-2011 and 2018-2021 in the regions of Ukraine. Reference materials and methods. The material for statistical analysis was the annual reporting forms № 2-Vet "Report on the Work of State Laboratories of Veterinary Medicine" which based on generally accepted methods of diagnosing bee Varroa infestation in Ukraine. Analysis of epizootic indicators to determine the dynamics of the epizootic process of varroosis was conducted in 2008-2011 and 2018-2021. Thus, during 2008-2011, 503,241 studies were conducted, of which a positive result was obtained in 19,857 cases, the average invasiveness of bee varroosis in the period from 2008 to 2011 was 3.8 %. The level of invasiveness for this period ranged from 1.2 to 5.1 %. During the period 2018-2021, 503,166 studies were conducted, of which a positive result was obtained in 11,988 cases, the average invasiveness of bees with Varroa infestation in Ukraine for the period from 2018 to 2021 was 2.4 %. The invasiveness decrease of varroosis from 3.8 to 2.4 % is observed due to the improvement of the epizootic situation in the north and center of Ukraine such as in Kyiv, Zhytomyr, Chernihiv, Sumy, Chernivtsi, Odessa, Vinnytsia, Cherkasy, Poltava and Kharkiv regions, however, over the years the situation has deteriorated in southern Ukraine in Kherson, Zaporizhia and Donetsk regions. The laboratories of State Service of Ukraine on Food Safety and Consumer protection conducted planned studies of selected material taken from 182,740 bee colonies. A wide range of therapeutic and prophylactic drugs allows developing more effective schemes and techniques of anti-varroosis treatments of bee colonies in apiaries. However, a certain chaos and diversity of scientific and industrial research does not reduce the invasiveness of V. destructor throughout Ukraine. According to the level of invasiveness, the most affected regions of Ukraine in 2018-2021 were Volyn, Rivne, Kirovohrad, Donetsk, Zaporizhia, Kherson regions, the level of invasiveness in which is more than 4,5 %. Zakarpattia and Lviv regions remain stable in the temporarily prosperous risk zone over the years of research, where spring anti-varroosis treatments of bee colonies are carried out in order to sell bee packages. The results of research in 2018-2021 indicate a more careful attitude of beekeepers to the needs of controlling the invasiveness of bee colonies with the mite V. destructor, as well as the need for wider introduction of spring anti-varroosis treatments. The ability of SSUFSCP laboratories to conduct a huge amount of research, both at public expense and at the expense of individuals, makes a significant contribution to improving the epizootic situation with varroosis.

Understanding the Enemy: A Review of the Genetics, Behavior and Chemical Ecology of Varroa destructor, the Parasitic Mite of Apis mellifera.

Varroa destructor (Mesostigmata: Varroidae) is arguably the most damaging parasitic mite that attacks honey bees worldwide. Since its initial host switch from the Asian honey bee (Apis cerana) (Hymenoptera: Apidae) to the Western honey bee (Apis mellifera) (Hymenoptera: Apidae), Varroa has become a widely successful invasive species, attacking honey bees on almost every continent where apiculture is practiced. Two haplotypes of V. destructor (Japanese and Korean) parasitize A. mellifera, both of which vector various honey bee-associated viruses. As the population of Varroa grows within a colony in the spring and summer, so do the levels of viral infections. Not surprisingly, high Varroa parasitization impacts bees at the individual level, causing bees to exhibit lower weight, decreased learning capacity, and shorter lifespan. High levels of Varroa infestation can lead to colony-wide varroosis and eventually colony death, especially when no control measures are taken against the mites. Varroa has become a successful parasite of A. mellifera because of its ability to reproduce within both drone cells and worker cells, which allows populations to expand rapidly. Varroa uses several chemical cues to complete its life cycle, many of which remain understudied and should be further explored. Given the growing reports of pesticide resistance by Varroa in several countries, a better understanding of the mite’s basic biology is needed to find alternative pest management strategies. This review focuses on the genetics, behavior, and chemical ecology of V. destructor within A. mellifera colonies, and points to areas of research that should be exploited to better control this pervasive honey bee enemy.

Results of Annual Monitoring of Honey Bee Colony Winter Losses in Ukraine: Winter 2019–2020

Purpose. To estimate honey bee (Apis mellifera Linnaeus, 1758) colony winter loss rate for Ukraine after the winter 2019–2020 in the context of international COLOSS survey. Methods. Analysis of the results of the survey of Ukrainian beekeepers on A. mellifera colonies survival after the winter 2019-2020 by using the questionnaire developed by the coordinators of COLOSS international monitoring group. Unified approaches to data collection and statistical processing have been used. Valid protocols from 702 respondents from five physical-geographical zones of Ukraine have been analysed. Results. Honey bee colony winter loss rates for Ukraine after the winter 2019-2020 was 9.29%, the mortality rate was 5.41 %; the losses due to unsolvable queen problems – 2.19 %, and due to natural disasters – 1.69 %. The total losses in the steppe zone of Ukraine were 16.08%, significantly exceeding this indicator in the forest-steppe zone (8.94%), the zone of deciduous forests (6.73%) and the Ukrainian Carpathians (8.14%). The most common sign of dead colonies in Ukraine was the presence of a large number of dead bees in or in front of the hive (31.3 %) and unknown symptoms (37,3 %). The majority of Ukrainian beekeepers (50.7%) did not notice any difference in wintering of the colonies going into winter with a new queen in comparison with the old one. Among antivarroa drugs, the majority of respondents preferred products based on amitraz (fumigation – 50.8%, in plates – 15.7%) and flumethrin (20.0%). We confirmed statistically lower level of winter losses in colonies treated with amitraz (fumigation), whereas colonies treated with formic acid (long-term) had higher losses. Conclusions. Honey bee (Apis mellifera Linnaeus, 1758) colony winter loss rate for Ukraine after the winter 2019–2020 was 9.29% and decreased slightly compared to the last year (11.18%) and the year before last (11.26%). It was almost twice lower than the average for the countries participating in COLOSS international monitoring (18,1%) (Gray, 2021). The highest losses were observed in the steppe zone of Ukraine, whereas the lowest in the Ukrainian Carpathians. The smaller beekeeping operations with at most 50 colonies suffered significantly higher losses 12.66%) compared to medium and large ones (9.48% and 6.52%, respectively). The number of beekeepers treating colonies against varroosis was 90.6%, and all of them mentioned that they had pre-monitored the level of Varroa infestation.

Hygiene-Eliciting Brood Semiochemicals as a Tool for Assaying Honey Bee (Hymenoptera: Apidae) Colony Resistance to Varroa (Mesostigmata: Varroidae).

Despite numerous interventions, the ectoparasitic mite Varroa (Varroa destructor Anderson and Trueman [Mesostigmata: Varroidae]) and the pathogens it vectors remain a primary threat to honey bee (Apis mellifera Linnaeus [Hymenoptera: Apidae]) health. Hygienic behavior, the ability to detect, uncap, and remove unhealthy brood from the colony, has been bred for selectively for over two decades and continues to be a promising avenue for improved Varroa management. Although hygienic behavior is expressed more in Varroa-resistant colonies, hygiene does not always confer resistance to Varroa. Additionally, existing Varroa resistance selection methods trade efficacy for efficiency, because those achieving the highest levels of Varroa resistance can be time-consuming, and thus expensive and impractical for apicultural use. Here, we tested the hypothesis that hygienic response to a mixture of semiochemicals associated with Varroa-infested honey bee brood can serve as an improved tool for predicting colony-level Varroa resistance. In support of our hypothesis, we demonstrated that a mixture of the compounds (Z)-10-tritriacontene, (Z)-8-hentriacontene, (Z)-8-heptadecene, and (Z)-6-pentadecene triggers hygienic behavior in a two-hour assay, and that high-performing colonies (hygienic response to ≥60% of treated cells) have significantly lower Varroa infestations, remove significantly more introduced Varroa, and are significantly more likely to survive the winter compared to low-performing colonies (hygienic response to <60% of treated cells). We discuss the relative efficacy and efficiency of this assay for facilitating apiary management decisions and selection of Varroa-resistant honey bees, as well as the relevance of these findings to honey bee health, pollination services, and social insect communication.

Hygienic Behavior of Apis mellifera and Its Relationship with Varroa destructor Infestation and Honey Production in the Central Highlands of Ecuador.

Simple SummaryThe honey bee (Apis mellifera) is an insect that has a relevant role in natural and agricultural ecosystems due to its leading role in the pollination of crops that are part of humanity’s food chain. Even in the face of the modernization and the intensification of agriculture, the honey bee has maintained its economic importance due to the value generated by its products. At present, when attempting to improve the characteristics of bees, it is important to evaluate variables such as hygienic behavior, Varroa infestation rates, and honey production as a basis for improvement plans in search of increasing productive yields at altitudes 2600 m above sea level (m.a.s.l.). The strength of bees against parasites, and therefore the better development of their colonies, was determined, resulting in a healthy colony with an increase in honey production. The altitude and the hygienic behavior of bees in the central highlands showed an inverse relationship. There was no relationship between infestation rates and production; it is proposed that environmental factors do not modulate Varroa levels or honey production.The aim of this research was to analyze the relationship among hygienic behavior (HB), Varroa destructor infestation, and honey production in the central highlands of Ecuador. Overall, 75 honey bee colonies were evaluated before, during, and after production at three altitude levels (2600–2800, 2801–3000, and >3000 m.a.s.l.). The hygienic behavior percentage of the colonies was determined by the pin-killing method, and the colonies were classified into three groups: high HB (>85%), mid HB (60.1–85%), and low HB (≤60%). Varroa infestation was diagnosed as well, and honey production was evaluated only during production. HB was high and heterogeneous, averaging 80% ± 9.7%. Its highest expression was observed at lower altitudes. The infestation degree was low (3.47% ± 1.56%), although the mite was detected in all colonies upon sampling. A negative correlation was observed between HB and Varroa infestation in the first sampling (−0.49 **), suggesting that the high- and mid-altitude HB colonies underwent the lowest infestation rates, regardless of sampling. The correlations between HB and production were significant (0.26 *), indicating a positive effect of HB on production, meaning that colonies with high HB obtained the highest honey production (25.08 ± 4.82 kg/hive). The HB of bees showed an inverse relationship with altitude and it tended to reduce the effect of Varroa infestation, favoring honey production and, thus, suggesting the feasibility of selecting colonies with high HB.

Winter weight loss of different subspecies of honey bee Apis mellifera colonies (Linnaeus, 1758) in southwestern Sweden.

Honey bees are currently facing mounting pressures that have resulted in population declines in many parts of the world. In northern climates winter is a bottleneck for honey bees and a thorough understanding of the colonies’ ability to withstand the winter is needed in order to protect the bees from further decline. In this study the influence of weather variables on colony weight loss was studied over one winter (2019–2020) in two apiaries (32 colonies in total) in southwestern Sweden with weather stations recording wind and temperature at 5-min intervals. Three subspecies of honey bees and one hybrid were studied: the native Apis mellifera mellifera, the Italian A. m. ligustica, the Carniolan A. m. carnica and the hybrid Buckfast. Additionally, we recorded Varroa mite infestation. To analyze factors involved in resource consumption, three modelling approaches using weather and weight data were developed: the first links daily consumption rates with environmental variables, the second modelled the cumulative weight change over time, and the third estimated weight change over time taking light intensity and temperature into account. Weight losses were in general low (0.039 ± 0.013kg/day and colony) and comparable to southern locations, likely due to an exceptionally warm winter (average temperature 3.5°C). Weight losses differed only marginally between subspecies with indications that A. m. mellifera was having a more conservative resource consumption, but more studies are needed to confirm this. We did not find any effect of Varroa mite numbers on weight loss. Increased light intensity and temperature both triggered the resource consumption in honey bees. The temperature effect on resource consumption is in accordance with the metabolic theory of ecology. The consequences of these findings on honey bee survival under predicted climate changes, is still an open question that needs further analysis.

Field evaluation of Varroa-resistance traits in surviving Apis mellifera colonies in Argentina

Varroa destructor is one of the most important sanitary threats for the beekeeping industry and so far disease control is based mainly on chemical treatment. However, a long-term solution may arise from studying natural surviving colonies of Apis mellifera. We compared the Varroa infestation rate in six commercial colonies that received annual treatment against mites and six non-treated colonies that survived in absence of any treatment for the last 6years. In addition, we evaluated two potential mechanisms that might be involved in colony survival: hygienic (HYG) and Varroa-sensitive hygiene behavior (VSH) by means of pin-killed and mite artificial infestation, respectively. HYG and VSH were negatively correlated with mite infestation independently of the colony group (treated or non-treated). Furthermore, colonies expressing high levels of pupae removal (≥ 80%) showed higher %HYG and lower mite infestation compared to colonies showing low pupae removal (< 80%). The analysis of reproductive status of mites from the non-removed infested cells evidenced that more infertile mites are found in colonies with more than 80% of pupae removal. To study non-treated colonies that survive for several years, it is a suitable approach for identifying the underlying mechanisms related to Varroa-resistance.

Formic acid combined with oxalic acid to boost the acaricide efficacy against Varroa destructor in Apis mellifera

Beekeepers need reliable protocols to keep the Varroa infestation to sustainable levels. The goal of our study was to verify if a treatment consisting in the association of two organic acids, commonly used to control Varroa, could be a good strategy to boost their acaricide efficacy without affecting honey bee colonies' survival. We carried out a field trial in Central Italy with 56 colonies divided into seven homogeneous groups of 8 hives each. Honey bee colonies were treated with three different formic acid formulations: liquid formic acid (60%) administered with the Nassenheider Professional® dispenser, MAQS®, and Varterminator®. All of them were combined or not with two oxalic acid treatments (Api-Bioxal®). The mean acaricide efficacy of liquid formic acid (Nassenheider Professional®) alone was 73.2 ± 12.5%, while MAQS® and Varterminator® showed respectively a mean efficacy of 49.3 ± 14.9% and 81.2 ± 16.0%. The combination of the above mentioned treatments with oxalic acid increased the efficacy respectively to 92.7 ± 7.5% (Nassenheider Professional®); 89.5 ± 9.2% (MAQS®) and 89.4 ± 8.0% (Varterminator®). Unfortunately, the higher efficacy reflected an abnormal adult honey bees mortality with respect to the control group in Nassenheider Professional® and MAQS® groups. The combination of organic acids can boost the efficacy of treatments and reduce their variability but colonies strength should be carefully evaluated in order to avoid excessive losses.

Evaluation of total phenols content, anti-DPPH activity and the content of selected antioxidants in the honeybee drone brood homogenate

The subject of the present research is the evaluation of health-promoting properties caused by the presence of some vitamins as well as the antioxidative potential of the honeybee drone brood homogenate (DBH). The study used 139 homogenate samples obtained from various apiaries and collected over 3 years, three times during each beekeeping season. Samples differed in terms of varroa infestation, stage of brood development, location of the apiary, and the degree of environmental contamination. The content of ascorbic acid, α-tocopherol, all-trans-retinol, and coenzyme Q10 in the tested samples was determined through the application of HPLC/DAD/UV and LC/QQQ/MS methods. The antioxidant potential of samples was assessed using the Folin-Ciocalteu and DPPH methods.