The influence of brood comb cell size on the reproductive behavior of the ectoparasitic mite Varroa destructor in Africanized honey bee colonies

Africanized honey bees (Apis mellifera, Hymenoptera: Apidae) in Brazil are tolerant of infestations with the exotic ectoparasitic mite, Varroa destructor (Mesostigmata: Varroidae), while the European honey bees used in apiculture throughout most of the world are severely affected. Africanized honey bees are normally kept in hives with both naturally built small width brood cells and with brood cells made from European-sized foundation, yet we know that comb cell size has an effect on varroa reproductive behavior. Three types (sizes) of brood combs were placed in each of six Africanized honey bee colonies: new (self-built) Africanized comb, new Italian comb (that the bees made from Italian-sized commercial foundation), and new Carniolan comb (built naturally by Carniolan bees). About 100 cells of each type were analyzed in each colony. The Africanized comb cells were significantly smaller in (inner) width (4.84 mm) than the European-sized comb cells (5.16 and 5.27 mm for Italian and Carniolan cells, respectively). The brood cell infestation rates (percentage cells infested) were significantly higher in the Carniolan-sized comb cells (19.3%) than in the Italian and Africanized cells (13.9 and 10.3%, respectively). The Carniolan-sized cells also had a significantly larger number of invading adult female mites per 100 brood cells (24.4) than did the Italian-sized cells (17.7) and the natural-sized Africanized worker brood cells (15.6). European-sized worker brood cells were always more infested than the Africanized worker brood cells in the same colony. There was a highly significant correlation (P<0.01) between cell width and the rate of infestation with varroa in four of the six colonies. The small width comb cells produced by Africanized honey bees may have a role in the ability of these bees to tolerate infestations by Varroa destructor, furthermore it appears that natural-sized comb cells are superior to over-sized comb cells for disease resistance.     

Acaricide treatment affects viral dynamics in Varroa destructor-infested honey bee colonies via both host physiology and mite control

Honey bee (Apis mellifera) colonies are declining, and a number of stressors have been identified that affect, alone or in combination, the health of honey bees. The ectoparasitic mite Varroa destructor, honey bee viruses that are often closely associated with the mite, and pesticides used to control the mite population form a complex system of stressors that may affect honey bee health in different ways. During an acaricide treatment using Apistan (plastic strips coated with tau-fluvalinate), we analyzed the infection dynamics of deformed wing virus (DWV), sacbrood virus (SBV), and black queen cell virus (BQCV) in adult bees, mite-infested pupae, their associated Varroa mites, and uninfested pupae, comparing these to similar samples from untreated control colonies. Titers of DWV increased initially with the onset of the acaricide application and then slightly decreased progressively coinciding with the removal of the Varroa mite infestation. This initial increase in DWV titers suggests a physiological effect of tau-fluvalinate on the host's susceptibility to viral infection. DWV titers in adult bees and uninfested pupae remained higher in treated colonies than in untreated colonies. The titers of SBV and BQCV did not show any direct relationship with mite infestation and showed a variety of possible effects of the acaricide treatment. The results indicate that other factors besides Varroa mite infestation may be important to the development and maintenance of damaging DWV titers in colonies. Possible biochemical explanations for the observed synergistic effects between tau-fluvalinate and virus infections are discussed.     

蜜蜂瓦螨敏感卫生行为研究进展

蜜蜂具有很高的生态价值和经济价值,对农业生产帮助巨大。然而,狄斯瓦螨Varroa destructor寄生给西方蜜蜂Apis mellifera蜂群造成重大损失,对蜜蜂健康构成严重威胁,因此,狄斯瓦螨的防治变得尤为紧要。虽然化学防治是防治狄斯瓦螨常用且有效措施,但仍存在许多缺点,如造成蜂产品污染、导致蜂螨产生抗药性等。另一方面,培育抗螨蜂种被证明是可持续的狄斯瓦螨防治方法。瓦螨敏感卫生行为(Varroa sensitive hygiene, VSH)是蜜蜂重要的抗螨性状之一。本文从狄斯瓦螨的生活周期、对蜜蜂的危害、蜜蜂抗螨行为、瓦螨敏感卫生行为调控和遗传育种等方面进行综述,为狄斯瓦螨防治和抗螨蜂种选育提供参考。     

Varroa-tolerant Italian honey bees introduced from Brazil were not more efficient in defending themselves against the mite Varroa destructor than Carniolan bees in Germany

In Europe and North America honey bees cannot be kept without chemical treatments against Varroa destructor. Nevertheless, in Brazil an isolated population of Italian honey bees has been kept on an island since 1984 without treatment against this mite. The infestation rates in these colonies have decreased over the years. We looked for possible varroa-tolerance factors in six Italian honey bee colonies prepared with queens from this Brazilian island population, compared to six Carniolan colonies, both tested at the same site in Germany. One such factor was the percentage of damaged mites in the colony debris, which has been reported as an indicator of colony tolerance to varroa. A mean of 35.8% of the varroa mites collected from the bottoms of the Italian bee colonies were found damaged, among which 19.1% were still alive. A significantly greater proportion of damaged mites were found in the Carniolan bees (42.3%) and 22.5% were collected alive. The most frequent kind of damage found was damaged legs alone, affecting 47.4% of the mites collected from debris in Italian bees, which was similar to the amount found in Carniolan colonies (46%). The mean infestation rate by the varroa mite in the worker brood cells in the Italian bee colonies was 3.9% in June and 3.5% in July, and in drone brood cells it was 19.3% in June. In the Carniolan honey bee colonies the mean infestation rates in worker brood cells were 3.0 and 6.7%, respectively in the months of June and July and 19.7% in drone brood cells in June. In conclusion, the 'Varroa-tolerant' Italian honey bees introduced from Brazil produced lower percentages of damaged mites (Varroa destructor) in hive debris and had similar brood infestation rates when compared to 'susceptible' Carniolan bees in Germany. In spite of the apparent adaptation of this population of Italian bees in Brazil, we found no indication of superiority of these bees when we examined the proportions of damaged mites and the varroa-infestation rates, compared to Carniloan bees kept in the same apiary in Germany.     

Genotypic variability and relationships between mite infestation levels, mite damage, grooming intensity, and removal of Varroa destructor mites in selected strains of worker honey bees (Apis mellifera L.)

The objective of this study was to demonstrate genotypic variability and analyze the relationships between the infestation levels of the parasitic mite Varroa destructor in honey bee (Apis mellifera) colonies, the rate of damage of fallen mites, and the intensity with which bees of different genotypes groom themselves to remove mites from their bodies. Sets of paired genotypes that are presumably susceptible and resistant to the varroa mite were compared at the colony level for number of mites falling on sticky papers and for proportion of damaged mites. They were also compared at the individual level for intensity of grooming and mite removal success. Bees from the "resistant" colonies had lower mite population rates (up to 15 fold) and higher percentages of damaged mites (up to 9 fold) than bees from the "susceptible" genotypes. At the individual level, bees from the "resistant" genotypes performed significantly more instances of intense grooming (up to 4 fold), and a significantly higher number of mites were dislodged from the bees' bodies by intense grooming than by light grooming (up to 7 fold) in all genotypes. The odds of mite removal were high and significant for all "resistant" genotypes when compared with the "susceptible" genotypes. The results of this study strongly suggest that grooming behavior and the intensity with which bees perform it, is an important component in the resistance of some honey bee genotypes to the growth of varroa mite populations. The implications of these results are discussed.     

Nitric oxide level, protein oxidation and antioxidant enzymes in rats infected by Trypanosoma evansi

The acaricidal (miticidal) activity of 90% ethanolic extracts of leaves and stem bark of Swietenia mahogani and Swietenia macrophylla were tested against Varroa destructor mite. Four concentrations were used over two different time intervals under laboratory and field conditions. In general, it was noticed that the acaricidal effect based on mortality and LC(50) of all tested extracts against the Varroa mite was concentration and time dependant. The acaricidal action against Varroa mites was relatively the least for the S. macrophylla stem bark extract at 500 ppm concentration after 48 h while it reached 100% and 95% in case of S. mahogani bark and S. macrophylla leaves, respectively. The% infestation with Varroa in colonies treated with the different extracts at various time intervals showed that the rate of infestation decreased to 0.0% after 12 days from the beginning of treatments with 500 ppm of S. mahogani leaves extract compared to 0.79% decrease after treatment with Mitac, a reference drug (60 mg/colony). The rate of infestation in case of treatments with S. mahogani bark, S. macrophylla leaves and S. macrophylla bark was decreased to 0.11%, 2.41% and 1.08%, respectively. The highest reduction was observed with S. mahogani leaves extract followed by S. mahogani bark. All the tested extracts showed less or no effect on honey bees at the different concentrations and at different bioassay times. This study suggested that the use of natural plant extracts or their products as ecofriendly biodegradable agents could be of high value for the control of Varroa mite.     

Comparative reproduction of <Emphasis Type="Italic">Varroa destructor</Emphasis> in different types of Russian and Italian honey bee combs

Earlier studies showed that Russian honey bees support slow growth of varroa mite population. We studied whether or not comb type influenced varroa reproduction in both Russian and Italian honey bees, and whether Russian bees produced comb which inhibited varroa reproduction. The major differences found in this study concerned honey bee type. Overall, the Russian honey bees had lower (2.44 ± 0.18%) levels of varroa infestation than Italian honey bees (7.20 ± 0.60%). This decreased infestation resulted in part from a reduced number of viable female offspring per foundress in the Russian (0.85 ± 0.04 female) compared to the Italian (1.23 ± 0.04 females) honey bee colonies. In addition, there was an effect by the comb built by the Russian honey bee colonies that reduced varroa reproduction. When comparing combs having Russian or Italian colony origins, Russian honey bee colonies had more non-reproducing foundress mites and fewer viable female offspring in Russian honey bee comb. This difference did not occur in Italian colonies. The age of comb in this study had mixed effects. Older comb produced similar responses for six of the seven varroa infestation parameters measured. In colonies of Italian honey bees, the older comb (2001 dark) had fewer (1.13 ± 0.07 females) viable female offspring per foundress than were found in the 2002 new (1.21 ± 0.06 females) and 1980s new (1.36 ± 0.08 females) combs. This difference did not occur with Russian honey bee colonies where the number of viable female offspring was low in all three types of combs. This study suggests that honey bee type largely influences growth of varroa mite population in a colony.     

Russian honey bee (Hymenoptera: Apidae) colonies: Acarapis woodi (Acari: Tarsonemidae) infestations and overwintering survival

Honey bee, Apis mellifera L. (Hymenoptera: Apidae), colonies infested by parasitic mites are more prone to suffer from a variety of stresses, including cold temperature. We evaluated the overwintering ability of candidate breeder lines of Russian honey bees, most of which are resistant to both Varroa destructor Anderson & Trueman and Acarapis woodi (Rennie), during 1999-2001. Our results indicate that Russian honey bee colonies (headed by original and supersedure queens) can successfully overwinter in the north, even during adverse weather conditions, owing to their frugal use of food stores and their resistance to tracheal mite infestations. In contrast, colonies of Italian honey bees consumed more food, had more mites, and lost more adult bees than Russian honey bees, even during unusually mild winter conditions.     

Resistance of the honey bee, Apis mellifera to the acarian parasite Varroa destructor: behavioural and electroantennographic data

Abstract. One way in which Apis mellifera honey bees resist Varroa destructor is by detection and elimination of nestmates. This study uses behavioural tests and electroanntennography to assess the role of chemostimuli in recognition by honey bees of this acarian ectoparasite. Behavioural tests using living or dead parasites involved observation of honey bee grooming activity (antennation) under controlled conditions in Petri dishes, and removal behaviour (uncapping and elimination of parasitized and unparasitized control brood cells) under natural conditions. Some bees from colonies with both small and large parasite populations showed aggressive behaviour (biting). No difference was observed according to whether the mite was dead or alive. Under natural conditions, bees uncapped more parasitized cells than control cells. Electroantennographic tests were performed to measure sensitivity to various Varroa extracts at three concentrations (10, 20 and 30 Varroa Equivalents). Only 30 Varroa Equivalent methanol extracts made from Varroa collected from brood cells elicited significantly greater antennal response than controls (pure solvent). All three methanol extracts elicited significantly greater antennal response than controls. No response was observed using Varroa extracts made with acetone or hexane. These findings suggest that polar products may act as chemostimuli for recognition of V. destructor by honey bees. Further study will be necessary to determine which polar products are involved in this recognition and assess grooming and removal behaviour using these products.     

Three QTL in the honey bee Apis mellifera L. suppress reproduction of the parasitic mite Varroa destructor

Varroa destructor is a highly virulent ectoparasitic mite of the honey bee Apis mellifera and a major cause of colony losses for global apiculture. Typically, chemical treatment is essential to control the parasite population in the honey bee colony. Nevertheless a few honey bee populations survive mite infestation without any treatment. We used one such Varroa mite tolerant honey bee lineage from the island of Gotland, Sweden, to identify quantitative trait loci (QTL) controlling reduced mite reproduction. We crossed a queen from this tolerant population with drones from susceptible colonies to rear hybrid queens. Two hybrid queens were used to produce a mapping population of haploid drones. We discriminated drone pupae with and without mite reproduction, and screened the genome for potential QTL using a total of 216 heterozygous microsatellite markers in a bulk segregant analysis. Subsequently, we fine mapped three candidate target regions on chromosomes 4, 7, and 9. Although the individual effect of these three QTL was found to be relatively small, the set of all three had significant impact on suppression of V. destructor reproduction by epistasis. Although it is in principle possible to use these loci for marker-assisted selection, the strong epistatic effects between the three loci complicate selective breeding programs with the Gotland Varroa tolerant honey bee stock.     

蜜蜂抗狄斯瓦螨机制的研究进展

狄斯瓦螨Varroa destructor已蔓延至世界各地,给养蜂生产带来巨大挑战,被认为是世界养蜂业的主要威胁。因此,抗螨机制的研究和抗螨蜂种的培育显得尤为重要,而掌握蜜蜂的抗螨机制则是成功培育抗螨蜂种的前提条件。本文从行为、生理及分子机制等多个不同角度对国内外蜜蜂抗狄斯瓦螨机制研究的最新进展进行了详细的阐述。尤其是从分子水平研究蜜蜂的抗螨机制对选育抗螨蜂种具有重要意义,将为利用分子遗传辅助标记筛选方法和先进的生物工程技术并结合传统的育种手段成功培育出具有抗螨性能的优良蜜蜂品系奠定基础。     

Uncapping activity of Apis mellifera L. (Hymenoptera: Apidae) towards worker brood cells infested with the mite Varroa destructor Anderson & Treuman (Mesostigmata: Varroidae)

Varroosis, a disease caused by the mite Varroa destructor Anderson and Treuman has killed hundreds of thousands of Apis mellifera L. colonies in various parts of the world. Nevertheless, the damage caused by this mite varies with the type of bee and climate conditions. Varroa causes little damage to Africanized bee colonies in Brazil, as the infestation rates are relatively stable and low. We evaluated the hygienic behavior (uncapping and removal of brood) of highly hygienic Africanized bees using combs with worker brood cells infested (naturally) and no infested with V. destructor. The daily uncapping rate, measured in eight colonies during six days, was 3.5 fold higher in the combs infested with varroa compared to no infested combs. The results show that the Africanized bees are able to recognise and remove brood cells naturally infested with V. destructor what is an important mechanism for tolerance against varroa.     

Development of a 44K SNP assay focussing on the analysis of a varroa-specific defence behaviour in honey bees (Apis mellifera carnica)

Honey bees are exposed to a number of damaging pathogens and parasites. The most destructive among them, affecting mainly the brood, is Varroa destructor. A promising approach to prevent its spread is to breed for Varroa-tolerant honey bees. A trait that has been shown to provide significant resistance against the Varroa mite is hygienic behaviour, a behavioural response of honey bee workers to brood diseases in general. This study reports the development of a 44K SNP assay, specifically designed for the analysis of hygienic behaviour of individual worker bees (Apis mellifera carnica) directed against V. destructor. Initially, 70,000 SNPs chosen from a large set of SNPs published by the Honey Bee Genome Project were validated for their suitability in the analysis of the Varroa resistance trait 'uncapping of Varroa-infested brood'. This was achieved by genotyping of pooled DNA samples of trait bearers and two trait-negative controls using next-generation sequencing. Approximately 36,000 of these validated SNPs and another 8000 SNPs not validated in this study were selected for the construction of a SNP assay. This assay will be employed in following experiments to analyse individualized DNA samples in order to identify quantitative trait loci (QTL) involved in the control of the investigated trait and to evaluate and possibly confirm QTL found in other studies. However, this assay is not just suitable to study Varroa tolerance, it is as well applicable to analyse any other trait in honey bees. In addition, because of its high density, this assay provides access into genomic selection with respect to several traits considered in honey bee breeding. It will become publicly available via AROS Applied Biotechnology AS, Aarhus, Denmark, before the end of the year 2011.     

Acute contact toxicity of oxalic acid to Varroa destructor (Acari: Varroidae) and their Apis mellifera (Hymenoptera: Apidae) hosts in laboratory bioassays

Laboratory bioassays were performed to characterize the acute contact toxicity of oxalic acid (OA) to Varroa destructor (Anderson and Trueman) and their honey bee hosts (Apis mellifera L.). Specifically, glass-vial residual bioassays were conducted to determine the lethal concentration of OA for V. destructor, and topical applications of OA in acetone were conducted to determine the lethal dose for honey bees. The results indicate that OA has a low acute toxicity to honey bees and a high acute toxicity to mites. The toxicity data will help guide scientists in delivering optimum dosages of OA to the parasite and its host, and will be useful in making treatment recommendations. The data will also facilitate future comparisons of toxicity if mite resistance to OA becomes evident.     

Effect of some characters on the population growth of mite Varroa jacobsoni in Apis mellifera L colonies and results of a bi-directional selection

Two lines of honey bees ( Apis mellifera ligustica ) were selectively propagated by instrumental insemination using the population growth of the Varroa mite as a criteria. Different infestation rates are at least partially genetic since selection produced significant bi-directional differences between lines over a period of three subsequent generations. There was no correlation between several behavioural and physiological characteristics which are potentially associated with Varroa resistance (hygienic behaviour, physical damage to mites, infertility of the intruding mites) and the development of the Varroa population after artificial infestation. There was a positive significant correlation between the total mites in the colonies and the amount of reared brood. Colony infestation was also positively correlated with the amount of honey harvested.     

Altered physiology in worker honey bees (Hymenoptera: Apidae) infested with the mite Varroa destructor (Acari: Varroidae): a factor in colony loss during overwintering?

The ectoparasitic mite Varroa destructor (Anderson & Trueman) is the most destructive pest of the honey bee, Apis mellifera L., in Europe and the United States. In temperate zones, the main losses of colonies from the mites occur during colony overwintering. To obtain a deeper knowledge of this phenomenon, we studied the mites' impact on the vitellogenin titer, the total protein stores in the hemolymph, the hemocyte characteristics, and the ecdysteroid titer of adult honey bees. These physiological characteristics are indicators of long-time survival and endocrine function, and we show that they change if bees have been infested by mites during the pupal stage. Compared with noninfested workers, adult bees infested as pupae do not fully develop physiological features typical of long-lived wintering bees. Management procedures designed to kill V. destructor in late autumn may thus fail to prevent losses of colonies because many of the adult bees are no longer able to survive until spring. Beekeepers in temperate climates should therefore combine late autumn management strategies with treatment protocols that keep the mite population at low levels before and during the period when the winter bees emerge.     

Single and dual parasitic mite infestations on the honey bee, Apis mellifera L.

Summary: The onset of foraging, proportion of pollen collectors, and weight of pollen loads were compared in individual honey bees (Apis mellifera) infested by zero, one (Acarapis woodi, the honey bee tracheal mite, or Varroa jacobsoni,varroa), or both species of parasitic mites. Phoretic varroa host choice also was compared between bees with and without tracheal mites, and tracheal mite infestation of hosts was compared between bees parasitized or not by varroa during development. The proportion of pollen collectors was not significantly different between treatments, but bees parasitized by both mites had significantly smaller pollen loads than uninfested bees. Mean onset of foraging was earliest for bees parasitized by varroa during development, 15.9 days. Bees with tracheal mites began foraging latest, at 20.5 days, and foraging ages were intermediate in bees with no mites and both, 17.6 and 18.0 days respectively. Phoretic varroa were found equally on bees with and without tracheal mite infestations, but bees parasitized by varroa during development were almost twice as likely to have tracheal mite infestations as bees with no varroa parasitism, 63.9 % and 35.5 %, respectively. These results indicate that these two parasites can have a biological interaction at the level of individual bees that is detrimental to their host colonies.     

微孢子虫和狄斯瓦螨分别侵染后的意蜂血淋巴蛋白质含量变化

微孢子虫Nosema apis和狄斯瓦螨微孢子虫Nosema apis和狄斯瓦螨 Varroa destructor (Acari: Varroidae)均为危害意蜂Apis mellifera的重要寄生虫,该文对其危害后意蜂血淋巴蛋白质含量的变化进行了研究。用考马斯亮蓝法测定了意蜂受侵染后血淋巴的蛋白质总量,并用高压超薄层等电点聚焦法进行血淋巴蛋白质分类。结果显示,病蜂血淋巴蛋白质总量,在人工感染微孢子虫后1～10天呈微孢子虫Nosema apis和狄斯瓦螨 Varroa destructor (Acari: Varroidae)均为危害意蜂Apis mellifera的重要寄生虫,该文对其危害后意蜂血淋巴蛋白质含量的变化进行了研究。用考马斯亮蓝法测定了意蜂受侵染后血淋巴的蛋白质总量,并用高压超薄层等电点聚焦法进行血淋巴蛋白质分类。结果显示,病蜂血淋巴蛋白质总量,在人工感染微孢子虫后1～10天呈上升趋势,然后逐渐下降,感染后12～27天保持在感染前意蜂血淋巴总蛋白质含量水平以下。螨侵染后意蜂血淋巴蛋白质含量明显增高,与健康意蜂相比差异极显著。高压超薄层等电点聚焦分析表明：狄斯瓦螨自然侵染意蜂后,意蜂血淋巴蛋白质组分与健康对照组相比发生了明显改变。这些结果提示,意蜂对于微孢子虫或狄斯瓦螨的侵染产生了一定的免疫反应。     

Predictive markers of honey bee colony collapse

Across the Northern hemisphere, managed honey bee colonies, Apis mellifera, are currently affected by abrupt depopulation during winter and many factors are suspected to be involved, either alone or in combination. Parasites and pathogens are considered as principal actors, in particular the ectoparasitic mite Varroa destructor, associated viruses and the microsporidian Nosema ceranae. Here we used long term monitoring of colonies and screening for eleven disease agents and genes involved in bee immunity and physiology to identify predictive markers of honeybee colony losses during winter. The data show that DWV, Nosema ceranae, Varroa destructor and Vitellogenin can be predictive markers for winter colony losses, but their predictive power strongly depends on the season. In particular, the data support that V. destructor is a key player for losses, arguably in line with its specific impact on the health of individual bees and colonies.