Varroa destructor infestation in untreated honey bee (Hymenoptera: Apidae) colonies selected for hygienic behavior

Honey bee (Apis mellifera L.) colonies bred for hygienic behavior were tested in a large field trial to determine if they were able to resist the parasitic mite Varroa destructor better than unselected colonies of"Starline" stock. Colonies bred for hygienic behavior are able to detect, uncap, and remove experimentally infested brood from the nest, although the extent to which the behavior actually reduces the overall mite-load in untreated, naturally infested colonies needed further verification. The results indicate that hygienic colonies with queens mated naturally to unselected drones had significantly fewer mites on adult bees and within worker brood cells than Starline colonies for up to 1 yr without treatment in a commercial, migratory beekeeping operation. Hygienic colonies actively defended themselves against the mites when mite levels were relatively low. At high mite infestations (>15% of worker brood and of adult bees), the majority of hygienic colonies required treatment to prevent collapse. Overall, the hygienic colonies had similar adult populations and brood areas, produced as much honey, and had less brood disease than the Starline colonies. Thus, honey bees bred for hygienic behavior performed as well if not better than other commercial lines of bees and maintained lower mite loads for up to one year without treatment.     

香精油的抗蜂螨作用及其在蜂群中的应用

香精油及其组分具有显著的抗螨效果。研究者通过筛选试验测定了多种香精油及其组分的抗螨能力,多数在实验室中表现出良好的抗螨效果,但除了百里酚及其混合物外,很少在野外试验中表现出强抗螨能力。百里酚及其混合物的抑螨率超过了90%,对蜜蜂危害较小,长期使用后残留量很低。很有必要对香精油的抗蜂螨作用作进一步的研究,同时结合其它防治手段,建立一套全面的害虫防治策略,以控制蜂螨的危害。     

蜜蜂寄生螨—狄斯瓦螨的研究进展

狄斯瓦螨Varroa destructor是对世界养蜂业危害最大的蜜蜂寄生虫,严重危害蜜蜂封盖幼虫、蛹和成蜂,并携带和传播蜜蜂病毒,造成蜂群生产力严重下降乃至全群毁灭。狄斯瓦螨的有效防治措施的研发有赖于对其研究进展的了解,本文综述了以下3方面的研究概况:1)狄斯瓦螨的繁殖特性;2)对蜜蜂的危害;3)主要防治方法。以期为蜂螨相关的研究和应用奠定基础。     

Effects of Imidacloprid and Varroa destructor on survival and health of European honey bees,Apis mellifera

There has been growing concern over declines in populations of honey bees and other pollinators which are a vital part to our food security. It is imperative to identify factors responsible for accelerated declines in bee populations and develop solutions for reversing bee losses. While exact causes of colony losses remain elusive, risk factors thought to play key roles are ectoparasitic mites Varroa destructor and neonicotinoid pesticides. The present study aims to investigate effects of a neonicotinoid pesticide Imidacloprid and Varroa mites individually on survivorship, growth, physiology, virus dynamics and immunity of honey bee workers. Our study provides clear evidence that the exposure to sublethal doses of Imidacloprid could exert a significantly negative effect on health and survival of honey bees. We observed a significant reduction in the titer of vitellogenin (Vg), an egg yolk precursor that regulates the honey bees development and behavior and often are linked to energy homeostasis, in bees exposed to Imidacloprid. This result indicates that sublethal exposure to neonicotinoid could lead to increased energy usage in honey bees as detoxification is a energy‐consuming metabolic process and suggests that Vg could be a useful biomarker for measuring levels of energy stress and sublethal effects of pesticides on honey bees. Measurement of the quantitative effects of different levels of Varroa mite infestation on the replication dynamic of Deformed wing virus (DWV), an RNA virus associated with Varroa infestation, and expression level of immune genes yields unique insights into how honey bees respond to stressors under laboratory conditions.     

New experimental data on use of rotenone as an acaricide for control of Varroa destructor in honey bee colonies

Three slow release experimental rotenone formulations were tested to evaluate their effectiveness against Varroa destructor Anderson & Trueman in colonies with sealed brood and to determine whether they left residues in honey and bees wax: we evaluated cardboard strip containing 1 g rotenone and two types of polyvinyl chloride (PVC) strips containing 1 (high-dose) and 0.5 (low-dose) g of rotenone, respectively. In general, the efficacy of the treatments, expressed as percentage of mite mortality, was highly variable in all treatment groups (range, 0-96.8%). The highest effectiveness was obtained with the high-dose-PVC strips, which caused an average percentage of mortality ranging between 47 and 69% in the adult bees and sealed brood, respectively. At the end of the treatment, rotenone residues ranged between 0.03 and 0.06 and 1.5-144.0 mg/kg in honey and wax, respectively. Rotenone residues in wax were still detectable 4 mo after the treatment period, whereas no residues were found in honey. The higher residues content and persistence recorded in wax samples, was probably due to the lipophilic nature of rotenone. A reduction in the amount of adults was recorded for the group treated with high-dose-PVC strips compared with the untreated colonies. Toxicological risks connected with the use of rotenone and the low maximum level recently fixed by European legislation (0.01 mg/kg) suggest that rotenone is not a good candidate for reducing varroa populations in honey bee colonies.     

狄斯瓦螨和蜜蜂残翅病毒对蜜蜂健康的协同影响

世界各地大范围的西方蜜蜂Apis mellifera蜂群损失现象已引起科学界和公众的持续关注。狄斯瓦螨Varroa destructor和蜜蜂残翅病毒(Deformed wing virus,DWV)是西方蜜蜂群中最主要的两大生物威胁。尽管二者侵害蜜蜂均已有较长历史,但直至近十年来的研究才发现两者间的协同效应对蜂群健康的影响远超过其单独作用时所造成的危害:(1)蜜蜂残翅病毒可在狄斯瓦螨体内大量复制,继而进一步传播;(2)狄斯瓦螨的刺吸行为使病毒粒子跨越寄主的生理屏障而直接进入蜜蜂血淋巴;(3)狄斯瓦螨的寄生促使蜜蜂残翅病毒的高毒力毒株在蜂群中优势扩增和盛行;(4)狄斯瓦螨影响蜜蜂个体发育与免疫系统等生理机能,以致降低了蜂群对病毒的抵抗力;(5)蜜蜂残翅病毒对宿主造成的免疫抑制有利于狄斯瓦螨的寄生与繁殖。狄斯瓦螨、蜜蜂残翅病毒和西方蜜蜂间的关系已经成为昆虫外寄生物、病原体与寄主相互作用研究的一个典型模型。本文对近十年该领域的相关研究进行综述,以期为蜂群损失的原因调查以及昆虫寄生虫、病原微生物与寄主间关系的研究提供参考和借鉴。     

Observation of Varroa destructor behavior in capped worker brood of Africanized honey bees

The behavioral activity of Varroa destructor was observed using transparent cells. Mite oviposition started at 45.0?±?25.0?h post capping, followed by the next eggs laid at regular 27.3?±?2.0?h intervals. On the prepupa, mites were found to feed often and there was no preference for a specific segment as a feeding site. During the pupal stage the mite fed less often and almost always at the same point. Varroa showed a preference for defecation in the posterior part of the cell. A significant association was observed between the position of the feeding point in the pupa and the defecation site on the cell wall. Displacement behavior was observed in 71?% of the infested bee larvae and a major change in the free space available for varroa in the cell occurred when the prepupa molted into a pupa.     

Effect of acaricide resistance on reproductive ability of the honey bee mite Varroa destructor

The reproduction of pyrethroid-resistant Varroa destructor mite, a brood parasite of honey bees, was observed in Weslaco, Texas, and the results compared with known susceptible mite populations from other studies. Seven Apis mellifera colonies that had mite populations resistant to the acaricide Apistan^™ were used. Pyrethroid-resistance was confirmed when only 17% rather than 90% of mites confined in dishes containing Apistan^™ died after 12 h of exposure. The average number of eggs laid by resistant mites invading worker and drone cells was 4.4 and 5.4 respectively. This is similar to the number of eggs laid by susceptible mites in worker (4.4–4.8) or drone (4.7–5.5) cells. Also the average number of fertilised V. destructor female mites produced by resistant mites in worker (1.0) and drone (2.1) cells were similar to the number produced by susceptible mites in worker (0.9) and drone (1.9–2.2) cells. In addition, no major differences between the resistant and susceptible mite populations were observed in either worker or drone cells when six different reproductive categories and offspring mortality rates were compared. Therefore, it appears that there is little or no reproductive fitness cost associated with pyrethroid resistance in V. destructor in Texas. This revised version was published online in July 2006 with corrections to the Cover Date.     

Population growth of Varroa destructor (Acari: Varroidae) in commercial honey bee colonies treated with beta plant acids

Varroa (Varroa destuctor Anderson and Trueman) populations in honey bee (Apis mellifera L.) colonies might be kept at low levels by well-timed miticide applications. HopGuard^® (HG) that contains beta plant acids as the active ingredient was used to reduce mite populations. Schedules for applications of the miticide that could maintain low mite levels were tested in hives started from either package bees or splits of larger colonies. The schedules were developed based on defined parameters for efficacy of the miticide and predictions of varroa population growth generated from a mathematical model of honey bee colony–varroa population dynamics. Colonies started from package bees and treated with HG in the package only or with subsequent HG treatments in the summer had 1.2–2.1 mites per 100 bees in August. Untreated controls averaged significantly more mites than treated colonies (3.3 mites per 100 bees). By October, mite populations ranged from 6.3 to 15.0 mites per 100 bees with the lowest mite numbers in colonies treated with HG in August. HG applications in colonies started from splits in April reduced mite populations to 0.12 mites per 100 bees. In September, the treated colonies had significantly fewer mites than the untreated controls. Subsequent HG applications in September that lasted for 3 weeks reduced mite populations to levels in November that were significantly lower than in colonies that were untreated or had an HG treatment that lasted for 1 week. The model accurately predicted colony population growth and varroa levels until the fall when varroa populations measured in colonies established from package bees or splits were much greater than predicted. Possible explanations for the differences between actual and predicted mite populations are discussed.     

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.     

Variability of the honey bee mite Varroa destructor in Serbia, based on mtDNA analysis

Only two mitochondrial haplotypes (Korea and Japan) of Varroa destructor, the ectoparasitic honey bee mite, are known to be capable of infesting and successfully reproducing in Apis mellifera colonies worldwide. Varroa destructor (then called Varroa jacobsoni) was observed in Serbia for the first time in 1976. In order to obtain insight into the genetic variability of the mites parasitizing A. mellifera we analyzed 45 adult female mites sampled from nine localities dispersed throughout Serbia. Four fragments within cox1, atp6, cox3 and cytb mtDNA genes were sequenced. The Korea haplotype of V. destructor was found to be present at all localities, but also two new haplotypes (Serbia 1 and Peshter 1) were revealed, based on cox1 and cytb sequence variability. The simultaneous occurrence of Korea and Serbia 1 haplotypes was observed at five localities, whereas Peshter 1 haplotype was identifed at only one place.     

Reproduction of Varroa destructor in worker brood of Africanized honey bees (Apis mellifera)

Reproduction and population growth of Varroa destructor was studied in ten naturally infested, Africanized honeybee (AHB) (Apis mellifera) colonies in Yucatan, Mexico. Between February 1997 and January 1998 monthly records of the amount of pollen, honey, sealed worker and drone brood were recorded. In addition, mite infestation levels of adult bees and worker brood and the fecundity of the mites reproducing in worker cells were determined. The mean number of sealed worker brood cells (10,070 ± 1,790) remained fairly constant over the experimental period in each colony. However, the presence and amount of sealed drone brood was very variable. One colony had drone brood for 10 months and another for only 1 month. Both the mean infestation level of worker brood (18.1 ± 8.4%) and adult bees (3.5 ± 1.3%) remained fairly constant over the study period and did not increase rapidly as is normally observed in European honey bees. In fact, the estimated mean number of mites fell from 3,500 in February 1997 to 2,380 in January 1998. In May 2000 the mean mite population in the study colonies was still only 1,821 mites. The fertility level of mites in this study was much higher (83–96%) than in AHB in Brazil(25–57%), and similar to that found in EHB (76–94%). Mite fertility remained high throughout the entire study and was not influenced by the amount of pollen, honey or worker brood in the colonies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic bases of tolerance to Varroa destructor in honey bees (Apis mellifera L.)

Currently, the Varroa destructor mite is the most serious parasite of honey bees (Apis mellifera) and has become a nearly cosmopolitan species. The mite not only causes damage by feeding on the haemolymph of honey bees, but it also transmits viruses, which have been implicated in colony collapse disorder. The major research goal has been to breed mite-tolerant honey bee lines in order to reduce the amount of pesticide used, because pesticides can promote the evolution of resistance in mites. In this review, we describe different behavioural traits and genes that may be part of the defence against the Varroa mite. Specifically, we review grooming behaviour, Varroa-sensitive hygiene and the suppression of mite reproduction. A large number of candidate genes have been identified by Quantitative Trait Loci studies, and through gene expression studies their function and effect have been elucidated. Results from the studies discussed can be used in apiary practice.     

Effects of honey bees on colonies of Exoneura asimillima,an Australian native bee

Honey bee hives were placed, during two consecutive summers, in an experimental site which contained natural and artificially placed colonies of Exoneura asimillima, a semi-social, native bee. Two classes of colonies were studied: founders, and established colonies. Nests and contents were collected from an experimental site and three control sites following several months of exposure at the experimental site to the apiary honey bee population. Nest contents were analysed for differences among sites in colony population parameters which could have been caused by resource competition with introduced honey bees. Colony founding and overall colony survival were also considered. During the first season, the average number of large larvae plus prepupae per colony was significantly higher in the experimental site than in the control site. This difference could, however, have been the result of a two-week gap in sampling all the sites. All nest parameters showed high variability and there were no other significant differences between the two kinds of site. In the experimental site during the second season there were, relative to the control sites, significantly fewer total numbers of adult males and females in established nests and in all nests combined, significantly more immatures of all stages in founder nests and significantly lower adult male:female ratio. Although preliminary in nature, the data suggest that, in the experimental plots, E. asimillima showed: (i) increased adult emigration, (ii) increased brood rearing success, and/or (iii) relatively later colony founding, compared to the three controls. The possibility of resource competiton with honey bees causing the observed changes is discussed, along with alternative explanations.     

Efficacy assessment of soft and hard acaricides against Varroa destructor mite infesting honey bee (Apis mellifera) colonies,through sugar roll method

The parasitic mite Varroa destructor is amongst the most serious problems of honey bees, Apis mellifera (Hymenoptera: Apidae) around the world including Pakistan. The present study estimates the mite density through powdered sugar roll method and evaluates the effectiveness of five miticides (fluvalinate, flumethrin, amitraz, formic acid, and oxalic acid) on A. mellifera colonies in German modified beehives. The results indicated that by treating the bees with one strip and two strips of fluvalinate per colony; the mite population remained below the economic threshold level (ETL) for 14 days and 25 days, respectively. Treatment of flumthrin @1 strip and @ 2 strips per colony resulted in mite population suppressed for 14 days and 39 days, respectively below ETL. Application of Amitraz @ 2 mL per 1.5 L water after every three days interval on sealed brood effectively controlled mites below ETL for 21 days. Formic acid @10 mL per colony applied through plastic applicator proved effective (below 3 mites per bee sample) for 24 days and oxalic acid applied through shop towel method resulted in mite population control for fifteen days. Use of powdered sugar roll method for easy sampling of Varroa mites and application of acaricides on precise economic threshold level during different seasons of the year for integrated management of Varroa mite is hereby advocated by current studies.     

Host adaptations reduce the reproductive success of Varroa destructor in two distinct European honey bee populations

Honey bee societies (Apis mellifera), the ectoparasitic mite Varroa destructor, and honey bee viruses that are vectored by the mite, form a complex system of host-parasite interactions. Coevolution by natural selection in this system has been hindered for European honey bee hosts since apicultural practices remove the mite and consequently the selective pressures required for such a process. An increasing mite population means increasing transmission opportunities for viruses that can quickly develop into severe infections, killing a bee colony. Remarkably, a few subpopulations in Europe have survived mite infestation for extended periods of over 10 years without management by beekeepers and offer the possibility to study their natural host-parasite coevolution. Our study shows that two of these "natural" honey bee populations, in Avignon, France and Gotland, Sweden, have in fact evolved resistant traits that reduce the fitness of the mite (measured as the reproductive success), thereby reducing the parasitic load within the colony to evade the development of overt viral infections. Mite reproductive success was reduced by about 30% in both populations. Detailed examinations of mite reproductive parameters suggest these geographically and genetically distinct populations favor different mechanisms of resistance, even though they have experienced similar selection pressures of mite infestation. Compared to unrelated control colonies in the same location, mites in the Avignon population had high levels of infertility while in Gotland there was a higher proportions of mites that delayed initiation of egg-laying. Possible explanations for the observed rapid coevolution are discussed.     

Selection for outbreeding in Varroa parasitising resistant honey bee (Apis mellifera) colonies

Parasitism is expected to select for counter‐adaptations in the host: driving a coevolutionary arms race. However, human interference between honey bees (Apis mellifera) and Varroa mites removes the effect of natural selection and restricts the evolution of host counter‐adaptations. With full‐sibling mating common among Varroa, this can rapidly select for virulent, highly inbred, Varroa populations. We investigated how the evolution of host resistance could affect the infesting population of Varroa mites. We screened a Varroa‐resistant honey bee population near Toulouse, France, for a Varroa resistance trait: the inhibition of Varroa's reproduction in drone pupae. We then genotyped Varroa which had co‐infested a cell using microsatellites. Across all resistant honey bee colonies, Varroa's reproductive success was significantly higher in co‐infested cells but the distribution of Varroa between singly and multiply infested cells was not different from random. While there was a trend for increased reproductive success when Varroa of differing haplotypes co‐infested a cell, this was not significant. This suggests local mate competition, through the presence of another Varroa foundress in a pupal cell, may be enough to help Varroa overcome host resistance traits; with a critical mass of infesting Varroa overwhelming host resistance. However, the fitness trade‐offs associated with preferentially co‐infesting cells may be too high for Varroa to evolve a mechanism to identify already‐infested cells. The increased reproductive success of Varroa when co‐infesting resistant pupal cells may act as a release valve on the selective pressure for the evolution of counter resistance traits: helping to maintain a stable host–parasite relationship.     

Efficacy of strips coated with Metarhizium anisopliae for control of Varroa destructor (Acari: Varroidae) in honey bee colonies in Texas and Florida

Strips coated with conidia of Metarhizium anisopliae (Metschinkoff; Deuteromycetes: Hyphomycetes) to control the parasitic mite, Varroa destructor (Anderson and Trueman) in colonies of honey bees, Apis mellifera (Hymenoptera: Apidae) were compared against the miticide, tau-fluvalinate (Apistan) in field trials in Texas and Florida (USA). Apistan and the fungal treatments resulted in successful control of mite populations in both locations. At the end of the 42-day period of the experiment in Texas, the number of mites per bee was reduced by 69-fold in bee hives treated with Apistan and 25-fold in hives treated with the fungus; however mite infestations increased by 1.3-fold in the control bee hives. Similarly, the number of mites in sealed brood was 13-fold and 3.6-fold higher in the control bee hives than in those treated with Apistan and with the fungus, respectively. Like the miticide Apistan, the fungal treatments provided a significant reduction of mite populations at the end of the experimental period. The data from the broodless colonies treated with the fungus indicated that optimum mite control could be achieved when no brood is being produced, or when brood production is low, such as in the early spring or late fall. In established colonies in Florida, honey bee colony development did not increase under either Apistan or fungal treatments at the end of the experimental period, suggesting that other factors (queen health, food source, food availability) play some major role in the growth of bee colonies. Overall, microbial control of Varroa mites with fungal pathogens could be a useful component of an integrated pest management program for the honey bee industry.