Live Varroa jacobsoni (Mesostigmata: Varroidae) fallen from honey bee (Hymenoptera: Apidae) colonies

The proportion of Varroa jacobsoni Oudemans that were alive and mobile when they fell from honey bees, Apis mellifera L., in hives was measured during a 20-wk period to determine the potential use of systems that prevent these mites from returning to the bees. Traps designed to discriminate between the live, fallen mites and those that are dead or immobile were used on hive bottom boards. A large fraction of the fallen mites was alive when acaricide was not in use and also when fluvalinate or coumaphos treatments were in the hives. The live proportion of mitefall increased during very hot weather. The proportion of mitefall that was alive was higher at the rear and sides of the hive compared with that falling from center frames near the hive entrance. More sclerotized than callow mites were alive when they fell. A screen-covered trap that covers the entire hive bottom board requires a sticky barrier to retain all live mites. This trap or another method that prevents fallen, viable mites from returning to the hive is recommended as a part of an integrated control program. It also may slow the development of acaricide resistance in V. jacobsoni and allow the substitution of less hazardous chemicals for the acaricides currently in use.     

Field evaluation of neem and canola oil for the selective control of the honey bee (Hymenoptera: Apidae) mite parasites Varroa jacobsoni (Acari: Varroidae) and Acarapis woodi (Acari: Tarsonemidae)

Neem oil, neem extract (neem-aza), and canola oil were evaluated for the management of the honey bee mite parasites Varroa jacobsoni (Oudemans) and Acarapis woodi (Rennie) in field experiments. Spraying neem oil on bees was more effective at controlling V. jacobsoni than feeding oil in a sucrose-based matrix (patty), feeding neem-aza in syrup, or spraying canola oil. Neem oil sprays also protected susceptible bees from A. woodi infestation. Only neem oil provided V. jacobsoni control comparable to the known varroacide formic acid, but it was not as effective as the synthetic product Apistan (tau-fluvalinate). Neem oil was effective only when sprayed six times at 4-d intervals and not when applied three times at 8-d intervals. Neem oil spray treatments had no effect on adult honey bee populations, but treatments reduced the amount of sealed brood in colonies by 50% and caused queen loss at higher doses. Taken together, the results suggest that neem and canola oil show some promise for managing honey bee parasitic mites, but the negative effects of treatments to colonies and the lower efficacy against V. jacobsoni compared with synthetic acaricides may limit their usefulness to beekeepers.     

Pseudomonas contamination of a fungus-based biopesticide: Implications for honey bee (Hymenoptera: Apidae) health and Varroa mite (Acari: Varroidae) control

The ectoparasitic mite Varroa destructor is a major honey bee pest, and its control using pathogen-based biopesticides would resolve many of the problems, such as contamination and pesticide resistance, experienced with chemical control. A biopesticide, formulated with commercially-prepared conidia of a strain of Beauveria bassiana isolated from V. destructor was tested against the mites in bee colonies in southern France. The impact of treatment on hive survivorship, weight and mite infestation levels were very different from those of previous experiments using laboratory-prepared conidia: bee hives treated with the biopesticide died at a higher rate, lost more weight, and had higher mite densities at the end of the study than control hives. The biopesticide was subsequently found to be contaminated with bacteria. Two strains of bacteria were identified, by biotyping and sequencing data of the 16S rRNA and rpoB regions, and while the strains were distinct both were Pseudomonas sp. belonging to the P. fluorescens group. In dual cultures B. bassiana growth was slowed or suppressed when bacterial cfu density was about equal or greater than that of B. bassiana. Experiments using caged adult bees showed that bees ingesting diet and sugar solution treated with B. bassiana and kept at 30 °C had significantly lower survival times than those treated with one of the bacterial strains, but the opposite was true at 33 °C. Because one arthropod (honey bees) was treated for infestation by another (V. destructor), the impact of bacterial contamination was likely more noticeable than in most uses of biopesticides, such as treating plants against phytophagous insects. To reduce such risk in biopesticide development, a systematic screening for bacterial contamination prior to field application is recommended.     

Short-term fumigation of honey bee (Hymenoptera: Apidae) colonies with formic and acetic acids for the control of Varroa destructor (Acari: Varroidae)

Controlling populations of varroa mites is crucial for the survival of the beekeeping industry. Many treatments exist, and all are designed to kill mites on adult bees. Because the majority of mites are found under capped brood, most treatments are designed to deliver active ingredients over an extended period to control mites on adult bees, as developing bees and mites emerge. In this study, a 17-h application of 50% formic acid effectively killed mites in capped worker brood and on adult bees without harming queens or uncapped brood. Neither acetic acid nor a combined treatment of formic and acetic acids applied to the West Virginia formic acid fumigator was as effective as formic acid alone in controlling varroa mites. In addition, none of the treatments tested in late summer had an effect on the late-season prevalence of deformed wing virus. The short-term formic acid treatment killed > 60% of varroa mites in capped worker brood; thus, it is a promising tool for beekeepers, especially when such treatments are necessary during the nectar flow.     

Survival of the mite Varroa jacobsoni Oud. (Mesostigmata: Varroidae) in broodless colonies of the honey bee Apis mellifera L. (Hymenoptera: Apidae)

Varroa mite free colonies of the honey bee Apis mellifera L. were artificially infested, with either parasitized bees or infested worker brood. Queens were kept in cages to provide broodless conditions during the experiment. Parasites that fell to the bottom of the hive were monitored at 3–4 days intervals for three months. An acaricide treatment was used to recover mites still alive after this time period. Survivorship at each interval was calculated and life table functions of the phoretic mite cohorts were obtained. Trends in survival of Varroa cohorts showed maximum lifespans ranging from 80 to 100 days. Life expectancy of these phoretic cohorts at the beginning of the experiment ranges between 19 to 41, with a mean of 31 days.     

Laboratory evaluation of some plant essences to control Varroa destructor (Acari: Varroidae)

This research was conducted to evaluate acaricidal effects of some plant essences on Varroa mites and the possibility of their usage for Varroa control. First, live Varroa mites were obtained from adult honeybees with CO₂ in a newly designed apparatus. Thyme, savory, rosemary, marjoram, dillsun and lavender essences at concentrations of 2 and 1g/100g (w/w), caused a mite mortality rate of more than 97% and 95%, respectively. Also spearmint at 2g/100g was able to kill more than 97% of Varroa mites. When sprayed on worker honeybees infected with mites, thyme, savory, spearmint and dillsun essences at 2g/100g (w/w) caused 43–58% Varroa mortality. Toxicity of thyme, savory and spearmint essences for worker honeybees was not significantly different from that of controls (acetone and water), but dillsun essence caused 12% honeybee mortality. These results showed that essences of thyme, savory and spearmint have acaricidal properties that could be used for controlling Varroa in honeybee colonies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation of spring organic treatments against Varroa destructor (Acari: Varroidae) in honey bee Apis mellifera (Hymenoptera: Apidae) colonies in eastern Canada

The objective of this study was to measure the efficacy of two organic acid treatments, formic acid (FA) and oxalic acid (OA) for the spring control of Varroa destructor (Anderson and Trueman) in honey bee (Apis mellifera L.) colonies. Forty-eight varroa-infested colonies were randomly distributed amongst six experimental groups (n = 8 colonies per group): one control group (G1); two groups tested applications of different dosages of a 40 g OA/l sugar solution 1:1 trickled on bees (G2 and G3); three groups tested different applications of FA: 35 ml of 65% FA in an absorbent Dri-Loc^? pad (G4); 35 ml of 65% FA poured directly on the hive bottom board (G5) and MiteAwayII™ (G6). The efficacy of treatments (varroa drop), colony development, honey yield and hive survival were monitored from May until September. Five honey bee queens died during this research, all of which were in the FA treated colonies (G4, G5 and G6). G6 colonies had significantly lower brood build-up during the beekeeping season. Brood populations at the end of summer were significantly higher in G2 colonies. Spring honey yield per colony was significantly lower in G6 and higher in G1. Summer honey flow was significantly lower in G6 and higher in G3 and G5. During the treatment period, there was an increase of mite drop in all the treated colonies. Varroa daily drop at the end of the beekeeping season (September) was significantly higher in G1 and significantly lower in G6. The average number of dead bees found in front of hives during treatment was significantly lower in G1, G2 and G3 versus G4, G5 and G6. Results suggest that varroa control is obtained from all spring treatment options. However, all groups treated with FA showed slower summer hive population build-up resulting in reduced honey flow and weaker hives at the end of summer. FA had an immediate toxic effect on bees that resulted in queen death in five colonies. The OA treatments that were tested have minimal toxic impacts on the honey bee colonies.     

Comparative laboratory toxicity of neem pesticides to honey bees (Hymenoptera: Apidae), their mite parasites Varroa jacobsoni (Acari: Varroidae) and Acarapis woodi (Acari: Tarsonemidae), and brood pathogens Paenibacillus larvae and Ascophaera apis

Laboratory bioassays were conducted to evaluate neem oil and neem extract for the management of key honey bee (Apis mellifera L.) pests. Neem pesticides inhibited the growth of Paenibacillus larvae (Ash, Priest & Collins) in vitro but had no effect on the growth of Ascophaera apis (Olive & Spiltoir). Azadirachtin-rich extract (neem-aza) was 10 times more potent than crude neem oil (neem oil) against P. larvae suggesting that azadirachtin is a main antibiotic component in neem. Neem-aza, however, was ineffective at controlling the honey bee mite parasites Varroa jacobsoni (Ouduemans) and Acarapis woodi (Rennie). Honey bees also were deterred from feeding on sucrose syrup containing > 0.01 mg/ml of neem-aza. However, neem oil applied topically to infested bees in the laboratory proved highly effective against both mite species. Approximately 50-90% V. jacobsoni mortality was observed 48 h after treatment with associated bee mortality lower than 10%. Although topically applied neem oil did not result in direct A. woodi mortality, it offered significant protection of bees from infestation by A. woodi. Other vegetable and petroleum-based oils also offered selective control of honey bee mites, suggesting neem oil has both a physical and a toxicological mode of action. Although oils are not as selective as the V. jacobsoni acaricide tau-fluvalinate, they nonetheless hold promise for the simultaneous management of several honey bee pests.     

Varroa jacobsoni (Acari: Varroidae) is more than one species

Varroa jacobsoni was first described as a natural ectoparasitic mite of the Eastern honeybee (Apis cerana) throughout Asia. It later switched host to the Western honeybee (A. mellifera) and has now become a serious pest of that bee worldwide. The studies reported here on genotypic, phenotypic and reproductive variation among V. jacobsoni infesting A. cerana throughout Asia demonstrate that V. jacobsoni is a complex of at least two different species. In a new classification V. jacobsoni is here redefined as encompassing nine haplotypes (mites with distinct mtDNA CO-I gene sequences) that infest A. cerana in the Malaysia–Indonesia region. Included is a Java haplotype, specimens of which were used to first describe V. jacobsoni at the beginning of this century. A new name, V. destructor n. sp., is given to six haplotypes that infest A. cerana on mainland Asia. Adult females of V. destructor are significantly larger and less spherical in shape than females of V. jacobsoni and they are also reproductively isolated from females of V. jacobsoni. The taxonomic positions of a further three unique haplotypes that infest A. cerana in the Philippines is uncertain and requires further study.Other studies reported here also show that only two of the 18 different haplotypes concealed within the complex of mites infesting A. cerana have become pests of A. mellifera worldwide. Both belong to V. destructor, and they are not V. jacobsoni. The most common is a Korea haplotype, so-called because it was also found parasitizing A. cerana in South Korea. It was identified on A. mellifera in Europe, the Middle East, Africa, Asia, and the Americas. Less common is a Japan/Thailand haplotype, so-called because it was also found parasitizing A. cerana in Japan and Thailand. It was identified on A. mellifera in Japan, Thailand and the Americas.Our results imply that the findings of past research on V. jacobsoni are applicable mostly to V. destructor. Our results will also influence quarantine protocols for bee mites, and may present new strategies for mite control.     

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

Experimental and Applied Acarology - The honey bee ectoparasite Varroa destructor is considered the major threat to apiculture, as untreated colonies of Apis mellifera usually collapse within a few...     

Effects of western honey bee (Hymenoptera: Apidae) colony, cell type, and larval sex on host acquisition by female Varroa destructor (Acari: Varroidae).

Female mites of the genus Varroa reproduce on the immature stages of Apis cerana F. and A. mellifera L. Mites are found more often in drone brood than worker brood, and while evolutionary explanations for this bias are well supported, the proximate mechanisms are not known. In one experiment, we verified that the proportion of hosts with one or more mites (MPV, mite prevalence value) was significantly greater for drones (0.763 +/- 0.043) (lsmean +/- SE) than for workers (0.253 +/- 0.043) in populations of mites and bees in the United States. Similar results were found for the average number of mites per host. In a second experiment, using a cross-fostering technique in which worker and drone larvae were reared in both worker and drone cells, we found that cell type, larval sex, colony and all interactions affected the level of mites on a host. Mite prevalence values were greatest in drone larvae reared in drone cells (0.907 +/- 0.025), followed by drone larvae reared in worker cells (0.751 +/- 0.025), worker larvae reared in worker cells (0.499 +/- 0.025), and worker larvae reared in drone cells (0.383 +/- 0.025). Similar results were found for the average number of mites per host. Our data show that mite levels are affected by environmental factors (cell type), by factors intrinsic to the host (sex), and by interactions between these factors. In addition, colony-to-colony variation is important to the expression of intrinsic and environmental factors.     

The effects of temperature and dose of formic acid on treatment efficacy against Varroa destructor (Acari: Varroidae), a parasite of Apis mellifera (Hymenoptera: Apidae)

In order to decrease the variability of formic acid treatments against the honey bee parasite the varroa mite, Varroa destructor, it is necessary to determine the dose-time combination that best controls mites without harming bees. The concentration × time (CT) product is a valuable tool for studying fumigants and how they might perform under various environmental conditions. This laboratory study is an assessment of the efficacy of formic acid against the varroa mite under a range of formic acid concentrations and temperatures. The objectives are 1) to determine the effect of temperature and dose of formic acid on worker honey bee and varroa mite survival, 2) to determine the CT₅₀ products for both honey bees and varroa mites and 3) to determine the best temperature and dose to optimize selectivity of formic acid treatment for control of varroa mites. Worker honey bees and varroa mites were fumigated at 0, 0.01, 0.02, 0.04, 0.08, and 0.16 mg/L at 5, 15, 25, and 35 °C for 12 d. Mite and bee mortality were assessed at regular intervals. Both mite and bee survival were affected by formic acid dose. Doses of 0.08 and 0.16 mg/L were effective at killing mites at all temperatures tested above 5 °C. There was a significant interaction between temperature, dose, and species for the CT₅₀ product. The difference between the CT₅₀ product of bees and mites was significant at only a few temperature-dose combinations. CT product values showed that at most temperatures the greatest fumigation efficiency occurred at lower doses of formic acid. However, the best fumigation efficiency and selectivity combination for treatments occurred at a dose of 0.16 mg/L when the temperature was 35 °C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Survival of honey bee (Hymenoptera: Apidae) spermatozoa incubated at room temperature from drones exposed to miticides

We conducted research to examine the potential impacts ofcoumaphos, fluvalinate, and Apilife VAR (Thymol) on drone honey bee, Apis mellifera L. (Hymenoptera: Apidae), sperm viability over time. Drones were reared in colonies that had been treated with each miticide by using the dose recommended on the label. Drones from each miticide treatment were collected, and semen samples were pooled. The pooled samples from each treatment were subdivided and analyzed for periods of up to 6 wk. Random samples were taken from each treatment (n = 6 pools) over the 6-wk period. Sperm viability was measured using dual-fluorescent staining techniques. The exposure of drones to coumaphos during development and sexual maturation significantly reduced sperm viability for all 6 wk. Sperm viability significantly decreased from the initial sample to week 1 in control colonies, and a significant decrease in sperm viability was observed from week 5 to week 6 in all treatments and control. The potential impacts of these results on queen performance and failure are discussed.     

Factors influencing host choice of the honey bee parasite Varroa jacobsoni Oud

Reproducing Varroa jacobsoni obtained from brood cells of Apis mellifera L. with 13–16 day old bees (pupae) and Varroa mites kept on adult bees for at least 8 days were simultaneously tested for their choice in three host types. Comparisons were made of attractiveness of Varroa jacobsoni to nurse bees, pollen foragers as to larvae from nearly capped brood cells. Host choices were observed in Petri dishes and in an Y-shaped olfactometer. Varroa jacobsoni obtained from capped brood cells showed a stronger preference for nurse bees in Petri dish simultaneous choice tests with pollen foragers or larvae than did mites which were previously kept on adult bees. In olfactometer simultaneous choice tests, the two mite test groups showed no clear difference in preferences for bees of different ages. The preference of Varroa jacobsoni for bees of different ages is therefore not only influenced by host factors but also by intrinsic factors in female mites that depend on the mite's reproductive stage.     

Complete mitochondrial DNA sequence of the important honey bee pest,Varroa destructor (Acari: Varroidae)

Mites in the genus Varroa are the primary parasites of honey bees on several continents. Genetic analyses based on Varroa mitochondrial DNA have played a central role in establishing Varroa taxonomy and dispersal. Here we present the complete mitochondrial sequence of the important honey bee pest Varroa destructor. This species has a relatively compact mitochondrial genome (15,218 bp). The order of genes encoding proteins is identical to that of most arthropods. Ten of 22 transfer RNAs are in different locations relative to hard ticks, and the 12S ribosomal RNA subunit is inverted and separated from the 16S rRNA by a novel non-coding region, a trait not yet seen in other arthropods. We describe a dispersed set of 45 oligonucleotide primers that can be used to address genetic questions in Varroa. A subset of these primers should be useful for taxonomic and phylogenetic studies in other mites and ticks. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of release mechanisms for botanical oils to control Varroa destructor (Acari: Varroidae) and Acarapis woodi (acari: Tarsonemidae) in colonies of honey bees (Hymenoptera: Apidae)

Two major parasitic pests threaten honey bee populations, the external mite Varroa destructor and the internal mite Acarapis woodi (Rennie). Varroa are beginning to develop resistance to the main chemical defense fluvalinate, and alternative control methods are being pursued. Previous studies have shown that botanical oils, especially thymol, can be effective. Six release devices for either thymol or a blend of botanical oils known as Magic 3 were tested in beehives. The release devices were as follows: (1) low density polyethylene (LDPE) sleeves filled with Magic 3, (2) Magic 3-infused florist blocks, (3) thymol infused florist blocks, (4) a canola oil and thymol mixture wick release, (5) a plastic strip coated with calcium carbonate and Magic 3, and (6) an untreated control. There were significant decreases in varroa levels with the use of Magic 3 sleeves, but brood levels also decreased. Tracheal mite levels significantly decreased with the Magic 3 sleeve treatment, the Magic 3 florist block treatment, and the thymol canola wick treatment. A second experiment showed that changing the location of Magic 3 sleeves in the colony did not detrimentally effect brood levels, but also did not effectively control varroa mites.     

Field trials using the fungal pathogen, Metarhizium anisopliae (Deuteromycetes: Hyphomycetes) to control the ectoparasitic mite, Varroa destructor (Acari: Varroidae) in honey bee, Apis mellifera (Hymenoptera: Apidae) colonies

The potential for Metarhizium anisopliae (Metschinkoff) to control the parasitic mite, Varroa destructor (Anderson and Trueman) in honey bee colonies was evaluated in field trials against the miticide, tau-fluvalinate (Apistan). Peak mortality of V. destructor occurred 3-4 d after the conidia were applied; however, the mites were still infected 42 d posttreatments. Two application methods were tested: dusts and strips coated with the fungal conidia, and both methods resulted in successful control of mite populations. The fungal treatments were as effective as the Apistan, at the end of the 42-d period of the experiment. The data suggested 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. M. anisopliae was harmless to the honey bees (adult bees, or brood) and colony development was not affected. Mite mortality was highly correlated with mycosis in dead mites collected from sticky traps, indicating that the fungus was infecting and killing the mites. Because workers and drones drift between hives, the adult bees were able to spread the fungus between honey bee colonies in the apiary, a situation that could be beneficial to beekeepers.     

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.     

Effective fall treatment of Varroa jacobsoni (Acari: Varroidae) with a new formulation of formic acid in colonies of Apis mellifera (Hymenoptera: Apidae) in the northeastern United States

New formulations of formic acid and thymol, both individually and in combination with various essential oils, were compared with Apistan to determine their efficacy as fall treatments for control of Varroa jacobsoni (Oudemans), a parasitic mite of the honey bee, Apis mellifera L. Percent mite mortality in colonies treated with 300 ml of 65% formic acid averaged 94.2 +/- 1.41% (least square means +/- SE, n = 24), equivalent to those receiving four, 10% strips of Apistan (92.6 +/- 1.79%, n = 6). Treatment with thymol (n = 24) resulted in an average mite mortality of 75.4 +/- 5.79%, significantly less than that attained with Apistan or formic acid. The addition of essential oils did not affect treatment efficacy of either formic acid or thymol. The ratio of the coefficients of variation for percentage mortality for the formic acid (CVFA) and Apistan (CVA) groups was CVFA/CVA = 0.66. This indicates that the formic acid treatment was as consistent as the Apistan treatment. Thymol treatments did not provide as consistent results as Apistan or formic acid. Coefficient variation ratios for percentage mortality for the thymol group (CVT) with the Apistan and formic acid groups were CVT/CVA = 4.47 and CVT/CVFA = 6.76, respectively. In a second experiment, colonies received a 4-wk fall treatment of either 300 ml of 65% formic acid (n = 24) or four, 10% strips of Apistan (n = 6). The next spring, mite levels in the formic acid group (554.3 +/- 150.20 mites) were similar to those in the Apistan treatment group (571.3 +/- 145.05 mites) (P = 0.93). Additionally, the quantities of bees, brood, pollen, and nectar/honey in the two treatment groups were not significantly different (P > or = 0.50 each variable). These results suggest that formic acid is an effective alternative to Apistan as a fall treatment for varroa mites in temperate climates.     

Vitellogenesis in Varroa jacobsoni,a parasite of honey bees

Reproduction in Varroa jacobsoni occurs only in cells of the capped honey bee brood. Female mites were sampled at different times after cell sealing and ovaries containing a vitellogenic oocyte of the first gonocycle were examined under an electron microscope. It was found that the cytoplasmic connection between the lyrate organ and the oocyte persists far into the vitellogenic growth phase. In addition, a large amount of yolk material is taken up from the haemolymph. All ultrastructural features characteristic of vitellogenesis, such as microvilli, coated pits, vesicles and growing yolk platelets, are present. If more than four Varroa females live in an overcrowded brood cell, they appear to be in stress conditions and their vitellogenic oocytes may become atretic. Alterations typical for oocyte degradation and oosorption were observed in such situations.