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Funded Project |
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Funding Program:
Regional IPM Competitive Grants - Northeastern |
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Project Title:
Organic Acids as Alternative Controls and Resistance-Management Tools in Parasitic Honey Bee Mite IPM |
Project Directors (PDs):
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Lead State: NJ Lead Organization: Rutgers University |
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Cooperating State(s):
Pennsylvania |
| Research Funding: $54,875 |
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Start Date: Jul-15-2004 End Date: Nov-14-2006 |
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Pests Involved: varroa mites |
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Site/Commodity: honeybees, honey bees |
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Summary:
Honey bees are the only reliable commercial pollinator for over 80 crops in the United States, whose cumulative annual value exceeds $47 billion. Parasitic bee mites are the greatest challenge to beekeepers and a serious threat to bee-pollinated crops. Since the introduction of tracheal and varroa mites, there has been a severe reduction in the managed honey bee population (from 4.5 to 2.7 million colonies).
Tracheal mite control with menthol is highly variable. Chemical overuse for varroa control has resulted in mite populations that are resistant to fluvalinate (Apistan?) and coumaphos (CheckMite+ ?), and pose honey contamination risks. Non-chemical control strategies are considered too laborious by many beekeepers. Mite-resistant bee breeding endeavors show promise, but are not yet fully realized or may be hampered by open-mated (uncontrolled) commercial queen rearing practices. Organic acids (formic and oxalic acid) may offer beekeepers effective, sustainable alternatives for controlling parasitic mites. If successful, these organic acids represent practical, economically viable alternatives for reducing or eliminating the use of conventional pesticides to control parasitic mites of the honey bee. Problem, Justification, and Background Honey bees are the only reliable commercial pollinator for over 80 crops grown in the United States (Delaplane and Mayer 2000; Free 1993; McGregor 1976), with an annual summed value estimated at $47 billion (Morse and Calderone 2000). Of this amount, approximately $14.6 billion are directly attributable to honey bee pollination in terms of increased fruit set and quality. Honey bees also pollinate plants that serve as food resources for wildlife, as well as unknown millions of dollars worth of fruits and vegetables in the home garden. Although less than the value of pollination, the revenue generated by the sale of honey, beeswax, and other hive products is also considerable (ca. $250 million/year). With the number and diversity of crops that require bee pollination in mind, it becomes clear that honey bees are an indispensable aspect of US agriculture. Moreover, the viability of the honey bee industry influences more that just the livelihood of individual beekeepers, but has far-reaching implications throughout society that extend from crop growers to the shipping and packaging industries, through wholesale and retail marketing networks, and so on, eventually reaching the end-user of these commodities, the consumer. Thus, if the honey bee industry were to be compromised, it would have a cascading, negative effect on the US. This is especially true now, as we address the potential threat of bioterrorism in relation to food safety issues. While the US will always import a vast amount of foreign-grown products, it is also essential that we have a sustainable, domestic source of food as much as possible. Honey bee pollination is one of the major keys to the sustainability of US agriculture. Unfortunately, a compromised honey bee industry is exactly what we now have. In the mid-1980's, two honey bee parasitic mites, the tracheal mite (Acarapis woodi) and varroa mite (Varroa destructor), were introduced into the US. In the 18 years since mite establishment and due to their continual nationwide presence, there has been a severe reduction in the number of managed honey bee colonies (from 4.5 to 2.7 million colonies; before and after mite introduction, respectively). Even with control measures in place, beekeepers annually report 40-80% colony mortality (De Jong 1997). Together, these two parasites pose a serious threat to US beekeeping and may have eventual, negative impacts on domestic crop yields, consumer food availability, and food safety. Tracheal mites are endoparasites that infest the breathing systems of adult worker honey bees. The results of heavy infestation are many, and include a reduction in worker bee life expectancy (Maki et al. 1986), injury to the hypopharyngeal (food) glands (Lui et al. 1989), destruction of flight muscle tissue (Komeili and Ambrose 1990), and impairment of thermoregulatory ability (Skinner 2000). Altogether, these stresses drastically reduce the overwintering success of honey bee colonies, particularly in the colder regions of North America (De Jong et al. 1984). Colony mortality is often two or more times greater in northern states than in southern states (Furgala et al. 1988). Varroa mites are ectoparasitic on pupal and adult honey bees. Low infestations result in decreased vitality of individual worker bees through loss of hemolymph (Shimanuki et al. 1992), which may impair the ability of bees to perform hive duties (e.g., brood rearing, comb construction, and nectar collection). High varroa infestations result in the outright death of pupating bees, the malformation (shortened abdomens, misshapen wings, deformed legs) of emerging bees, or a reduced life expectancy of adult bees (De Jong 1997); all of which have negative effects on the viable population and hive dynamics of the honey bee colony (De Jong et al. 1982; Schneider and Drescher 1987). Varroa parasitism is further complicated by the ability of these mites to transmit bee viruses (Ball et al. 1999; Nordstrom et al. 1999), leading to additional stresses on individual bees and the colony as a whole. Without chemical intervention by the beekeeper, honey bee colonies will typically die within 6-18 months of varroa infestation. This fact is supported by the near total loss (> 95%) of feral honey bees which are not actively managed by beekeepers (Ambrose 1997). Varroa mites have spread to all of the beekeeping continents, and can be considered one of the greatest threats to global beekeeping endeavors. Current bee mite control in the United States Effective varroa mite control strategies currently rely on conventional pesticides. For over a decade, US beekeepers have used Apistan® (tau-fluvalinate; Wellmark) to control varroa mites. Varroa infestations occur such that two treatments per year are needed to keep bee colonies alive. Non-rotational use, misuse, and abuse of this product eventually led to the development of varroa strains resistant to fluvalinate (Baxter et al. 1998; Elzen et al. 1998), the occurrence of which is now reported in many states throughout the US. Under emergency use registration (Section 18), another product became available in the 1997, CheckMite+® (coumaphos; Bayer). This product is effective against fluvalinate-resistant mites, but presents a greater user-risk and hive product contamination hazard due to the lipophilic nature of organophosphates. Thus, there is an increased likelihood of pesticide residues in honey and beeswax. Because the safe use of CheckMite+® requires careful attention, many states have registered coumaphos as a restricted-use pesticide that requires the beekeeper to undergo and obtain pesticide application training. Other states have chosen not to register it. CheckMite+® is therefore more difficult to obtain, presents a hazard to user and product, or is simply unavailable to many beekeepers. To exacerbate the problem, reports of varroa resistance to coumaphos have been recently documented, even though this product has only been available for several years (Elzen and Westervelt 2002; Nasr 2002). As a final note to demonstrate the need for alternative varroa treatments, pyrethroid- and organophosphate-based pesticides are both known to contaminate honey and beeswax (deGreef et al. 1994; Gamber 1990; Slabezki et al. 1991; Wallner 1999), which creates additional stress on beekeepers and damages the wholesome reputation of honey. Tracheal mite control is predominantly attempted in the fall with menthol crystals and vegetable shortening patties (Shimanuki et al. 1992). Menthol crystals are positioned above the honey bee brood nest and require consistent temperatures above 21OC (70OF) for several weeks to achieve adequate sublimation of menthol vapors and subsequent mite control. Vegetable shortening patties (e.g., Crisco®) interfere with tracheal mites' ability to detect and attach to new worker bee hosts and/or suffocate the mites by coating their bodies (Delaplane 1992). Due to temperature, colony size, and other factors, the efficacy of either treatment varies considerably by colony and location, and both are typically less effective in northern states than in southern states (Scott-Dupree and Otis 1992; Wilson et al. 2000). Therefore, tracheal mites and winter bee mortality are more problematic for beekeepers in the northern regions of the US. Alternative methods for mite control Several alternatives to conventional pesticides have been developed and show a wide range of efficacy for controlling varroa mites. Physical controls such as screened bottom boards remove varroa mites as they fall off their adult bee hosts in the brood nest. This device is not a stand-alone strategy (14-28% control), and colonies still require eventual chemical intervention (Pettis and Shimauki 1999). Cultural controls such as the trapping of varroa mites in drone brood comb show higher efficacy than modified bottom boards (Grobov 1997; Rosenkranz and Engels 1985; Calis et al. 1998, 1999; Buchler 1997), but the technique is labor intensive, and requires specialized drone comb and freezers to kill mites. Moreover, the removal of infested drone brood from active bee colonies must be timed precisely so that the beekeeper does not accidentally amplify the varroa population by allowing varroa to emerge from drone combs. The essential oil product, ApiLifeVAR®, has shown 70-95% efficacy, but is more expensive than conventional pesticides (three applications are needed), can only be used for fall control, and may negatively affect queen performance (Ellis et al. 2001; Stanghellini unpublished). The breeding of bee stock that is tolerant or resistant to tracheal and varroa mites shows great promise (Danka 2000; Rinderer et al. 2001; Harris and Harbo 2001), and can be considered the ultimate option for controlling these parasites. However, these breeding programs may have to incorporate a second tier of breeding for tolerance to mite-transmitted bee viruses, require large-scale adoption by commercial queen breeders, and will likely be subject to variable queen performance due to open-mated (uncontrolled) commercial queen rearing practices. Much more work is needed on the logistical aspects of specialty queen stock before these genotypes gain the dominant role in nationwide tracheal and varroa mite control practices. Due to variable queen stock and the labor-intensive nature and incomplete control of physical and cultural tactics, most beekeepers must still rely on hard chemicals for varroa mite control. This is especially true for commercial beekeepers, which typically do not have the time or resources to perform these strategies on their 500-50,000 bee colonies. Another, possibly more practical, approach is the use of reduced-risk compounds to control tracheal and varroa mites. Biopesticides may offer beekeepers a safe, practical, yet effective means of parasite control, and are strong candidates for incorporation into an overall parasitic bee mite IPM program. These compounds could reduce or eliminate the need for hard chemicals by keeping mite populations below the established economic thresholds, and can serve as resistance-management tools for treating bee colonies suspected of hosting fluvalinate- and/or coumaphos-resistant varroa mites. Some biopesticides, such as formic acid, have the additional benefit of efficacy against both bee mite species. Most of these biopesticides represent negligible or nonexistent risks to beekeepers and hive product quality and/or safety. European scientists have conducted a considerable amount of research on varroa control with organic acids (formic and oxalic acid) and essential oils (thymol, eucalyptol, and others) (Imdorf et al. 1996, 1999; Fries 1997; Nanetti et al. 2003). While these compounds have proven to be effective alternatives for pyrethroids and organophosphates, their efficacy and timing of application depend on temperature, nectar flow, brood status, and bee and parasite population development. Therefore, it is essential that these alternative control methods be evaluated and adapted to regional environmental conditions and bee management practices. Organic acid use against bee mites Formic acid occurs naturally in honey at levels dependent on the plant species from which bees have collected nectar. Formic acid has been approved for use by beekeepers in the US for the control of both tracheal and varroa mites. However, the only approved method for treating bee colonies with formic acid has been the gel formulation, Apicure® (Feldlaufer et al. 1997). Despite reasonable efficacy against both mite species (ca. 60-80% for both species), Apicure® was removed from the market shortly after its introduction in the late 1990's because of handling and storage safety problems. While the label gave detailed directions for the use of this product, some beekeepers unknowingly exposed too much or too little gel surface area, leading to several problems. Mishandling of open packets sometimes released the gel, resulting in skin irritations and minor burns on the beekeepers' hands, or the gel dripped into the hive and killed bees. Large openings in the gel packet released too much vapor, repelling adult bees and/or killing brood. Small cuts in the packet gave low vaporization rates and did not adequately control mites. No other formulation of formic acid has yet been approved in the US, leaving a gap in the beekeepers' arsenal of known anti-mite products. In Canada, single application formic acid treatments (MiteAway® pads) were developed and are used by many beekeepers in that country (Nasr 1996). As part of a multi-tactic bee mite IPM strategy, these pads are effective against both bee mites and their use is considered safe to beekeepers and bees (Nasr et al. 1996). As a singular, non-IPM approach, MiteAway pads soaked with formic acid were tested in New York for the fall control of varroa, but provided insufficient control (< 60%) (Calderone 1999; Calderone and Nasr 1999). The low efficacy of formic acid was attributed to insufficient formic acid release rates, which are dependent on daily temperatures and the evaporating surface areas of the pads. Calderone (1999) and Calderone and Nasr (1999) concluded that considerable adjustments in the release characteristics of formic acid pads must be made before the device can be used for effective control of varroa mites. Tracheal mites were not addressed in these reports. In late 2003, a preliminary evaluation of a new formic acid release pad (MiteGone®; MiteGone Enterprises Inc., BC, Canada) was conducted in New Jersey for the late fall control of both tracheal and varroa mites (Stanghellini, Appendix I). These pads are different from MiteAway pads in design, composition, placement within the hive, and vapor release characteristics. Efficacy against varroa with MiteGone pads was greater than the levels reported for MiteAway pads (Calderone 1999; Calerdone and Nasr 1999), and averaged 71.9% (ca. 20% increase in efficacy compared to MiteAway pads). Adjusting the application time, duration of treatment, and/or vapor volume might increase the efficacy of formic acid in MiteGone pads above 71.9%. This preliminary test was also designed to evaluate the effects of formic acid on tracheal mites, but these data were still being processed at the time this proposal was written. Alternating a formic acid treatment with a hard chemical would reduce the use of conventional pesticides by 50%, and would serve as a tool to combat mite resistance. Formic acid pads represent a strong candidate for incorporation into a parasitic bee mite IPM program. However, to achieve effective mite control, more work must be done on the optimal conditions, dosage rates, delivery methods, and timing of formic acid treatments in different regions of the US, particularly the northern US where the windows for tracheal and varroa mite treatment are shortened due to overall environmental factors (e.g., cooler fall temperatures). Oxalic acid is a naturally occurring compound in many vegetables, ranging from 0.01 (sweet corn) to 1.70 (parsley) g/100g (USDA 1984). It is also present in some honeys, depending on the floral source of the nectar (Brodsgaard et al. 1999). While the exact mode of action is unknown, various formulations and treatments have been tested in Europe against varroa mites, where some treatments reached greater than 90% efficacy (Thomas 1997; Brodsgaard et al. 1999; Buchler 2000; Nanetti et al. 2003). Like formic acid, oxalic acid is inexpensive compared to conventional miticides, and poses a low to no honey contamination risk (Mutinelli et al. 1997). Scientifically explored methods for applying oxalic acid into beehives have focused on the spray and trickle methods for the late-fall control of varroa (Nanetti et al. 2003). Direct spraying of adult bees with an oxalic acid solution provided effective control of varroa, was well tolerated by the bees, but may be considered too labor-intensive for most beekeepers (Brodsgaard et al. 1999; Thomas 1997). Less invasive and equally effective is the trickling method, whereby variable concentrations of oxalic acid (1.8-4.5%) are dissolved in sugar syrup (0-60% concentrations) and trickled onto adult bees, the volume of solution depending on bee colony size and strength (30-50 ml/colony) (Nanetti et al. 2003). In addition to a wide array of concentrations, the interpretation and applicability of European data to US conditions is complicated by differences in beehive design (e.g., Dadant versus Swiss hives) and brood cycling, which varies by region (e.g., southern versus northern Europe). A Canadian-based company (Heilyser Technology Ltd., Sidney, British Columbia, Canada) also offers an oxalic acid-impregnated plastic strip (Oxamite®) and an oxalic acid fogger device for use against varroa mites. However, there are, as of yet, no published scientific reports on the efficacy of either of these products. Regardless of application method, there are conflicting reports as to the effects of oxalic acid on bees, ranging from no deleterious effect (Nanetti et al. 2003) to impaired queen performance and overwintering success (Hiiges et al. 1999). The effect of oxalic acid on tracheal mites has been largely unexplored, as tracheal mites are less problematic in Europe. Recent studies (Brodsgaard et al. 1999) also indicate that spring treatments with oxalic acid are possible, despite the conflicting reports on its effects on bees and brood. The effects of two oxalic acid applications within the same season have not been explored. In late 2003, a preliminary evaluation of a 3.2% oxalic acid solution applied by the trickling method was conducted in New Jersey for the late fall control of both tracheal and varroa mites (Stanghellini, Appendix I). The efficacy of this oxalic acid treatment against varroa mites averaged 86.9%, and is similar to the results found by European researchers using similar concentrations and methods of application. Adjusting the timing of application, dosage rate, and/or frequency of treatment might increase the efficacy of oxalic acid above 86.9%. This preliminary test was also designed to evaluate the effects of oxalic acid on tracheal mites, but these data were still being processed at the time this proposal was written. The natural occurrence of oxalic acid in honey and vegetables, and its efficacy against varroa mites, make oxalic acid a prime candidate for incorporation into a parasitic bee mite IPM program. However, it is apparent from the European literature and my preliminary trials in New Jersey that more work needs to be done to determine the most efficacious delivery technique, dosage rate, timing of application, and conditions suitable for treatment with oxalic acid. Treatment efficacy and bee safety issues for oxalic acid should be explored in detail under various US conditions before any commercialization of a product is attempted. Stakeholder inputs and needs assessment Beekeepers face numerous challenges including microbial diseases, agricultural pesticide use, and bulk honey importation issues; yet it is the continual battle against mites that creates the greatest hardships. Due to need for parasite control, beekeeping today requires a substantially greater investment of time, labor, and money than in previous decades. Based on a conservative estimate of $7 per colony, it can be calculated that American beekeepers are spending over $18.9 million dollars per year for parasitic bee mite control with conventional pesticides and current recommendations (e.g., fluvalinate and menthol crystals). Not only are the treatments expensive, there are continual problems with conventional pesticide use, including the development of mite populations that are resistant to registered (Apistan; fluvalinate) and Section 18 emergency use (CheckMite+; coumaphos) products, and the risk these products pose to honey and beeswax contamination. A recent survey of 800 New Jersey honey bee colonies was conducted by Nasr (unpublished) to determine the prevalence and impact of parasitic mites on beekeeping practices in this and nearby states (northeastern US). In winter 2001, beekeepers lost more than 50% of their colonies, with tracheal mite infestation as the primary cause. In 2002, an inspection of commercial beekeeping operations (500 colonies or more) found that over 55% of the colonies had tracheal mites, and these colonies were relocated to Florida to increase winter survival rates. If these colonies had remained in New Jersey, all or nearly all of these infested colonies would have been killed. Moving colonies to warmer winter locations is not typically an option for hobbyist (1-50 colonies) and sideliner (50-300 colonies) beekeepers. Therefore, any beekeepers unable to move their hives are expected to lose a considerable proportion each winter, even when subjected to menthol crystal treatments. In 2002, all New Jersey bee colonies had varroa mite infestation levels that required treatment by the fall season. The same or similar trends are likely to be found throughout the northeastern US. Nasr (unpublished) also conducted a questionnaire survey of beekeeper concerns and practices in New Jersey in 2001. Beekeepers were asked to rank bee pests by their impact, and catalog their current and desired parasitic mite management practices. Over 85% of the questionnaires were completed and returned by beekeepers that, collectively, manage approximately 65% of the honey bee colonies in New Jersey. The proportion of completed surveys illustrates the concern beekeepers have about their colonies, bee pests, and their businesses. Beekeeper responses indicated that tracheal mites continue to be one of the most serious problems. Because the monitoring and detection of tracheal mite levels requires a relative degree of technical skill (body dissection), chemical solvents (potassium hydroxide) needed to dissolve flight muscle tissue to view trachea, and access to microscopes, tracheal infestations are often undetected by many beekeepers. Routine treatment with approved controls (menthol crystals) does not always provide adequate control in New Jersey and other northern states. Varroa mites were considered equally destructive as tracheal mites. Beekeepers indicated frustration by the limited number of effective control options. Most of the beekeepers reported that they were "forced" to use CheckMite+ (coumaphos) for varroa control, because of suspected or known fluvalinate-resistance and unavailability of alternative treatments such as formic acid. Beekeepers using coumaphos listed safety to humans, contamination of beeswax, and residues in honey as very strong concerns. Most beekeepers (87%) reported that they would prefer to utilize alternative methods for bee mite control. Organic acids were ranked the number one choice. Development of a safe and effective method to control mites was their number one priority. Respondents indicated that they are willing to adopt new pest management strategies, as long as the tactics are effective, safe, inexpensive, and environmentally sound. The development of organic acid-based alternatives to control mites will require a considerable amount of work. Preliminary and existing studies on organic acid use in beekeeping (cited above) demonstrate that various factors must be taken into account, including environmental conditions, colony status, treatment dosage rates, and timing of application. These factors will likely vary by locality, and so need to be tailored to specific geographical areas, such as the northeastern region of the US. Objectives: (1) define optimum conditions, dosage rates, and timing of applications of formic and oxalic acid treatments to optimize their efficacy in controlling mite infestations in managed honey bee colonies; (2) evaluate the implementation of IPM tactics based on the use of organic acids and a physical control barrier for parasitic mite control; and (3) determine treatment effects on colony health status. USDA CRIS data Final Report Presentation Highlighted in July 2008 IPM Insights |
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