The honey bee, Apis mellifera, is the major crop pollinator worldwide and a key component in the production of over 90 fruit and vegetable crops in the US, including apples, blueberries and cranberries, which are prominent in agriculture in the northeastern US. The introduction of the parasitic mite, Varroa destructor, to the USA in 1987 poses a major threat to beekeepers and to a sustainable supply of affordable managed colonies required for pollination. We identified a natural product and a non-chemical method for controlling this mite.
The honey bee, Apis mellifera, is an indispensable contributor to the northeastern states’ agricultural and economic environment. Three major crops – apples, blueberries, and cranberries – depend almost entirely on the honey bee for commercial yields. The annual value of these crops exceeds $1 billion, with the northeast accounting for 1/3 of this production. A large number of other crops grown in the region also depend on or benefit significantly from honey bee pollination, including buckwheat, cherries, currants, peaches, pears, plums, raspberries, blackberries, strawberries, melons, squash, pumpkins and cucumbers. Pollination is provided by over 10,000 northeastern beekeepers, including several hundred commercial beekeepers who derive a major portion of their income from beekeeping. Reliable and affordable pollination is critical to both farm productivity and the stability of farm incomes and food prices. Control has been intermittent, and during the1995/96 winter, northeastern beekeepers experienced their largest losses in history, with state losses from varroa ranging from 30-80% of colonies. High losses also occurred during the winter of 2002/2003, as resistance to Apistan, the current varroa control method, continued to become widespread throughout the US. In addition, varroa has reduced the number of feral colonies that have provided a background level of pollination previously taken for granted. We evaluated a number of alternative control methods for maintaining mite populations below the economic injury level. We will seek to integrate these methods into a comprehensive IPM program for varroa control. These projects will provide beekeepers with methods for affordably managing mites without the use of synthetic pesticides, and may allow them to reduce the frequency of applications of natural acaricides. This, in turn, will enable beekeepers to offer high quality hive products, including honey, wax and pollen, in the market place. It will also ensure a sustainable supply of healthy and affordable colonies required for pollination of crops in the northeast.
- Evaluate imported stocks of Russian honey bees and stocks of SMR queens developed by ARS-USDA that are partially resistant to V. destructor;
Optimize the use of formic acid, a natural acaricide, for control of the parasitic mite V. destructor;
Evaluate drone combs as a trap crop for reducing V. destructor levels.
Evaluate screen bottom boards as a method for reducing V. destructor levels.
The projects involved a combination of institutional-based research and beekeeper-facilitated research. The drone-trap method and the screen bottom boards were evaluated at Dyce Lab in Ithaca, NY with the assistance of my apiary technician. The formic acid projects and the evaluation of mite-resistant stocks
The most significant milestone is our demonstration that formic acid, when properly formulated, can be nearly as effective in controlling parasitic mites as either Apistan (fluvalinate) or CheckMite+ (coumaphos), the two conventional pesticides currently registered for this purpose.
Beekeepers often lose colonies during the late summer and early fall due to rapidly expanding mite populations. Unfortunately, this is a time when chemical treatments are not allowed because of label restrictions intended to guard against pesticide residues in the hive.
A second significant milestone is our preliminary finding that drone comb traps can be an effective component in a beekeeper’s mite management program because they help keep the mite population low during the summer, thereby enabling colonies to be healthy in the fall when the treatment window opens. Hopefully, this finding will be supported by the analysis of the last season’s data.
Beekeepers have been hearing a great deal about a number of methods for control of parasitic mites in their beehives. One of the most prominently promoted methods is the screen bottom board. The theory is simple. Mites are known to fall off of adult bees in the hive. Normally, these mites would simply acquire a new host and continue their life-cycle. The screen bottom board allows these mites to fall right out of the colony and therefore, renders them incapable of acquiring a new host. The result is that the mite population either declines or grows less rapidly. Our findings on the efficacy of the highly popular screen bottom board method have revealed no effect on mite populations or honey production whatsoever.
A second method beekeepers have heard about is the drone comb trap method. Adult mites seek the immature stage of the honey bee as a host for reproducing. They may be found in either a worker cell (female) or a drone cell (male). However, adult mites are found in immature drone cells about 10x as often as they are in immature worker cells. This bias reflects the fact that mites using a drone for a host produce about 2x as many offspring as mites using a worker host. By using whole combs of drone comb, large numbers of mites can be collected and removed from the colony. The drone comb with mites is frozen and returned to the colony for another round of drone trapping. In the first year of our drone trap study, we found that worker bee populations were about 2x as great in colonies being treated with drone traps as in colonies in which the drone combs were left in place throughout the season. The second year of the project was aborted due to large winter losses. We completed the third year of the project in 2003 and are currently analyzing the large volume of data collected. We are very encouraged by the results obtained so far, and look forward to continuing to evaluate this method in the future.
Our experience with the mite-resistant stocks of bees currently available has been disappointing. The Russian stock did not prove to be resistant and the SMR stock developed by ARS-USDA produced queens of inferior quality. This was indicated by a high percentage of rejections of these queens by colonies into which we were trying to introduce them. We experienced the same problems with the SMR queens in each of the four operations in which we evaluate them.
We have met with beekeepers during the past three years for the purpose of providing education on sustainable methods for managing parasitic mites. We made the following presentations which dealt either all or in part with sustainable methods for managing parasitic mite populations:
1. IPM: Safe and effective use of pesticides in the beehive.
a. Finger Lakes Beekeepers Association. April 13, 2003, Ithaca, NY
b. Southern Adirondack Beekeepers Association. Albany, NY March 22, 2003
c. Mid-York Beekeepers Association. Oriskany, NY April 8, 2003
d. Empire State Honey Producers Association. Nov. 7, 2003, Alexandria Bay, NY
2. IPM: An Introduction to Reducing Pesticide Use in the Bee Yard. June 22, 2001. MAREC Intermediate Short Course. West Waverly, MD (97 people in attendance)
3. Strategies to Keeping Colonies Healthy. November 10, 2001 Pennsylvania State beekeepers Association. Lewisburg, PA. (55 people in attendance)
4. The Wintering Hive. December 1, 2001. Empire State Honey Producers. Saratoga Springs, NY. (60 people in attendance)
5. Pollination and the Great Insect Plant Relationship. June 26, 2001. 4H focus on Teens Program. CU Plantations, Cornell University. (12 people in attendance)
6. Managing colonies for Pollination. Long Island Agricultural Forum 2000, Riverhead, January 13, 2000. (28 people in attendance)
7. Master Beekeeper Program Update. Empire State Honey Producers Fall Meeting. Owego,NY. November 13, 2000. (60 people in attendance).
8. Effective fall treatment of Varroa destructor with a new formulation of formic acid. Empire State Honey Producers Fall Meeting. Owego,NY. November 13, 2000. (60 people in attendance).
9. IPM. Reducing pesticides in the bee yard.
a. Southeast beekeepers group, Middletown. Jan. 25, 2000 (25 people in attendance)
b. Fingerlakes beekeepers, Ithaca. Jan. 23, 2000. (16 people in attendance)
c. Chemung beekeepers, Horseheads. Jan. 24, 2000. (15 people in attendance)
d. Allegany beekeepers, Allegany county. Jan. 25, 2000 (10 people in attendance)
e. Chautaugua Beekeepers Association. Feb 3, 2000 (15 people in attendance)
f. Southern Tier Beekeepers Association. Feb. 8, 2000 (23 people in attendance)
g. Steuben County Honeybee Association. Feb. 21, 2000 (16 people in attendance)
h. Catskill Mountain Beekeepers. March 3, 2000 (32 people in attendance)
i. Sullivan County Beekeepers Association. March 10, 1999 (22 people in attendance)
j. Western New York Honey Producers. March 12, 2000 (31 people in attendance)
k. Long Island Beekeepers Association. March 18, 2000 (36 people in attendance)
l. Southern Adirondack Beekeepers Association. March 19, 2000 (30 people in attendance)
MASTER BEEKEEEPER WORKSHOPS:
1) Integrated Pest Management: Reducing Pesticide Use in the Bee Yard (1 day)
a. Ithaca, NY, Tompkins County, September 16, 2001. CCE of Tompkins County (6 participants)
b. Greenwich, NY, Washington County, September 29, 2001. BetterBee Inc. (15 participants)
2) Field Day in the bee yard (1 day)
a. Greenwich, NY, Washington County, September 23, 2001. BetterBee Inc. (19 participants)
b. Greenwich, NY, Washington County, September 30, 2001. BetterBee Inc. (20 participants)
c. Ithaca, NY, Tompkins County, September 9, 2001. (20 participants)
d. Ithaca, NY, Tompkins County, September 15, 2001. (16 participants)
3) Apprentice Level – Spring Course 2001 (2 days)
a. Ithaca, NY, Tompkins County, June 10 & 11, 2001 CCE of Tompkins County (20 participants)
b. Greenwich, NY, Washington County, May 6 & 7, 2001. BetterBee Inc. (19 participants)
c. Ithaca, NY, Tompkins County, June 10 & 11, 2001. CCE of Tompkins County (16 participants)
4) Apprentice Level – Fall Course 2001 (1 day)
a. Ithaca, NY, Tompkins County, September 8, 2001. CCE of Tompkins County (15 participants)
b. Greenwich, NY, Washington County, September 22, 2001. BetterBee Inc. (17 participants)
At the conclusion of our data analysis cycle, I will prepare the following publication based on work with formic acid, screen bottom boards and the drone comb trap method:
Calderone, N. W. Evaluation of chemical, cultural and mechanical methods for managing the parasitic mite Varroa destructor in colonies of the honey bee, Apis mellifera.
Impacts of Results/Outcomes
Objective 1: Mite resistant bees:
1. Evaluation of RUSSIAN stock: Using a cooperator’s bees, we compared colonies headed by queens reared from inbred RUSSIAN stock that were allowed to mate naturally with unselected drones. We established a population of 96 colonies, half resistant and half unselected. All queens were reared in a common apiary and allowed to mate naturally with unselected drones. In the fall, we evaluated the mite/bee ratios, but found no significant difference between treatment groups (0.008 ± 0.008 M/B in colonies with unselected stock compared to 0.012 ± 0.004 M/B in colonies headed by RUSSIAN queens. The cooperator reported that colonies headed by RUSSIAN queens were prone to swarming, a highly undesirable trait.
2.Evaluation of SMR stock: We attempted several evaluations of the SMR stock from USDA-ARS. We reared virgin queens from inbred SMR breeder queens and from an unselected stock of bees. In one case, we provided a cooperator with 60 virgins of each type. His job was to introduce them to small colonies and evaluate them over the summer. He reported that 59/60 SMR queens were rejected or disappeared within a few weeks of introduction. With the unselected stock, 59/60 were accepted and performed very well (we did not collect data because there was no SMR treatment group for comparison). Since all queens were reared in the same queen-raring colony and handling thereafter was identical, we assume that the level of inbreeding in the SMR virgins (since they come from inbred SMR stock, all virgins produced from this stock are still inbred – the workers they produce using semen from unrelated and unselected drone sources are F1 hybrids). In a second trial, we provided a cooperating beekeeper with 90 queens, which were introduced with about 50% success. However, shortly thereafter, the beekeeper passed away quite unexpectedly (he was only 51 and in the peak of health), therefore, we were not able to collect data on those hives.
We had somewhat better success in introducing SMR queens in our own colonies at Dyce Lab. Of 90 virgins introduced during the fall (45 SMR and 45 CONTROLS), we retained about half of the SMR queens the following spring. In August, we took ether roll samples from the colonies. CONTROL colonies had an ether roll count of 10.79 ± 1.58 mites, compared to 11.83 ± 1.64 mites in SMR colonies (P > 0.50).
3.Mite breeding program: due to the poor performance of the Russian stock and the SMR stock, we established our own breeding population at Cornell. This population consists of 120 queens from a wide variety of sources. We will be evaluating these for mite resistance, wintering success, honey production and temper during the next several years. Top performers will be used as breeding stock for subsequent generations.
Objective 2: Formic Acid:
1. New bottle formulation of formic acid: We evaluated a new formulation of formic acid. The existing product has a problem with the packaging. The acid dissolves the packaging, rendering the product dangerous to handle. The new formulation makes use of a heavy duty plastic bottle to eliminate this problem. We evaluated this product in two apiaries, each with approximately 24 colonies. We found that the new product provided 86.33 ± 3.21 % control, compared to 55.77 ± 3.21 % mite mortality in control colonies (P < 0.0001). The level of control achieved with this product was a bit lower than previous studies, but was still within the range considered useful. The lower efficacy was probably was due to the low rate of evaporation (39.16 ± 0.04% in one apiary and 37.78 ± 0.04 % in the other apiary). This low rate appears to be due to the dimensions of the product which result in a low evaporative surface-area to volume ratio. 2.Effect of screen bottom boards on efficacy of formic acid treatment for mite control: There is considerable interest among beekeepers in a device known as a screen bottom board. This device replaces the traditional solid bottom board on which the hive rests. The theory is that many mites fall off of mites and land on the bottom board. If it is solid, they can return to the bees, but if it is screened, they fall through and out of the hive. However, there is concern that the open bottom on the screen bottom boards may reduce the efficacy of formic acid because it is heavier than air and may simply flow out of the hive before having an effect on the mite population. We tested our own proven formulation of formic acid on 24 colonies, 12 with traditional bottoms and 12 with screen bottoms. We obtained 86.50 ± 3.1 % mite mortality in hives with screen bottoms and 87.58 ± 3.1 % in hives with traditional bottoms (P > 0.50). Again, these results are probably due to the fact that the evaporation rate of formic acid was relatively low during this unusually cold period (48.13 ± 1.9 % in colonies with solid bottoms and 54.33 ± 1.9 % in colonies with screen bottoms), but still within the acceptable range. These results also provide a good estimation of the effectiveness of formic acid in cold weather. Previous fall applications had been conducted when the weather was much warmer. This past fall, October was unusually cold. The efficacy of the formic acid was reduced, but still sufficient for a fall treatment.
3. Evaluation of two doses of formic acid for control of Varroa destructor: Based on our previous work showing that formic acid could be an effective fall treatment for parasitic mites when applied at 300 ml 65% formic acid per treatment, we decided to evaluate a lower dose to determine the lowest effective dose. We already knew from other studies that 165 ml of 65% formic acid was not effective. Therefore, we compared 250 ml and 300 ml of 65% formic acid with the standard treatment with Apistan. We found that all three treatments yielded similar, satisfactory results. Treatment with 250 ml 65% formic acid gave mite mortality of 95.00 % + 1.8441; 300 ml 65% formic acid gave 95.78 % + 1.8513 mite mortality; and 4, 10% strips of Apistan gave 93.99 % + 1.7989 mite mortality.
Objective 3: Drone comb ‘Trap Crop’:
Mites reproduce in brood cells of honey bees and prefer drone brood to worker brood by a factor of 5 or 10 to 1. Drone foundation makes it possible to produce solid combs of drone cells. These drone combs can be placed in colonies; and after they are full of capped drone brood and mites, they can be removed, frozen to kill the mites, and then returned to the colony for cleaning and another round of treatment.
Trial 1: In our first study, we have measured the size of the colony (Combs of Bees) as an indicator of the effectiveness of this method in managing mites. In colonies with 3 drone comb treatments during the summer, we estimated a cluster size of 6.85 ± 0.94 Combs of Bees, compared to 2.36 ± 0.89 % Combs in colonies without drone comb treatment (P < 0.002). This suggests that this method is highly effective in protecting colonies during the critical time of the season, the late summer, when honey production is still in full swing, but when the colonies cannot be treated with pesticides.
Trial 2: this past year, we repeated our evaluation of the drone comb method. We measured a number of variables, including mite levels on adult bees, honey production, fall cluster size (worker population), total fall mite population, and the amount of drone brood actually removed from each colony. These data are still being analyzed.
Objective 4: Screen bottom boards:
We have evaluated screen bottom boards to determine their effect on mite levels, honey production and wintering success.
1. Trial 1: During the summer of 2001, we conducted our first evaluation of the screen bottom boards. We found that the screen bottom had no significant effect on fall cluster size (9.26 ± 0.55 Combs of Bees for the colonies with the solid bottom board and 8.46 ± 0.54 Combs of Bees in the colonies with the screen bottom boards (P > 0.50). Similarly, we found no significant effect of screen bottom boards on honey production (69.07 ± 5.45 kg in colonies with regular bottom boards and 63.34 ± 5.28 kg in colonies with the screen bottom boards (P > 0.50)). Finally, we did not detect a significant difference in mite levels (mite/bee ratio) between the two treatment groups (0.087 ± 0.018 M/B in colonies with the solid bottoms and 0.11 ± 0.018 M/B in colonies with the screen bottom board (P > 0.50)). A M/B ratio of 0.10 is considered very high.
Trial 2: During the summer of 2002, we continued our evaluation of the screen bottom boards. We found that the screen bottom had no significant effect on fall cluster size (6.38 ± 0.77 Combs of Bees for the colonies with the solid bottom board and 5.73 ± 0.74 Combs of Bees in the colonies with the screen bottom boards (P > 0.50). Similarly, we found no significant effect of screen bottom boards on honey production (39.08 ± 5.59 kg in colonies with regular bottom boards and 36.83 ± 5.59 kg in colonies with the screen bottom boards (P > 0.50)). Finally, we did not detect a significant difference in mite levels (mite/bee ratio) between the two treatment groups (0.036 ± 0.008 M/B in colonies with the solid bottoms and 0.021 ± 0.008 M/B in colonies with the screen bottom board (P > 0.25)).
Trial 3: We had planned to test the screen bottom boards on wintered colonies; however, due to high winter losses, we were forced to repeat our studies with package bees. This proved worthwhile, as the packages had high initial mite levels, which resulted in excellent test conditions for the screen bottom boards. We measured a number of variables, including mite levels on adult bees, honey production, fall cluster size (worker population), total fall mite population, and the amount of drone brood actually removed from each colony. These data are still being analyzed.
The formic acid product for which we are seeking a Section 18 emergency use designation in New York will retail for about the same price as current treatment methods: Apistan and CheckMite+. Beekeepers must build or purchase one additional piece of equipment to use the formic acid product. This is a one-inch wooden rim that fits on the top of the hive and which provides room required for the pad. The cost of the rim is less than a dollar apiece if built by the beekeeper and they are reusable indefinitely.
The drone comb trap requires additional work by the beekeeper. Frames must be built and wired to accommodate the drone comb foundation which the bees then draw out into full-sized drone combs. We recommend two drone combs per colony. Since these combs replace existing worker combs, there is no additional materials cost for the drone comb traps, only the initial labor investment, which is about 5 minutes per comb. There is a need to visit colonies every 30 days to remove drone combs that have been filled and replace them with empty combs or the previous round of frozen drone combs. However, such routine visits are part of most beekeeper’s management strategies anyway, so this does not add significantly to the beekeepers workload.
The results of our research on formic acid have been incorporated into new miticides called Mite-Away II. This is a formic acid product for which we are currently seeking a Section 18, emergency use designation. Until this is approved by US-EPA, US beekeepers are not able to legally obtain this product. Interest in formic acid is high among beekeepers, and we anticipate widespread acceptance of the product throughout the northern regions of the US. Once the product is granted Section 18 status, we will expand our outreach and monitor sales.
Areas needing additional study
The evaluation of stocks of bees that are purported to be resistant or partially resistant to mites has proven disappointing. Either resistance was not significant or the quality of the queens from these stocks was poor. We have established our own breeding program for mite resistance which uses techniques that differ substantially from those used in other programs. We will be selecting for mite resistance, but will require any selected colonies to also be good honey producers (the gold standard) and good winterers in the harsh northeastern climate. We will also use natural mating in isolated mating yards to allow us to produce high quality queens with more vigorous offspring.
We are also planning on using our results on formic acid and the drone trap method to establish several demonstration apiaries that rely solely on these methods for management of parasitic mites. Beekeepers are welcome to visit these sites. We also use these sites for our Master Beekeeper Program, Journey Level, Field Day in the Bee Yard Workshop. This is a very popular workshop that enables beekeepers to work with large numbers of colonies and thereby to greatly increase their understanding of basic bee and mite management.