This project tested if there is a relationship between mite-biting behavior MBB levels and the total number of Varroa mites in a honeybee colony. MBB is a recently described grooming behavior trait that has been documented at high levels in some honeybee stocks, but it has yet to be proven as an effective and practical tool for controlling/reducing Varroa mite populations.
The study group encompassed Pennsylvania, Ohio, West Virginia, and Indiana, consisting of 35 honey bee colonies, which we sampled on multiple time points yielding in 127 data points. Analyzing our results we found that 1) Mite biting behavior negatively/inversely correlates to mite drops/populations, and 2) Purdue/MBB genetic parentage positively correlates to MBB percentages. Although, the statistical correlation between the variables in this study is not a particularly strong one, it is significant and encouraging for further investigation of the relationship between genetic background and MBB. Winter survivorship was above the national average, with a mortality rates of: Group 1=13%, Group 2=11%, and Control=14%. Anecdotally, we observed that MBB colonies produced more honey, and overall increased vigor. The 2015 season was marked regionally with substantial Fall losses due to being overwhelmed by mites; the MBB bees stole the remaining honey from collapsing neighboring hives, and also brought back hitchhiker mites with them, and guard bees groomed them off, killed them, and left them in piles next to the entrance. This leads us to conclude, that more work is warranted but with a different experimental design.
Varroa mites are the single greatest threat to sustainable beekeeping in the Northeastern US and across the world. High Varroa mite loads lead to to decreased colony size, strength, health, and are the top factor associated with overwintering losses. Varroa transmits viruses and immunosuppresses bees such that virus titers can rise greatly. Weakened colonies are susceptible to secondary, opportunistic diseases such as foulbrood and Nosema. Currently the majority of commercial beekeepers use treatments of insecticides/miticides for Varroa parasites. These treatment methods have come under scrutiny as to their long-term efficacy because of mites developing resistance, and the side effects on bees, including their ability to rear brood.
This project measured relationship between MBB levels and the total number of Varroa mites in a honeybee colony. MBB is a recently described grooming behavior trait that has been documented at high levels in some honeybee stocks bred at Purdue University by Dr. Greg Hunt. This study evaluated if MBB is an effective and practical tool for controlling/reducing Varroa mite populations. During the 2015 season, we measured MBB percentages in 35 colonies located in: Pennsylvania, West Virginia, Ohio, and Indiana, and performed by members of the Heartland Honey Bee Breeders Coop (HHBBC).
It is important to determine whether MBB can control Varroa mites since selective breeding of honey bees for this trait has potential to increase the sustainability of beekeeping by reducing pesticide and labor inputs, and increasing bee health, honey production, and profitability.
Our objective was to measure the relationship between mite-biting behavior (MBB) and the total mite count in honeybee colonies. We measured the proportion of chewed mites in a colony using the method developed by Dr. Greg Hunt at Purdue University .
We measured MBB rates and the Varroa mite dropsin honeybee colonies. We compared MBB stocks, MBB hybrids generated by artificially inseminated (AI) queens with semen from previously identified MBB stocks, and our best regional survivor stock and a commercially available stock of unselected bees obtained from a Southern breeder. We aim to determine the effect of MBB on Varroa mite loads and provide insights for selective breeding for this genetic trait in our state breeding programs.
The method has two major components, collection of mites, and evaluation of chewed legs. The collection of mites in the field by beekeepers is simple: (1) an oiled board is inserted over the bottom board, allowed to remain for 24-72 hours, then the mites are scraped off of the and onto petri dish; (2) view each mite on the slide under a low power microscope/15X-handlense and count how many mites have chewed/missing legs, then calculate the MBB, as a percentage, example: 12 chewed mite/ 36 total = 33%. Some pictures were taken with a digital microspope that we used to perform this assay, Picture 1 Mite with legs on, and
Picture 2 Mite with legs chewed off with indicator arrows. We compared three groups: 1) HHBBC-bred queens Artificially Inseminated with semen from MBB stocks raised in Purdue 2) queens from best local survivor stock (overwintered) from the HHBBC (3) queens obtained from commercial breeder.
The beeyards locations used are in the HHBBC members respective states: J Berta PA, M Gingrich PA, Dan O’Hanlon WV, D Wells OH, and D Schenefeld IN. Each yard will include 4 colonies from each group.
We measured the project colonies on 3 timepoints. Starting August, and ending in October, approximately 2 weeks apart. Note: some beekeepers started early (PA, WV), other later in the season (OH), and one not at all (IN), which was a deviation from the original research plan.
It was interesting to note that the Purdue MBB bees seemed to produce more honey, than the control bees, although we did not weigh the hives. We had a Penn State graduate student, Mehmet Ali Doke perform the statistical analyses. The following is an excerpt of the results:
” Varroa drop numbers (Figure 1) – Group 2 had the highest daily mite drop numbers (36.12 mites/day), Group 1 was intermediate (28.67 mites/day), and Group 3 had the lowest number (23.17 mites/day). Even though the correlation between genetic background and Varroa counts were not particularly strong (Rsq=0.062), this relationship was statistically significant (p=0.0186). While the genetic background of colonies has an effect on the number of mites dropped, there seems to be other factors affecting this. Here it should be noted that mite drop is not independent from mite infestation which is further correlated with general colony health, population size, demographics and many other individual and colony level factors. Hence, it is an experimental and statistical challenge to explain mite drop by a single factor.
Varroa biting rates (Figure 2) – Group 1 had the highest percentage of chewed Varroa mites (38.68%) within the total that had dropped on sticky boards, Group 2 was intermediate (32.06%), and Group 3 had the lowest percentage (20.91%) (p=0.0074, Rsq=0.087). Similar to what we found for Varroa loads of colonies of different genetic backgrounds, this is a weak but significant correlation indicating contribution from other factors that were not included to the experimental design here and create potential areas for future research on the relationship between MBB and genotype.
Varroa drop numbers vs. biting rate (Figure 3) – Biting rates of colonies in this study were negatively correlated with number of Varroa mites dropped by the colonies (p=0.0035, Rsq=0.066). The significant negative correlation between MBB frequency and Varroa loads of colonies indicates MBB can be effective in controlling mite populations without the use of miticides. The red line in Figure 3 represents the fit of correlation. A larger slope of the fit line (hence the Rsq value) indicates stronger correlation between the variables.” The Mr. Doke’s complete report and charts are attached to this report.
Although the correlation between MBB and mite counts is weak; there are several observations that are important:
1. It seems as the mite population went up, so did MBB. Historically, mite population skyrocket in August through October, and the bees seemed to respond the threat my more biting of mites.
2. We observed piles of dead mite near the entrances of the colonies. Possibly the bees were setting up a ‘battle line’ by grooming field bees as they returned from ‘robbing out’ collapsing hives in the area. The 2015 season was marked regionally with substantial Fall losses due to being overwhelmed by mites; the MBB bees stole the remaining honey from collapsing neighboring hives, and also brought back hitchhiker mites with them, and guard bees groomed them off, killed them, and left them in piles next to the entrance.
3. Control group (Group 3) showed MBB, which diluted the statistical analysis and correlation. Upon further investigation of group 3, there was history of them biting and chewing at times in the past. Finding a proper control with no MBB at all is virtually impossible as this trait is likely observed in all honey bee colonies to a certain extent. This is an important outcome of our study that should be considered during experimental design for future studies.
4. Winter survivorship was better than expected being above the national average. As of February 1, 2016 we had remaining a total of: Group 1 10/12, Group 2 8/9, and Group 3 Control 6/7 of the colonies that we had started with in the fall of 2015. This translates to a mortality rate of: Group 1=13%, Group 2=11%, and Control=14%; the natioanl average hav exceeded 30% for the past several years, (see table of winter survivorship).
We measured MBB percentages in 35 colonies, located in Pennsylvania, Ohio, and West Virginia; Note, Indiana is part of the study but no data could be acquired. We collected 127 samples, and measured MBB percentages. The raw and calculated data entered into an excel spreadsheet, and was statistically analyzed.
The outreach field days received incredible response as we taught backyard beekeepers how to produce queens and nucleus colonies on their own. By distributing winter hardy MBB stock to local beekeepers, we reduced the need for purchasing package bees that are not locally adapted.
NPR did a show about the project which generated international response.
Education & Outreach Activities and Participation Summary
The project had a substantial outreach consisting mostly of spreading the advanced MBB genetics, and informing hobbyist beekeepers how to select and produce their own stock.
June 27, 2015 Queen cell exchange at Slippery Rock, PA attended by queen producers from PA and OH. Master Beekeeper Joe Kovaleski presented advanced queen rearing techniques. MBB genetics were exchanged by 95 queen cell larvae.
July 11, 2015 Queen mating nuc producing feild day in Linesville, PA. Almost 100 queens were mated using MBB genetics using queen cell cups inserted into participants own nuclues colonies which they brought. Over 65 attended.
August 1, 2015 Mated and virgin queen cell exchange at the PA State Beekeepers Picnic. Over 30 queens were exchanged.
NPR did a radio program on the project which involved Penn State advisors Dr. Christina Grozinger and Maryann Frazier, and Jeff Berta. The show aired locally in August, and again nationally in January 2016. Based on this 2016 broadcast we have received inquiries from across the US, Hawaii, and Sweden.
Report and outreach – November 13-14, 2015 PSBA annual meeting in Lewisburg, PA- Queen producers from approximately 35 counties were updated on the 2015 progress.
Pennsylvania Queen Bee Improvement Project Facebook page was updated to include the latest activities with a video about the mite biting assay. Also, posted to the Facebook for Heartland Honey Bee Breeders Coop; we have received several thousand views.
Two major contributions will be long-standing after the conclusion of this project:
1) Improved honeybee genetics – which now have the MBB trait added to our HHBBC “foundation stock” queen bees.
2) HHBBC relationship with local bee clubs and backyard beekeepers. Many of the HHBBC breeders have been contacted and are now an intergral part of their respective honeybee improvement programs. For example, so far at least 3 more field days are being planned for 2016, just in the state of Pennsylvania alone.
This project sets the ground for much more extensive investigation of genetic background of MBB and its use for Varroa control.
We found that MBB is important to the overall health of the hive, and also increases honey production. Also, we found that MBB is not unique to the Purdue breeding program, which is additional genetic treasure. Evaluated by Purdue and incorporated appropriately into the breeding program by Dr. Hunt, these additional lines can aid the already continuing efforts for selective breeding for MBB..
Follow-up studies with improved experimental design will likely yield in larger and cleaner data sets and improve our understanding of the significance of MBB. We have submitted a SARE grant proposal for 2016 for tackling further questions that remain unanswered at this point.
Besides our best efforts to understand this important trait, other research groups’ efforts and collaborations are needed to get a complete picture, and our results should be an encouragement for further studies.