A honeybee IPM program for pollinator health in blueberry production

Final report for FNE15-833

Project Type: Farmer
Funds awarded in 2015: $15,000.00
Projected End Date: 02/28/2017
Grant Recipients: Fruitwood Orchards Honey; Rutgers University
Region: Northeast
State: New Jersey
Project Leader:
Dennis Wright
Fruitwood Orchards Honey
Dean Polk
Rutgers University
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Project Information


Major NJ beekeepers who pollinate NJ blueberries experienced severe bee mortality in 2014. We experienced up to 40% brood death along with queenless hives that needed to be rebuilt throughout the season. This damage not only contributes to a lack of sustainability for NJ beekeepers, but also contributes to increased pollination costs for NJ blueberry growers, who require about 16,000 hives per year to produce the crop. We established a monitoring system to assess bee mortality, pesticide use, brood health and pesticide residues in hives, as contributing factors in colony decline. Monitored hives were placed on 8 commercial blueberry farms during blueberry pollination. Data was collected by monitoring hive ejected dead bees (1 – 7 day count), percent brood coverage (2 counts), and pesticide residue analyses. Hives were marked for sampling (101 hives). A subset (16) was outfitted with new comb foundation and queens for pesticide residue analyses at the end of pollination. A total of 15 active ingredients were found in pollen and comb samples. Fungicide residues did not correlate with colony decline, but insecticide residues did correlate with decline. Where chlorpyrifos was found, the decline was highly significant. Residues can be minimized by removing bees immediately after pollination to a distance away from commercial blueberry production, and probably by gradually rotating out old comb. One twilight meeting presentation was made to commercial blueberry growers in the spring, and two presentations were made in 2016 winter grower meetings in Atlantic City and Hammonton (total 190 grower and beekeeper contacts).

Project Objectives:

Objectives – 1) Establish an acute bee mortality monitoring system during blueberry pollination. 2) Identify pesticide use during the early part of the season up to bee removal. 3) Correlate hive damage, brood and queen mortality with possible pesticide factors, using a combined pesticide use survey and laboratory screening tests. 4) Create an “off season” communication system with blueberry growers that inform them of beekeeper issues related to pesticide use, and how those issues may relate to blueberry crop yield.


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  • Dean Polk - Technical Advisor (Researcher)


Materials and methods:


During early April of 2015 we constructed 101 trays made of ¼” hardware cloth. These were used to count dead bees removed from the monitored hives as an estimate for field mortality. We also numbered 101 hives to be sampled throughout the pollination season. In front of each numbered hive, we placed a 30″ by 17″ 1/4″ mesh hardware cloth tray used to count dead bees in front of the hive. These 101 numbered hives were placed on 8 farms with a total of 1,548 hives placed on those same farms for pollination. As a subset of the 101 sampled hives, we prepared 16 hives with new wax comb foundations as 50% of the brood box frames (new comb hives), and marked each of these hives. These 16 hives served as the ‘pesticide monitoring hives’ where hives were sampled by digging out pollen/nectar/wax samples from both established and new comb. Hives were placed in commercial blueberry fields starting on April 26, 2015. New comb hives were placed at the rate of 2 hives per site on 8 sites. Field kill estimates were taken with dead bee counts in the hardware cloth trays on May 8-9 when trays were cleaned, and again on May 15-16 for a 7-day count. Brood coverage was measured on both sides of 3 numbered frames: center, second from right, and second from left approximately 7 days after placement (5/7), and again 3 weeks later (5/29) just prior to hive removal from the fields. Both dead bee counts and brood coverage measurements were done on the 101 numbered and marked sample hives. Brood coverage included open cells with live brood or eggs, and capped brood. Hives were noted as queened or queenless. Including the 2 assessments, 1,212 frame surfaces were evaluated during the pollination period. Shortly after hive removal from the fields (24-72 hr.), pollen and comb samples (5-6 gram) were taken from the subset of new comb hives. Pollen samples were placed in glass vials and immediately frozen before being sent to a lab for pesticide residue analyses. Pollen samples were submitted to the National Science Laboratories in Gastonia, N.C. on September 3 and screened for pesticide residues of 174 active ingredients in ppb; method identified as MET-123. A presentation was made to commercial blueberry growers as the project started on April 23. Additional presentations were made to commercial blueberry growers at the New Jersey Agricultural Convention on February 10, and the New Jersey Beekeepers Association on February 13, 2016.

Research results and discussion:


The 7 day dead bee count averaged 27.7 bees per hive and ranged from 0 to 114 dead bees per hive. Most hives had between 10 to 30 dead bees per hive. Since commercial beekeepers do not consider less than 100 dead bees per week a significant number, this data was difficult to interpret as anything significant, especially since it did not measure field kill that may have happened far from the hive.The percent brood coverage was averaged for all 6 comb counts per date, and sampled hives compared by date. The reading on the first date (5/7) was used as the base. Therefore hives should show an increase in brood coverage by the second date (5/29). By 5/29 59 hives out of 101 (58.4%) showed an increase in brood coverage. There was “0” growth or less coverage in 42 hives (41.6%) (Figure 1)2016Figure 1. The goal for the beekeeper was to see at least 30% increase in brood strength during the pollination period. This is represented by the dark horizontal line in Figure 1.  Over 90% of the hives did not make this goal.In the subset of 16 new comb hives 12 of the 16 showed growth and 4 showed “0” growth or shrinkage. Hives rated as queenless were hives where the queen had died and/or a new queen had not been produced. Where farm sites had at least 7 monitored hives, the percent queenless hives at the beginning vs. the end of pollination were compared (Figure 2)2016Figure2. In most cases the number of queenless hives significantly increased throughout the pollination period.

Analyses for pesticide residues showed up to 15 active ingredients were present in sampled hives 2016Table (Table 1). Some of these such as DMPF (a metabolite of Amitraz), Coumaphos and Fluvalinate were common and are attributable to the products used for varroa mite control. Fungicide residues included Azoxystrobin, Fenbuconazole, Metalaxyl, Boscalid, Pyraclostrobin, Captan and the Captan metabolite, THPI. All of these are normally used in blueberries, including just before and during pollination. Other insecticide residues included Esfenvalerate, Imidacloprid, Phosmet, and Chlorpyrifos. Atrazine was found in 3 hives.

This data did show that a significant number of hives showed no growth in brood, and even decreased in strength. This was partly do to an increased level in queen mortality and lack of queen replacement. While low numbers of varroa mites were present in most hives, along with some disease, many pesticide residues were also found. Fluvalinate and coumaphos have known toxic properties to bees, and were formerly used as varroa miticides. Regression analyses were performed on various pesticides vs. percent brood change. This was a small data set with no clean controls and multiple factors influencing survival and mortality. None of the fungicides as related in his data showed a significant correlation with lack of brood growth (Figure 3)2016Figure 3 The R2 value was only .014 with P=.67. Generally the higher the R2 value is to 1 then the stronger the correlation, but the significance of the probability (P) needs to be .05 or less. In other words with a P value of .05 we would be 95% sure that the correlation is significant. Insecticide residues did show a correlation with negative brood growth (Figure 4)2016Figure 4(R2 = .36, P=.019). Individual insecticides that are known be highly toxic to bees likely contributed more to this effect than others. For example none of the other insecticide contaminants resulted with a significant correlation and low P, except Clorpyrifos – Lorsban (P=.05). 

Discussion and Impacts

Two pesticide residues, Chlorpyrifos and Atrazine are not labeled in blueberries and could have been used on other crops within the foraging range of the bees. This area-wide issue of pesticide use and honey bee management needs to be further explored. Bees cannot be expected to stay on the contracted farm and only being influenced by the management by one grower, unless the farm is isolated and surrounded by non-sprayed wild hosts. Since the grower did not use Chlorpyrifos and Atrazine, the residues had to be from a neighboring farm, which likely grew field corn.

Phosmet (Imidan) was found in most of the samples. This is an insecticide that was commonly used immediately after the bees are removed in the first post-bloom insecticide application. A common practice among beekeepers is to remove the hives at the end of blueberry pollination to holding yards that are large enough to gather hives from many locations, before loading them on larger trucks to either isolated holding yards prior to cranberry pollination, or going out of state for additional pollination services. The problem is that these first holding yards are often open gravel pits within 100 yds of active blueberry fields. Therefore when the grower applies post bloom insecticides, the bees are still foraging or passing through the active crop and contacting spray residue. Therefore when blueberry pollination services are done, the hives need to be removed several miles away from the active fields. 

The fact that fluvalinate, as well as trace amounts of coumaphos were found in every ‘new hive,’ and had not been used by the beekeeper for many years, indicates that at least 2 foreign residues are present in beeswax foundation and comb. This finding agrees with other recent hive residue work, and helps support the idea of rotating out old comb on a regular basis in order to minimize pesticide residues.

Many fungicide residues were also present, and are directly attributable to the use in blueberries for anthracnose and botrytis disease control during bloom, and again shortly after bloom. Both the known literature and this data do not point to these residues as being a contributing cause of the observed colony decline, queen death and lack of growth. However, the fact that multiple residues were present, some not even used by blueberry growers, combined with other hive stressors like varroa mites and disease, indicates the highly stressed conditions of the hives. Additionally, new work is showing that certain pesticides can exhibit different toxicological properties on brood as compared to adults alone. Some combined compounds have been shown to synergize toxic properties within the hive. These factors and others point to the need for further work in more controlled conditions.

Research conclusions:


We validated the fact that colonies are declining while in blueberry pollination. We found that bees are contacting and bringing back to the hive, numerous pesticides. Most of these can be traced to actual grower use in the crop, with all of them that were used in blueberries, used properly. Some residues, particularly Phosmet and Captan were used immediately post bloom. Here, the avoidance of these residues falls to the beekeeper to move hives away to sufficient distance after pollination is done. The fact that some pesticide residues are years old in the hive, supports the recommendation to regularly rotate out the oldest comb in favor of new foundation. The finding of Chlorpyrifos and Atrazine in 3 hives suggests that we need a better system of communication among beekeepers and all farmers within the bee forage radius during times of pollination. The bee safety practices that are observed by only those growers who contract for honey bees may not be sufficient if in the end, bees are contacting toxic materials on neighboring farms. This work was presented at several twilight and annual grower meetings.

Participation Summary

Education & Outreach Activities and Participation Summary

18 Consultations
1 On-farm demonstrations
3 Webinars / talks / presentations

Participation Summary

9 Farmers
251 Number of agricultural educator or service providers reached through education and outreach activities

Learning Outcomes

73 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

pesticides and bee safety

Project Outcomes

43 Farmers changed or adopted a practice
1 Grant applied for that built upon this project
1 Grant received that built upon this project
$39,802.00 Dollar amount of grant received that built upon this project
5 New working collaborations
Project outcomes:

Removal of hives immediately post pollination is now done to holding yards totally away from commercial blueberry farms. Recommended that beekeepers annually rotate out a portion of old comb and regularly replace a percentage with new comb foundation in order to minimize pesticide residues. 

The number of farmers who changed practices is based on communication with 43 Cooperative Extension IPM Program participants, recommendations and collection of pesticide use records. This resulted during the following season, that none of these growers used bee toxic insecticides during bloom, and dropped one of the pre-bloom materials known to have detrimental effects on honey bee larvae.  

Assessment of Project Approach and Areas of Further Study:

Blueberry growers need more information on the effects of pesticides on bees, and beekeepers need more information on the potential interactions of varroa mites with diseases and pesticides. We also need more information on the effects of some pesticides thought to be relatively safe, but now suspected of causing negative impacts on honey bee brood. 

We did answer the questions that we originally set out to address. We quantified honey bee mortality and brood growth in the presence of pollination services. We found commonly used pesticides in our hives, some from varroa mite treatments, and others from use in blueberry production.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.