6 Other Funding Approvals Category
6.1 BMG15
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Programme Title: |
Varroa Mite sustainable control |
Programme Leader: |
Bruce Bycroft |
Institution: |
Crop & Food CRI |
Summary
Varroa mite (Varroa destructor) is a major pest of the European honey bee and is found almost worldwide. Without some form of control strategy, varroa can result in managed hives being severely weakened or killed and feral colonies being largely eliminated.
Varroa was first discovered in New Zealand in April 2000. New Zealand beekeepers have benefited from the development overseas of chemical Varroa control methods, including synthetic pyrethroids and organic acids. Application methods vary in their efficacy, probably depending on the distribution of the active ingredient in the beehive.
Background
The Ministry of Agriculture and Forestry provided funding to test the application of Envirosol® technology for the control of varroa mites in beehives. Envirosol® technology is used in horticultural applications such as greenhouses for the control of pests and diseases. The active ingredient is dissolved in liquid carbon dioxide and delivered as a very fine aerosol, enabling pesticides to be distributed evenly in enclosed spaces.
There results indicate that two of the active ingredients evaluated were as effective for the control of varroa mite as Apistan strips in broodless hives, with little or no effect on adult bees.
They will continue to refine the methodology for using Envirosol® technology as an innovative delivery system for the control of varroa.
Introduction
Varroa mite (Varroa destructor) is a major pest of the European honey bee and is found almost worldwide. Without some form of control strategy, varroa can result in managed hives being severely weakened or killed and feral colonies being largely eliminated.
Varroa was first discovered in New Zealand in the Auckland region in April 2000. Since then, it has spread throughout the North Island north of a Movement Control Line gazetted by the Ministry of Agriculture and Forestry (MAF). It has also spread to areas south of that line, including Upper Hutt and the Manawatu and Horowhenua regions.
New Zealand beekeepers have benefited from the development of chemical varroa control methods overseas, including synthetic pyrethroids and organic acids. The current application methods include impregnated polymer strips, proprietary and home-made absorbent pads, crystals and syringes. The success of each application method varies and is likely to be related to its ability to distribute the active ingredient in the hive. Often, direct contact with the active ingredient is required and this occurs mostly through the movement of bees within the hive.
Envirosol® technology was developed by BOC Ltd for the efficient application of pesticides in greenhouses. The active ingredient is dissolved in high pressure liquid carbon dioxide and delivered as a fine aerosol, which can remain suspended in a closed environment for more than 30 minutes. The technology provides even distribution of active ingredients, which can lead to lower pesticide residues and reduced dose rates compared to conventional application methods. They considered that this technology would be an efficient method of applying miticides for the control of varroa.
Funding received from MAF to undertake initial trials to assess the suitability of this technology for varroa control. This report describes the trials and subsequent recommendations.
Approach & Outcomes
Project objectives
The project consisted of three objectives:
- Objective 1: The effect of carbon dioxide on honeybees
Carbon dioxide is occasionally used to anaesthetise bees for operations such as adding queens to export packages. We needed to understand the tolerance of honeybees to carbon dioxide for Envirosol® technology to be considered as a viable option for varroa control.
- Objective 2: The effect of selected Envirosol® experimental formulations on honeybees.
Three active ingredients were tested, each formulated as an Envirosol® and using a range of dose rates, on samples of bees not infested with varroa. Two of the active ingredients tested (AI 1 and AI 2) are currently used for the control of varroa either in New Zealand or overseas but have not previously been formulated as Envirosols. The third active ingredient (AI 3) has been previously formulated as an Envirosol for the control of grain pests but has not been used for the control of varroa in honeybees.
- Objective 3: The effect of Envirosols on varroa mite populations in beehives
Once Objectives 1 and 2 were completed, they tested the efficacy of the selected active ingredients, formulated as Envirosols, on varroa mites and adult bees in infested nucleus beehives north of the Movement Control Line.
Publications
References
- M Goodwin and C Van Eaton (2001). Control of varroa - a guide for New Zealand beekeepers. Ministry of Agriculture and Forestry publication.
- Anon. (2001). Optimal usage of mite control products. Report supplied by MAF on research conducted in 2001.
- Anon. (2002). Code of practice for own use of compounds. MAF Food Assurance Authority.
- R Ryan, N Grant and H Krishna. The Envirosol technology.
- I Floris, P Cabras, V L Garau, E V Minelli, A Satta and J Troullier. Persistence and effectiveness of pyrethroids in plastic strips against Varroa jacobsoni (Acari:Varroidae) and mite resistance in a Mediterranean area. Journal of Economic Entomology, Vol 94, no. 4, pp 806-810.
6.2 var505
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Programme Title: |
Integrated Varroa control (02/03 Programme) |
Programme Leader: |
Mark Goodwin |
Institution: |
HortResearch CRI |
Summary
M.A. Taylor, R.M. Goodwin, H.M. McBrydie and H.M. Cox November 2003
This research programme consists of five projects aimed at developing Integrated Control Programmes for the management of varroa (Varroa destructor) in New Zealand honey bee (Apis mellifera) colonies. These projects are outlined below:
Background
Project 1: Treatment Thresholds
Varroa population thresholds affecting beehive economic performance in two New Zealand climatic/colony development zones were assessed. This is the second year data has been collected for this project. Hives treated in November collected more honey than those treated in January. At present we still suggest that treatment should be conducted when there are more than 40 mites per 300 bees.
Project 2: Breeding varroa tolerant honey bees in New Zealand
This project aims to establish a commercial strain of honey bee that displays a high incidence of the "Delayed Suppression of Mite Reproduction" (SMRD) trait. Due to unsuitable weather conditions and the infertility of the artificially inseminated queens no data could be collected from this project.
Project 3: Alternative Treatments
The effect of different application methods of formic acid and oxalic acid on the control of varroa in New Zealand was assessed. The proportion of varroa killed in single-super hives treated with formic acid was higher than if they were in 2-super hives. Ventilation did not have any significant effect on treatment efficacy. Multiple applications of oxalic acid in the spring or autumn did not result in any significant differences between the amount of brood or bees in the colonies. Up to three applications of oxalic acid was not detrimental to the colonies. Multiple oxalic acid treatments in the autumn did not have a detrimental effect on queen survival. Hives treated with oxalic acid were able to be fed nine litres of sugar syrup simultaneously without having any effect on the efficacy of the oxalic acid treatment.
Project 4: Resistance to Chemical Controls
The aim is to determine base levels of resistance to common chemical control compounds in New Zealand populations of Varroa destructor. The results suggest that varroa are not resistant to any of the chemicals tested. However, it does not appear to be too many seasons before resistance may develop towards fluvalinate as the amounts tested in New Zealand are similar to what varroa have shown resistance to overseas.
Project 5: Testing Model IPM Programmes
Efficacy of different varroa control IPM programmes in New Zealand conditions were assessed. With the current development of the organic treatments available it does not appear that varroa can be controlled in the acute phase without using synthetic treatments.
Approach & Outcomes
This research programme consisted of five projects. These were thresholds, selecting varroa tolerant bees, alternative varroa control methods, chemical resistance and model integrated pest management programmes. The threshold, tolerant bee and IPM trials were part of longer term projects.
Project 1: Varroa Treatment Thresholds
The aim of this research was to determine at what varroa population level beekeepers should treat their hives to avoid economic damage during the acute (invasion) and chronic stages of varroa infestation. Data was collected for this trial for two consecutive seasons from 120 honey bee colonies located in a warm zone (South Auckland) and 120 colonies located in a cold zone (South Waikato). Both seasons' data are included in this report.
All colonies were balanced to four frames of brood at the start of each season and requeened by late November. Supers of drawn foundation were weighed and added to each hive when required. Each month varroa levels were monitored using the sugar shake method in the first season and the Apistan® shake method (Goodwin et al., 2002) in the second. Twenty hives from the first season and 24 from the second were selected each month from each climatic zone and placed on mite collectors for 25 days and treated with Bayvarol®. These treated hives represented the range of varroa levels present each month. The accumulated debris from the treated hives was collected and sub samples were analysed to identify the total mite level in each hive.
Strength (frames of bees and brood) of the 240 colonies was assessed at the beginning of the trial (November), midway through the trial (January), and at the end of the trial. Bee and brood assessments were also conducted on colonies immediately prior to being treated. The hives were wintered down at the end of April and reassessed in spring.
For the first season honey was not collected at the cold sites due to wet weather, which limited foraging. These hives were fed sugar syrup throughout the trial and were therefore not included in the analysis. The amount of honey collected at the warm sites appeared to be more if the hives had been treated early (November) in the season rather than later (January). The economic threshold for the warm site appeared to be less than 100 mites per 300 bees as hives above this value were more likely to die. However, there was not enough data to identify the economic threshold level below 100 mites.
Data from the second season suggested that hives treated early (November) in the season rather than later (January) produced more honey. Combined analysis of both seasons and both zones showed there was a significant difference in honey collection for those hives treated early in the season. The economic threshold appeared to be about 80 mites per 300 bees but again there was not enough data to state whether this level should be lower. We still suggest that treatment should be carried out when mite levels are above 40 mites per 300 bees and that spring treatment should be conducted before the honey is collected.
Project 2: Breeding Varroa Tolerant Honey Bees in New Zealand
Tolerance (sometimes called "resistance") to varroa is the ability of a honey bee colony to co-exist with an infestation of varroa.
In 2002 sufficient levels of varroa tolerance (10-19% of female mites that do not produce offspring) were found in New Zealand honey bee stocks (Goodwin et al., 2002). This gave reason to establish a breeding programme focused on selecting the SMRD trait in strains of New Zealand honey bees. The aim of this project was to increase the level of varroa tolerance that is known to exist in New Zealand stocks.
Twelve of the 100 nucleus colonies that were assessed during the 2001 - 2002 season had levels above 10% non-reproducing mites. These were selected to begin the programme to breed varroa tolerant bees in New Zealand. The programme was based on the delayed suppression of mite reproduction (SMRD) and used single-drone inseminations to select for this trait.
Grafts were taken from all 12 breeder queens to establish daughter queens that headed five, four-frame nucleus colonies per breeder (Total of 60 hives). These daughter queens were artificially inseminated with semen from either one or two drones produced by its mother. Despite breeding and inseminating over 250 queens, within three weeks of insemination a large proportion of these queens became drone layers and superseded. Data was collected from only one queen and this showed no increase in the SMRD trait.
There are two main reasons why this season's research was not successful. The first is that the erratic spring weather prevented early raising of daughter queens which set the programme back 2 months. Once the daughter queens were raised despite them being inseminated and accepted back into the hives the semen had not migrated to the spermatheca which resulted in the queens laying drone cells. By the time this was established the season was over and the hives had started to shut down brood rearing.
Project 3: Alternative Treatments
Formic acid pouches
The aim of this investigation was to determine if colony size (single and two-super hives) influences the effectiveness of formic acid.
Forty colonies were established in four apiary sites at Ruakura Research Centre, Hamilton. Twenty colonies were in single-super hives and 20 colonies were in 2-super hives.
Formic acid in plastic pouches was applied for 28 days to ten single-super colonies and ten 2-super colonies that had reduced entrances and plastic hive mats (restricted hives). The same treatment was applied to ten single-super colonies and ten 2-super colonies that did not have reduced entrances or hive mats (ventilated hives). Mite mortality was measured using sticky boards. Once the formic acid pouches were removed, new sticky boards and Bayvarol®strips were inserted according to label instructions to determine the remaining mite population not killed by the application of the organic compound.
The data was analysed using GenStat. The estimated proportion of dead varroa was higher in single-super hives than 2-super hives (P-value = 0.003). Hives with restricted ventilation did not have significantly more dead varroa than those that were not (P value = 0.622).
Oxalic acid
The aim of this investigation was to determine the affects of feeding multiple applications of oxalic acid in spring and autumn on queen survival and colony status. The four treatment regimes assessed were applying oxalic acid 0, 1, 2, or 3 times at weekly intervals in spring and then again in autumn.
Sixty-eight colonies were established at four apiary sites at Ruakura Research Centre, Hamilton. Colony strength was assessed by estimating the number of frames of bees and brood. The post-treatment assessments were carried out one week after the final applications of oxalic acid. An increase in brood and bee numbers was expected during this time due to season. Multiple applications of oxalic acid in the spring or autumn did not result in any significant differences between the amount of brood or bees in the colonies. Up to three applications of oxalic acid were not detrimental to the colonies. Multiple oxalic acid treatments in the autumn did not have a detrimental effect on queen survival.
A final trial was conducted in late autumn to assess whether sugar syrup could be fed to colonies at the same time oxalic acid is applied and what impact this may have on the efficacy of the treatment. Feeding nine litres of sugar syrup at the same time as applying the oxalic acid treatment had no effect on the efficacy of the oxalic acid treatment.
Project 4: Resistance to Chemical Controls
The aim of this trial was to establish a base level of resistance to four synthetic chemicals that are or in the future may be used in New Zealand to control varroa. This can then be used to monitor any further development of resistance.
Resistance was measured by placing mites on wax impregnated with the chemicals being tested. The LC50 for flumethrin (10.4 ppm) is within the range expected for `non resistant' varroa. The LC50 for mites surveyed in Italy that had not demonstrated resistance in the field using the same methods were between 0.36 and 20.4 ppm.
The LC50 for fluvalinate was 270 ppm. The LC50 for two sites with resistant mites in Italy was between 385 and 857 ppm. Whether an LC50 of 225ppm would show up as resistance in the field is unknown. Also, because this is the first time this test has been carried out in New Zealand it is not known whether this level of resistance was present with the varroa when they arrived in New Zealand or whether it has since developed. It does however appear that the level of resistance does not have to develop much further before field resistance is observed.
Project 5: Testing Model IPM Programmes
This is the second year of a two-year programme. The trial used the 240 honey bee colonies from the previous season. During the spring mite assessments it was noted that a number of hives were unable to be used, which confounded our results. A second commercial beekeeper supplied additional hives for the autumn part of the project.
Spring treatment
One hundred and twenty hives were situated on five apiary sites in the Waikato (warm climatic zone) and another 120 hives were on five apiary sites in Taupo (cold zone). Three treatment types a) Synthetic = Bayvarol® strips in spring and autumn; b) Combination = Bayvarol® strips in autumn and formic acid plastic pouches in spring; c) Organic = formic acid plastic pouches in spring and oxalic acid in autumn, were randomly allocated between the hives at each site.
The varroa levels in the 240 colonies were assessed using the Apistan® shake method (Goodwin et al., 2002) and the allocated treatments were applied early October 2002. After four weeks the formic acid plastic pouches were removed. After six weeks the Bayvarol® strips were removed and then the mite levels were assessed for all 240 hives.
Prior to the spring treatment the varroa levels at both climatic zones were low, with the majority of hives containing on average 3 mites per Apistan® shake. After the spring treatments were completed the Apistan® shake assessments suggested the varroa levels had increased for the colonies in the combination and organic treatment groups (0-32 = cold zone, 0-86 = warm zone).
Autumn treatment
One hundred and twenty hives were situated on eight apiary sites in the Waikato (warm climatic zone) and another 120 hives were on seven apiary sites in Taupo (cold zone). The colonies were assessed using the Apistan® shake method at the end of February. The mite levels in the colonies at the cold sites and at four of the warm sites were between 0 and 10 mites. The other four warm sites had between 0 and 53 mites so were treated with either formic acid plastic pouches or Bayvarol® strips depending on what treatment they had been allocated. A second synthetic treatment was applied to all hives treated in the autumn with an organic treatment as the post assessments revealed that the mite levels were still above the threshold level of ten mites per 300 bees that had been set.
With the current development of the organic treatments available it does not appear that varroa can be controlled in the acute phase without using synthetic treatments.
For further information please contact: Michelle Taylor, HortResearch, Private Bag 3123, Hamilton, Phone (07) 858 4650, Fax (07) 858 4701
Publications
Taylor, M.A.; Goodwin, R.M.; McBrydie, H.M.; Cox, H.M. 2003. Development of Integrated Control Programmes for Varroa Control in New Zealand 2002-2003. 2nd Edition. A Report to the Ministry of Agriculture and Forestry New Zealand. HortResearch Client Report No. 9725. HortResearch Contract No. 17810.
Contact for Enquiries
Farm Monitoring Programme Manager
Monitoring and Evaluation
MAF Policy
PO Box 2526
Wellington
NEW ZEALAND
Phone: +64 4 894 0623
Fax: +64 4 894 0741
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