Sustainable control of varroa
Taylor MA, Goodwin RM, McBrydie HM, Martinez OD, Evans LJ.
July 2009
A report prepared for National Beekeepers Association Project MAF SFF 07/0800
This work was supported by the MAF Sustainable Farming Fund, The Honey Industry Trust, Zespri, Comvita, cash and in-kind contributions from individual beekeepers and the NBA.
Organic Control of Varroa
2007–2008 Trial
The aim of this trial was to assess the efficacy of four commercially available thymol products for varroa control in honey bee colonies. Honey production from these colonies was also assessed to determine if organic controls had any impact on honey collection.
Ten co-operating beekeepers established a total of 20 hives. Each hive was allocated either a synthetic treatment (Apistan® or Bayvarol®), or one of four organic products (Apilife VAR®, Thymovar®, Apiguard®, and thymol crystals). Each product was applied to both single and double brood box hives.
After the spring 2007 treatment, none of the control hives (those treated with Bayvarol® or Apistan®) had mites in the post-treatment sugar shake test. On average, hives in the organic treatments had 1 to 3 mites in a post-treatment sugar shake. There was a significant difference in the effectiveness of the organic treatments dependent on brood box size (P<0.007) for Apilife VAR® and thymol treated hives.
Apiguard® and thymol treated hives collected significantly less honey (P< 0.05) than control hives.
In autumn 2008, mite numbers increased rapidly. In those hives treated with organic control products, there was still an increase in mite numbers over the treatment period. Initial results indicate that treatment with organic products in mid to late autumn was not effective at controlling varroa.
2008-2009 Season
To determine if the efficacy of Apiguard® could be increased, three variables were assessed:
Oxalic acid, ventilated floor boards and food grade mineral oil (FGMO). Apiguard® was selected from the four organic products based on the “average” opinion provided by the beekeepers after the 2007-2008 season. Their opinions took into account hive loss and therefore effectiveness in mite kill, ease of use, consistency of product, label instructions and swarming.
This season, eight beekeepers each managed 21 double-super colonies. Of the 21 colonies, nine had ventilated floor boards and the remaining 12 had full wooden floorboards.
Three colonies were randomly allocated the following treatments. The first three treatments had one replicate of three colonies with ventilated floors and one with solid floorboards. The last treatment was only applied to colonies with solid floorboards: 1) Bayvarol® /Apistan® 2)Apiguard® 3) Apiguard + oxalic acid 4) Apiguard + oxalic + FGMO.
Varroa levels
The varroa levels from all of the treatment groups pre and post spring treatment and pre autumn treatment were all less than 5 mites per 300 bees. Based on the thresholds of “20” and “40 mites” that were used in this trial the data suggests that a spring Apiguard® treatment controlled varroa as effectively as Bayvarol® over summer, providing the autumn treatment was conducted before the first week of February. In the post autumn treatment assessment the Apiguard® colonies had significantly more mites than the colonies treated with Bayvarol® but of the colonies that were treated by the first week in February only 14.4% required a second treatment and only an additional 7.7% of the colonies required a synthetic treatment. In comparison, 100% of the colonies that were treated 2 weeks later had >100 mites per sugar shake.
Although Apiguard® colonies had significantly higher varroa levels after the autumn treatment than the Bayvarol® colonies it should be noted that the average levels were not above the “40-mite” threshold. This suggests that an additional organic treatment may have been sufficient to effectively control the varroa. All of the 2007/2008 colonies that were treated with an organic product required a synthetic treatment compared with only 7.7% of the colonies this year. This suggests that by treating the colonies at the end of summer it may be possible to control varroa in autumn using two treatments of Apiguard®. As we did not continue looking at the colonies after April we are unable to conclude what happened to the colonies in each of the treatment groups after this time.
Honey production
Honey was removed from the colonies by the first week in February and the allocated treatments were applied no later than this date. The type of treatment or floorboard did not have any effect on the amount of honey collected by the colonies.
Colony size
The type of treatment or floorboard did not have any effect on the size of the colonies.
Selecting Honey Bees that are Resistant to Varroa
Crosses were continued at Ruakura to maintain the gains that were made the previous season. Colonies were also moved to Great Mercury Island to attempt to produce a selfsustaining population of varroa resistant bees. All drones were removed from the colonies before introduction. Queen cells from the resistant stock at Ruakura were then placed in these colonies. Breeder colonies with lots of drones were also placed on the island.
The hives were assessed for resistance in autumn 2008. Only 2 hives were determined to be resistant to varroa. One colony was able to survive without treatment for 13 months and the second colony was able to survive without treatment for 23 months. Colonies were produced from these 2 lines and are being maintained at Ruakura until spring 2009.
The reasons why the other colonies were not resistant was unclear but it appears that the majority of queens that are produced from a breeder line and then naturally mate with other breeder lines do not have a high enough level of resistance to control varroa. In the absence of gene technology the best way to determine if a colony is resistant is by an SMRD % assessment, especially for those colonies that have SMRD levels that do not fully control varroa. From these identified colonies, queen cells can be produced.
For further information, please contact:
Michelle Taylor
The New Zealand Institute for Plant & Food Research Ltd
Plant & Food Research Ruakura
Private Bag 3123,
Waikato Mail Centre
Hamilton 3240
NEW ZEALAND
Tel: +64-7-959 4430
Fax: +64-7-959 4431
Email: mtaylor@hortresearch.co.nz