6. OTHER FUNDING APPROVALS CATEGORY
6.1 VAR 007
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Programme Title: |
Development of Integrated Control Programmes for Varroa destructor Control in New Zealand |
Programme Leader: |
Dr R M Goodwin |
Institution: |
HortResearch |
Summary
This research programme consisted of 6 projects. These were thresholds, sampling, organic treatments, selecting varroa tolerant bees, optimal usage of synthetic treatments, and testing model integrated control programmes.
The threshold for varroa treatments were investigated in hives in cold and warm locations. No thresholds could be calculated for the cold locations as the colonies did not collect a surplus crop. The economic threshold established from the warm location appears to be less than 100 mites per 300 bees. However, despite knowing that 100 mites per 300 bees results in death we do not have enough data to identify at what level below 100 mites the economic threshold occurs. As these results are from one zone, and from one of three seasons, they should be treated with caution. At present we suggest that treatment should be conducted above 40 mites per 300 bees.
The efficacy of the more promising techniques for estimating varroa numbers were investigated as well as the relationship between the number of mites found in a sample of bees and the total number of mites in a hive.
The relationship between the number of mites in a sample of bees, as determined through a sugar shake, and in a hive was determined. The allowance that must be made for varroa in brood cells is termed the brood multiplier. The international brood multiplier is a factor of 6 when the hive is in full production and 2 at other times. The brood multiplier from warm sites fits what has been suggested. The brood multiplier at the cold site did not follow this pattern however. It started very low (<2) in October and climbed steadily till it reached a peak (6) in February.
The amount of icing sugar added to 300 bees in a Mason jar affected the proportion of mites removed from the bees. The best recovery rate was with 10 g of icing sugar. The length of time the icing sugar was left in the jar did not affect recovery rates in any recognisable way. The recovery rate after one sugar shake was only 78%. There was also quite a large variance between samples (S.E. = 4.49). However, when the procedure was repeated on the same bees the recovery rate increased to 95% with a low variance (S.E. = 1.1).
Using an Apistan® strip in a Mason jar with 300 bees was much slower than the other methods but the variance was less. Leaving the jar of bees to stand for 10 minutes resulted in a 42% recovery rate, 20 minutes a 81.6% recovery rate, and 30 minutes a 93.8% recovery rate (S.E. = 1.2).
For the alcohol wash method, the longer the bees were shaken in the alcohol the higher the extraction rate. A maximum varroa recovery rate of 97% was achieved after 4 minutes shaking. However, shaking for only 30 seconds and rinsing the bees two additional times also gave better results (98.3%) and was faster. Washing samples in water containing a low sud detergent produced similar recovery rates to alcohol. Shaking samples for 15 seconds and rinsing the contents of the jar 2 further times with water removed 98.7% of mites.
Puffing fluvalinate, tobacco or grapefruit leaf smoke into a jar full of bees resulted in the recovery of a large number of mites in some cases but very poor recovery rates at other times indicating that the methods are not reliable and should not be used. The recovery rates of the ether roll method were low and the variance between samples high. This method should also be avoided.
The efficacy of seven organic varroa control methods was assessed. The methods were: mite wipes, absorbent pads, plastic pouches, formic acid applied to floorboards, thymol sprinkled on the top bars of frames, thymol in dishes on the top bars and oxalic acid. Both the formic acid and oxalic acid treatments killed significantly more varroa at the cold site in both the 2001 and 2002 trials. There was a high level of corrosion on galvanised iron lid and hive components after the formic acid treatments.
Formic acid in mite wipes, absorbent pads and plastic pouches, as well as thymol, all gave similar levels of control at the cold sites (>77%). However, formic acid applied to floorboards gave a lesser level of control (58%). Oxalic acid gave lower control levels, probably because of the amount of brood in the hives (59%). Thymol was the best of the treatments tested giving high levels of control at both cold and warm sites (>80%).
A trial was conducted to assess the level of tolerance to varroa present in New Zealand bee stocks. Queen bees were purchased from each of 8 queen producers in the North and South Islands. These were tested for tolerance to varroa by estimating the number of varroa infesting honeybee pupae that didn’t produce offspring. The percentage of mites not reproducing varied between 0 and 19%. The best of these have been kept for inclusion in the breeding programme.
The efficacy of Apistan® and Bayvarol® treatments was investigated. When used at the entrance of a hive Apistan® was as effective as when it was placed inside hives. However, Bayvarol® was less effective at killing mites when used at the entrance. In all other treatments the two products were equal. Using them at half the recommended rate was as effective as using them at the recommended rate. Freezing the strips did not affect their efficacy.
Three varroa control programmes were tested on commercial hives in warm and cold locations. One treatment used Bayvarol® in spring and autumn, the second used Bayvarol® , formic acid and oxalic acid. The third programme only used oxalic and formic acid. The synthetic programme gave better control than the organic/synthetic programme, which gave better control than the organic programme. Varroa was easier to control at the cold site, probably because of lower varroa invasion levels.
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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