New Zealand Beekeeper May 2017

21

NEW ZEALAND BEEKEEPER, MAY 2017

ability to cling to bees and they fall off. Second, it stimulates bees grooming themselves and grooming each other, which also produces mites to fall off. Given the physical mode of action, resistance to sugar dusting is not possible. However, sugar dusting has been said to have a small effect in reducing mite levels and may only be useful as a complementary method together with other methods. Food-grade mineral oil There is very little literature on the use of food-grade mineral oil (FGMO) for varroa control. However, some beekeepers like to use it either by fogging with thermal insect foggers or with cords. FGMO only affects phoretic mites (mites on bees) and it needs to be applied often to have any effect. Regarding the mode of action, some comments on the Internet point to the oil blocking the pores in the mite’s cuticle and preventing gas exchange, which affects breathing. The cuticle of the mite seems to make it more susceptible than bees. If this physical mode of action is correct, resistance is very unlikely. It is possible that the oil also stimulates bee grooming behaviour.

The synthetic chemicals are absorbed by the mite and tend to affect one single protein target, such as the voltage-gated sodium channel (flumethrin and fluvalinate) and octopamine receptors (amitraz). This specificity on single targets makes it highly likely that the mites will develop resistance by mutations in those targets, as has indeed been reported for all of them. In addition, mites can also develop resistance with detoxification enzymes that degrade or get rid of these chemicals from the body. The organic chemicals act by absorption or direct contact and seem to act by physico- chemical effects on more than one target, making them less specific against varroa mites. This is a logical consequence of the fact that these chemicals are synthesized by plants to fight against different types of insects and pests and not against mites in particular. Indeed, thymol seems to act by affecting octopamine, tyramine, and GABA receptors, formic acid disrupts the mitochondria in cells, perhaps as a consequence of low pH, and oxalic acid may also act by affecting mitochondrial function. The action on more than one target or by physico-chemical effects that disrupt cell structures makes resistance to these treatments less likely. In fact, there are no reports of resistance to these treatments. However, alternation with other treatments is still recommended. Finally, the less-popular icing sugar and food- grade mineral oil treatments seem to affect the mite by physical effect due to the direct contact and by stimulating bee grooming behaviours. This means that resistance to these treatments is very unlikely to arise.

A gorgeous frame of honey. Photo: Jo Telfar.

Conclusion The mode of action of different varroa

WE WANT YOUR PHOTOS! The Publications Committee welcomes photos for the journal. Pop a camera in the truck and snap away when you find something interesting. The safest way to supply a digital file is in a high-quality jpeg format. If you’re thinking big (such as a potential front cover photo), these need to be as large as possible (300 dots per square inch (dpi) at the size they are to be used, in portrait format (vertical rather than horizontal). Regular digital photos are only 72 dpi, so are not suitable for the front cover. Please provide a caption and the name of the photographer so we can credit them. Email photos and captions to editor@apinz.org.nz

treatments has not been studied in detail for most treatments. However, we can still get an idea from studies in insects and other mite species. Different treatments have different modes of action: either chemically after being absorbed, physically by direct contact, or by stimulating defensive behaviours from the bees.

Treatment

Mode of Action

Resistance?

Flumethrin/fluvalinate Voltage-gated sodium channel

Yes

Amitraz

Octopamine receptor

Yes

Thymol

Octopaminergic system, tyramine and GABA receptors

Less likely

Formic acid

Mitochondrial disruption, neurotoxic

Less likely

Oxalic acid

Mitochondrial function

Less likely

Sugar dusting

Grooming, affects ability of mites to hold on to bees

Not likely

Food-grade mineral oil

Suffocation, grooming

Not likely

Table 1. Various treatments, their mode of action and likelihood of varroa resistance.

References Complete article with references is available on request from the author: pablo.german@pheromite.com

Made with FlippingBook Annual report