Varroa Mites in Honeybees Still a Major Concern

 —by Michael Braverman, Manager Biopesticide & Organic Support Program

The Varroa mite Varroa destructor has been a pest in honeybees in the US since the 1980’s. Varroa mites are a parasite that live on the outside of the bee’s body and attack both adult and developing bees. The mite is consistently considered the primary pest in bees. While there are many theories on the cause of Colony Collapse Disorder, Varroa mite is thought to play a major role. The mite may be small to the eye but in comparison to the bee, it is huge. On a human scale, it has been described as being equivalent to the size of a dinner plate or basketball, sucking out the bee’s hemolymph (blood-like fluids) and injecting viruses. The combination of fluid loss and disease can be devastating to the bee colony. Bees are extremely important in horticultural crops and pollination has been estimated to contribute 13 billion dollars in crop value to fruits and vegetables.


IR-4 has been assisting in the registration of several tools for managing Varroa mite including both conventional products and biopesticides. Just like plant mites, Varroa mites are champions when it comes to developing resistance to pesticides therefore new options for managing this pest are still needed. Several Section 18 registrations (Emergency use) have been approved by EPA over the last several years due to resistance issues including coumaphos (Check-Mite), fenproximate (Hivastan), hops beta acid (HopGuard) and amitraz (Apivar). IR-4 submitted the Section 3 registrations for coumaphos and hop beta acid. IR-4 also helped to get the first formic acid use approved as well as thymol (Api-Life Var) and sucrose octanoate (Sucrocide). Oxalic acid is also of interest to beekeepers, and IR-4 is still attempting to get this registered.

Future developments in varroa mite control may include molecular approaches. An RNAi (RNA interference is explained in detail in IR-4 Newsletter Vol.45 No. 1) to decrease resistance of mites to some pesticides (through reductions in glutathione-S-transferase activity) has been developed but the method of efficiently administering this product is still under development. In addition, it would only overcome resistance issues so a pesticide would still be needed. Other RNAi approaches have been found to be possible in controlling several bee diseases. The fact that Varroa mite can transmit bee diseases (such as viruses) may enable Varroa to spread RNAi based products that manage bee viruses to other bees. Similarly, there has also been more recent evidence that a type of double stranded RNA (dsRNA) fed to honeybees in sucrose feeding solutions can be transferred to Varroa mites when mites suck on bee fluids. Several dsRNA targeting Varroa mites have been successfully transferred to Varroa mite including interference with the Varroa mites skeletal structure and cell death. These are still at the research phase.