Notes from Dewey – September 2023

by Dewey M. Caron, Communications and Content Specialist for the Oregon Master Beekeeper Program

Need a veterinarian?

Beginning in 2017, due to a Food and Drug Administration directive, certain antibiotics we might use to treat bee diseases became subject to a Veterinary Food Directive (VFD) if fed as animal feed or as a prescription from a veterinarian. The antibiotics for American and European foulbrood, oxytetracycline (terramycin) and Tylosin, are included. Furthermore, the FDA directed that veterinarians only provide the VFD or prescription once a working relationship of beekeeper and veterinarian was established.

Undergraduate Samantha Miller did an OSU honors thesis on training veterinarians with Michelle Kutzler (Animal Sciences) and Carolyn Breece and Ramesh Sagili of the OSU Honey Bee Lab. They described their training effort in February 2023 Bee Culture magazine (page 23). There are now 34 veterinarians in 19 Oregon counties that ware interested in serving the antibiotic needs of Oregon beekeepers See this is list at

Dr Sagili – with Dr Elina Nino of UC Davis – has developed a training course of 8 modules for Western Institute for food safety and security (WIFSS). There is $45 fee for the course. It is a great review of bee biology, the foulbrood diseases and the role a veterinarian will play if you wish to use an antibiotic for AFB or EFB. Register at

Continuing this effort at training veterinarians I have assisted Dr Meghan Milbrath of Michigan State in her 3 week “rotation” of vet school students in the honey bee module (3 intensive weeks of bee training). Meghan will be a speaker at the fall Washington State beekeepers meeting in Olympia Oct 7/8. Later in October I will offer a day-long veterinarian beekeeping  training for Vet South in Atlanta, GA.

Illustration Photo Courtesy Mobile vets of Portland

Protecting bees from pesticide damage

One of the “4P’s” of issues that negatively affect bees is pesticides. With older insecticides, acute poisoning often leads to sudden piles of dead/dying bees immediately outside hive entrances. Of concern today are sublethal effects. Chronic, long term exposure effects include reduced immune function, impaired learning/ memory, flight muscle paralysis and the cessation of wing movement. It means foraging bees are unable to properly orient and return to their proper hive.

Recommendations on saving bees include an emphasis on protecting bees and other pollinators when selecting and using pesticides. A new study examining the literature found that many common methods recommended for minimizing the impact of pesticides on bees have almost no scientific evidence to show they are actually effective—even some recommendations included on pesticide labels.  (Shaw, Edward A. and Dara Stanley. 2023. Weak evidence base for bee protective pesticide mitigation measures. Jour, Econ. Entomology. DOI:10.1093/jee/toad118)

It seems the label and recommendations for pesticide users on “mitigation measures” provided to protect bees during pesticide applications are of limited value. Recommendations include spraying at night, using specific nozzles on sprayers, or maintaining buffer or no-spray zones. The study found a mere 34 studies with appropriate research but little in them that support these oft repeated recommendations.  The authors concluded that stronger testing is needed to evaluate which bee-protection measures are truly effective and which ones may be  “conventional wisdom” but not especially useful.

In a different study, Varroa/viral infestations were assayed to determine susceptibility of honey bee workers to pesticides under lab/semi-field conditions. One group of colonies were treated with the miticide Apivar, which resulted in mite-reduced colonies in the fall compared to colonies where mites were not controlled. Workers were collected and tested for susceptibility to five different insecticides. Their susceptibility measure was expression levels of six immune- and physiology-related genes that have been shown to relate to  insecticide susceptibility in honey bees. Actual death rate was not monitored.

The insecticides included contact and oral activity pesticides. The authors did in fact find an association of increased DWV infestation with decreased physiological and immunity-related functions in late-season honey bees.  The bees from colonies with lower mite/DWV infestations exhibited  consistently lower pesticide susceptibility when compared to the bees from colonies without Apivar treatment (i.e. higher mite level bees were considered to be more susceptible to pesticide damage). They concluded there is an interaction of Varroa/viral infestations with insecticide exposure that might increase the stress level of higher mite colonies leading to a potential for heavier bee losses.  They surmise this association is via weakening of immunity and physiology-related genes. (Yu-Cheng Zhu, et. al. 2023. Varroa mite and deformed wing virus infestations interactively make honey bees (Apis mellifera) more susceptible to insecticides. Environ. Pollution.

Dr Andony Melathopoulos is presenting a NAAPC (No American Plant Pollinator Consortium) sponsored webinar September 27th: Drilling Down on EPA Risk Assessment – What is the latest buzz on pesticides and bees? Register via NAPPC or through extension.

Photo: Acute pesticide poisoning symptom by Ellen Topitzhofer