Is Btk Safe for Honeybees?

Education is learning what you didn't even know you didn't know.
Daniel J. Boorstin

 According to the Peninsula Daily News, “State agriculture officials will decide soon whether to propose spraying a biological pesticide over 10,500 acres across seven sites in Western Washington to kill leaf-eating gypsy moths. Washington and Oregon States will be doing a spray program this year (2016). The proposed Washington sites are Kent, N.E. Tacoma, Port of Tacoma, Fife, Milton, Vancouver, Port of Vancouver, Nisqually, Lacey, Gig Harbor and Seattle’s Capitol Hill neighborhood. Washington would conduct three aerial sprayings, seven to 10 days apart, in April. In Oregon, state officials propose spraying in mid-April by helicopter over targeted areas of Forest Park, north Portland and Hayden Island with three treatments.“ 

There is much talk in my community about government aerial spraying for gypsy moth this year. And there’s a lot of fear about aerial spraying of any kind, especially in the beekeeping circles. We beekeepers have enough trouble with neighbors spraying insecticides, combatting known and unknown bee diseases, raising healthy bees with organic methods and winter die off. Now add the element of overhead spraying…aargh! ENOUGH CHEMICALS ALREADY!!

 But wait…we’re talking about Bt here. What is it really?

According to Rodale’s All New Encyclopedia of Organic Gardening (1992) “Microbial insecticides such as Bt and it’s varieties are effective, slow acting pesticides with virtually no harmful side effects and considered non-toxic to mammals.”

In Garden Insects (2004) Whitney Cranshaw writes “Bt is the best known bacterium…and is commonly  used as a microbial insecticide. Several strains exist, each of which affects only certain types of insects that ingest the bacteria or the toxic protein crystal it produces”. 

On the subject of organic beekeeping, Ross Conrad is my go to guy for my beekeeping questions. He is an author and organic beekeeper. For cases of preventing wax moths in bee hive equipment, in his book “Natural Beekeeping” (2007) he touched on the use of Bt for control of wax moth, a highly destructive insect in bee hives.  He writes “Bt has been used safely by the organic farming community for decades… is a bacterium that, when ingested by certain insect larvae, will kill the host…it becomes toxic only when exposed to the unique digestive environment found within the wax worm’s gut. There are no harmful side effects like with chemical (synthetic) pesticides.  Bt is sprayed directly onto the plant’s leaf. The toxin is not produced until the pests eats a leaf upon which the Bt microbe rests, it is safe and non-toxic to animals, humans, and beneficial insects, and it may be used right up until harvest. Also used by organic beekeepers as a safe alternative to moth balls for preventing wax moth infestations in empty hive equipment.” In this case Bt can be sprayed on frames and hive bodies that will be stored for later use. The presence of the bacterium will kill any larvae that hatches and feeds on the wax.

Gypsy moth, today’s subject, is a major pest known to defoliate millions of acres of hardwood forests annually and perpetually defoliated trees means death. WSDA claims gypsy moth control is often necessary to prevent damage in backyards and many urban areas to help stop the spread into neighboring forested areas. Bacillus thuringiensis subspecies kurstaki (Btk) is the variety of insecticide of choice for this insect. Btk is a natural soil born bacteria which biodegrades in sunlight within about 10 days, hence the multiple applications and it will likely be done at night, minimizing exposure to people and animals and for sure honey bees who don’t fly at night or eat leaves. What about the leaf cutter bees, our native pollinators...they wrap their nests with leaves but they do not eat the leaves so this poses no harm to them either. And I don’t see their activity in my garden that early in the spring.

 mindfully.org writes “However, in their natural form, acute toxicity of commonly-used Bt varieties is limited to caterpillars, mosquito larvae, and beetle larvae. Bt var. kurstaki which cause disease in moth and butterfly caterpillars.”

 Yes, Btk would mean death to butterfly larvae too. However the spray applications will be in April. I don’t know if our native butterflies breed in temps that cold here in the Pacific Northwest, and those that migrate from warmer climates to our south don’t arrive till June. I did some research on temperatures necessary for butterfly breeding but couldn’t find a definitive answer. If you know, please drop a line in the comments section. The cooperative extension in Wisconsin suggests “If you are concerned about your butterfly garden plants being sprayed (with Btk), place a tarp over them the night before a spray is scheduled. Then, remove it after spraying is completed.”

 Part of the controversy also lies in the fact that caterpillars, larvae and even moths are a food source for birds. While the infected larvae won’t be harmful to birds, the lack of their populations could represent a decline in a food source for birds.

 The gypsy moths found in Washington and Oregon are two non-native species (European and Asian) of insects that have the potential to devastate our forested lands. They have been brought here inadvertently by international trade. In cases like this we must pick the lesser of two evils and I think a timely and occasional spray with an organic control as deemed necessary when populations show sustained increase is prudent. Yes, you will find extreme cases of human illness due to overexposure if you dig deep enough online but I think by and large it’s a safe choice considering the other alternatives. The cases I found were due to overexposure by splashing large quantities of the liquid on themselves as opposed to a focused spray or drift. Naturally if you are highly sensitive, it is suggested that you stay indoors during the spraying.  Maps of proposed spray areas are published online in states that I found using this method, but do keep in mind drift can enlarge targeted areas.

 My personal opinion? I am not a chemist or a scientist. I’m an organic gardener and beekeeper. I use integrated pest management (IPM) practices. I’m sick to death of all the synthetic chemicals in the world and I use natural, organic methods that include biological controls when I have an infestation that the birds and other predators are not controlling. Bt is one biological control that I have used many times. I’ve been using Bt to combat cabbage moth for years. And I think I’m safe to say, most if not all organic farmers have been using Bt to control leaf eating worms and larvae for eons. The way it works is topically. The bacteria adheres to the outside of the leaf and when the larvae eats the leaf it ingests the bacteria. Bt does not penetrate the leaf so will not be effective on leaf miners. Nor is it effective on adult moths. The larvae must be young. It does break down and does not stay of the leaf, so in the case of my cabbage moths, who lay eggs all summer on all brassicas, I spray weekly, in the evenings all summer.

 The method of Btk is proven effective and the least toxic available, so is prudent and organically approved.  After all, the goal of organic farming is to use the least toxic method to control pests and disease. Btk is far less toxic than the synthetic chemical choices out there.

 In Bloom In My Garden Today: crocus, Erysimum ‘Rysi Moon’, Heath (Erica carnea ‘springwood white’), Sarcococca confusa, Hellebore, Galanthus elwesii (snowdrops), viola, pansies

 Author’s photo of my bees