Pesticide Lethal Dose Considerations

Pesticide Herbicide Fungicide: "cide" on a word means "an agent that destroys or inhibits growth"

In my university studies about bees, we are encouraged to share the following information gleaned from current research as of 2024 from the EPA website and the National Pesticide Information Center. I am not an expert, but it does not hurt to motivate thoughtful landowners to do some further study when choosing to use pesticides, herbicides, and fungicides.

Let's bee better informed when a pest control company says their chemicals are safe. Ask them "safe for what?" In the U.S. we primarily rely on labels to explain appropriate use by applicators rather than ban lethal products, so the fact that you can buy it over the counter or hire someone to use it does not mean it is “safe”. EPA approved does not mean “safe”. Ask specifically what chemical they are using and what LD50 the dosage is based on. Make sure they know your concerns as this may influence their application routine.

LD50 means "Lethal Dose" or "how much of this stuff will kill 50 percent of an animal species either on contact (acute), after a few days (chronic) as a coating on plants (residual), as a consequence, for example, of bees bringing contaminated pollen back to feed their young and affect their ability to function, (sublethal), or if it interacts with other chemicals or substances (synergistic). The figure is usually based on weight. LD50 for mice is not the same for bees. The LD50 for mosquitos or ticks vary from bees.

In addition, the concentration of a particular chemical that kills 50% of a species in the same time-period is known as the Lethal Concentration (or the LC50). The higher the LD50 or LC50 the more it takes to kill. The less LD50 or LC50 the less chemical it takes to kill. The LC50 for mice will obviously be different for bees.

If you are concerned about your bees or native pollinators, or other pets or livestock, look up the LD50 and LC50 for the chemical in use for the specific animal you need to protect and the application precautions. Don't rely completely on the applicator hired to do it, but if they know your concerns they should make recommendations. Oddly, most info out there does not understand that bees bite and collect plant materials other than pollen and nectar and need water to survive, so the residual numbers are important for bees and other pollinators.

Neem oil: The active ingredient in neem oil, azadirachtin, disrupts the endocrine system of insects and prevents them from reproducing or feeding. Neem oil also affects the nervous system of honeybees, causing paralysis and death. I've seen this happen to a honey bee colony placed with confidence by a beekeeper on an organic farm and it is heartbreaking.

Here are some EPA approved insecticides used for Mosquito control with some indicators of their toxicity:

Organophosphates

Malathion - is highly toxic to bees, whether from direct contact, contact with foliar residues, or contact with residues on pollen. The honey bee topical LD50 is 0.71 μg/bee. Malathion is toxic to other beneficial insect species, and very highly toxic to aquatic invertebrates. The LC50 for worms is 613 mg/kg of soil.

Naled - moderately to highly toxic when eaten by birds such as mallards, Canada geese, and sharp-tailed grouse. Mallards also showed a reduction in egg production, egg survival, and hatchling survival following long-term repeated exposures to naled. Naled is also highly toxic to bees through direct contact (LD50 of 0.48 micrograms/bee). Indirect contact with plants was found to be highly toxic one hour after application and practically non-toxic one day after application. During a field application, naled was low to moderate in toxicity to honeybees after three hours.

Synthetic Pyrethroids
At high doses, twitching, paralysis, and death are observed...kill a wide variety of insects instead of selectively targeting specific pest species. For this reason, many are highly toxic to honey bees and other beneficial insects. Low doses can impair development, reduce foraging behavior, and hinder foragers’ ability to find their way home, and have all been shown to impair motor functioning in bees in various studies.

Conclusion
There is a lot more information on how the inert ingredients vs active ingredients of a pesticide, herbicide, or fungicide impact our natural world. Look to reputable, peer reviewed research projects for answers. With honey bees, for instance, even the inert ingredients that help do things like thin a chemical to help it move through a sprayer, not required to be on the label, can be lethal.

Athena Contus ~ Athena’s Bees
Carroll County Adult Education
Cornell University Certified Master Beekeeper
University of Montana Certified Master Beekeeper

Updated: My Hive Setup

Learning to be the perfect beekeeper can be a life long pursuit ending in: "Oh well, I tried my best." I still experiment with overwintering methods of management after keeping bees 16 years in the Sandwich Mountain Range of New Hampshire U.S.A.; but for the most part this little history of my learning curve stands true. Important to note: my efforts to raise bees free of treatment for varroa means choosing smaller colonies producing less honey but continues to result in more survival success than most folks over the long haul. (Research this route carefully and stay current with reliable sources of instruction.)

From Blogger March 2017 with a few edits for clarity: 

My bees thrive well in an eight frame hive set up here in Northern New Hampshire. I tweaked the ten frame hives I'd invested in so heavily until finally, several years ago, gave in to this narrower concept. 

My bees wanted to go up, following the heat of the cluster in winter. Honey left on the outskirts of a super that would tempt them to break cluster to reach, was ignored once cold weather set in. Sometimes colonies starved.

The diseases I was seeing in my failed ten frame colonies screamed of moisture and poor ventilation; so I utilized the "varroa" screened bottom board to help with airflow. William Bonny's old book on "Hive Management" agreed with a local farmer's advice to keep a pine needle filled super on top during winter to catch moisture. That book also introduced me to homasote board. 

Even that I tweaked: the board became soaked with bee-respiration - solved by adding some sticks or a stone under the telescoping cover to allow airflow to wick it off. The pine needles are now held up by 1/2 inch hardware cloth to keep debris from falling in, but the bees can still come up and "get a drink."

All these changes begun to work well, but I feared the brood box would be exposed to abrupt airflow sitting there on that screened bottom, especially going into - and coming out of - winter. 

The discovery of a swarm control component called the "slatted rack" was the next stop in my beekeeping journey. I found it perfect for buffering the brood box from the outside air. It also gave the chilly spring foragers a place to hang out in increment weather instead of crowding up into the nursery. 

The bees loved it and so do I. Setting all this on top of two leveled chimney stones cut off any direct cold air flow. It also seemed high enough off the ground to discourage skunks from scratching at the door. 

Eventually my mouse guard also deterred skunks when changed to hardware cloth cut so prongs would expose their paws to pricks. So did the new solar powered fencing with lower wires.

After about three years of failure with southern packages and nucs queened from southern climates, I began to choose northern honey bees, raised farther north than I was. I'd drive as far as I had to go. This was to try and insure overwintering survival with our uniquely short nectar flows in my mountain intervale - only five and a half months - late April to the end of September. 

In that many years the trees had also grown a few feet higher in my apiary, putting every colony in full shade. Also by that time every wasp in area knew where my hives lived. Two colonies were killed. A move had to be made. 

About then a neighbor in failing health invited me to place hives in view of his window. He lived long enough to take pleasure for a few seasons watching my bees enjoy full sun on several acres of wild forage with a northern wind break of wonderful nectar and pollen producing trees. Then the landscaped changed from fallow fields to a haying operation. Another move was required to insure good forage for my bees.

These savvy acclimatized honey bees now filling my narrow hives, along with the changes made to my apiary set up, began to bring joy instead of angst to my beekeeping. I have had a few summer losses due to normal events, including beekeeper-too-busy-itis during swarm season, however, no losses winter through mid-summer like I was experiencing before. I do see mites, but not high counts others are dealing with. Most importantly, I see no diseases, and previous to these changes I think I saw them all except AFB.

I've hung in there as a beekeeper by focusing on the specific issues facing my colonies instead of trusting a lot of disparaging advice to blame every beekeeping malady on varroa mites; solve every problem with treatments. I've also looked to successful northern bee school teachers and scientist, like New England's own Professor Thomas D. Seeley for insights and Vermont's Kirk Webster among others. To improve my understanding of honey bee biology as of 2023 and stay current with modern management practices I've completed both the University of Montana and the Cornell University Master Beekeepers course of study.

Mostly I've trusted my gut. Not out of stubbornness, necessarily. On some level, though not a scientist, my ongoing studies in honey bee biology seem to say that, given a good home with good natural nutrition, bees acclimated to their climate & familiar with the area forage should be able to thrive where they live, dependent primarily on the wonderful gifts millions of years of evolution have bestowed on them.

I believe this focus has encouraged my continued research, participation in educational opportunities, and brought me satisfaction with small successes that keep me in a very difficult and expensive quest. 

I've been uncertain much of the time with my choices. I've bought miticides or antibiotics - then never had the nerve to go through with treatments. In the end, trusting my gut, paying attention to my bees, and enjoying the occasional validation of science, has so far won the day. 

I didn't know I was this person... this "bee-scientist"; I just wanted to be a beekeeper. 

Fortunately, honey bees are a rather brilliant, persistent little species. They are determined to pull us in, teach us their needs and hopefully, in exchange for a little honey, beauty, fascination, and food, survive to use a few million more years of the amazing gifts of evolution they are so marvelous at utilizing even in a dramatically changing world.

-Please always consider the dates on my posts. Some outdated information can get overlooked but I try my best to take those posts down and don't mind hearing from you about anything puzzling.