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