Toxic Nectars and Pesticides#
1 . How can the beekeeper tell if bees have been poisoned with toxic nectar?
Similar to pesticide exposure, toxic nectar can cause bees to die inside the hive (on the bottom board), at the hive entrance, or near the nectar source.
2 . What is the main source of toxic nectar in Georgia?
Yellow jessamine (Gelsemium sempervirens) which is often confused with “Confederate jasmine” (which is not toxic to bees). It blooms early during swarm season, kill foragers and can damage or kill developing queen cells.
3 . What are other sources of toxic nectar in Georgia?
Summer titi / Southern leatherwood (Cyrilla racemiflora) which causes “purple brood” (discolored larvae). It is located in the southern part of the state along the coastal region. Mountain laurel (Kalmia latifolia) which is found in North Georgia mountains and is toxic to both bees and humans Privet (Ligustrum spp.) is a very common invasive shrub which is not necessarily toxic but is suspected of producing poor-quality or unpalatable honey
4 . What is “mad honey,” and what plant does it come from?
What are the symptoms?
Caused by grayanotoxins found in nectar from rhododendron species. Symptoms in humans include: dizziness, low blood pressure (hypotension), heart rhythm disturbances (AV block) and is typically not fatal but can be serious. Primarily found in the Himalayas, it is also in the Appalachian region of the US where rhododendron species occur.
5 . Can honey cause botulism in infants?
Yes. Honey can contain spores of Clostridium botulinum, which may grow in an infant’s immature digestive system and produce toxins. However, not all honey contains spores and is safe for breastfeeding mothers to consume since botulism is not transmitted via breast milk
6 . How can botulism in infants be prevented and why don’t older children and adults get botulism from honey?
Do not feed honey to infants under 1 year old. Mature digestive systems contain established gut microbiota that prevent C. botulinum spores from germinating and producing toxins.
7 . About how many pesticide chemicals and formulations exist?
There are roughly 500+ active pesticide ingredients used in agriculture with thousands (10,000+) of formulations existing due to combinations and delivery methods.
8 . How do pesticides affect honey bees?
Most pesticides act as neurotoxins, disrupting nerve transmission. Some cause desiccation, damaging the exoskeleton and leading to dehydration
9 . Are fungicides toxic to bees?
Fungicides are generally considered low in direct (acute) toxicity to Apis mellifera, but they can still harm bees, especially under real-world conditions.
Direct toxicity (acute effects): Most fungicides do not immediately kill adult bees at labeled rates and are much less toxic to bees compared to insecticides. However, some formulations and tank mixes can increase toxicity leading to sublethal effects.
Indirect and sublethal effects (often more important): Even when bees don’t die right away, fungicides can still cause harm by the following:
Synergistic effects: Fungicides can interact with insecticides, making them more toxic than expected
Brood effects: Exposure can reduce larval survival or affect development
Gut microbiome disruption: Fungicides can interfere with beneficial gut fungi and bacteria, affecting digestion and immunity
Navigation and foraging: Some studies show impacts on learning, memory, and orientation which are affected when exposed to fungicides.
Residues in the hive Fungicides are commonly found in pollen and wax Bees are often exposed over long periods of time (chronically), not just during spraying. Residues land on flowers then bees collect contaminated nectar and pollen. That pollen then becomes bee bread and is stored in the hive. The nectar collected becomes honey and the compounds are also accumulated in the wax.
When risk is highest Applications during bloom (when bees are actively foraging) Tank mixes (fungicide + insecticide) Drift or improper timing High-frequency spraying systems (
g., orchards, vineyards)
Bottom Line: Fungicides are not harmless to bees. While they rarely cause immediate death on their own, they can weaken colonies over time, increase the toxicity of other pesticides and contribute to broader stress on pollinators.
10 . Are herbicides toxic to bees?
Most herbicides are not acutely toxic to Apis mellifera at labeled use rates but they can still harm bees indirectly and, in some cases, cause sublethal effects.
Direct toxicity (acute effects) Generally low toxicity compared to insecticides Bees are unlikely to die from typical field exposure Some formulations (especially with surfactants) can increase risk slightly
Indirect effects due to the loss of forage, habitat reduction, which is the biggest issue. Herbicides remove flowering plants (“weeds”) like clover, dandelion, and wildflowers thereby fewer feeding opportunities across the landscape This reduces nectar and pollen availability Leads to poorer nutrition and weaker colonies Particularly important in roadsides, field margins, and urban areas
Sublethal effects similar to fungicide exposure (emerging research) Affect gut microbiota Impair navigation or learning in some studies Interfere with larval development when residues are present in food
When risk is highest Large-scale or repeated applications that eliminate most flowering plants Spraying during bloom even if just targeting weeds Highly managed landscapes, such as grass lawns with little alternative forage
Key takeaways - Herbicides typically don’t kill bees outright, but they can: Starve them slowly by removing food sources Contribute to chronic stress and poor nutrition Add to the combined pressure of pesticides, pathogens, and habitat loss
11 . Are insecticides toxic to bees?
Yes, insecticides are the most toxic class of pesticides to Apis mellifera. They are designed to kill insects, so bees are highly vulnerable.
Direct toxicity (acute effects): Many insecticides can kill bees quickly upon contact or ingestion Exposure routes include direct spray, residues on flowers (nectar and pollen) and contaminated water sources.
Highly toxic groups include: Neonicotinoids (e.g., imidacloprid) Pyrethroids Organophosphates Carbamates
Sublethal effects: Lower doses can still cause serious problems Disorientation - bees can’t find their way back to the hive Reduced foraging efficiency Impaired learning and memory Reduced queen health and egg-laying Weakened immune system
Colony-level impacts Loss of foragers → reduced food intake Poor brood development Increased susceptibility to diseases and parasites In severe cases, colony collapse
When risk is highest Spraying during bloom when bees are actively foraging Drift from arial or tank spraying Dust from treated seeds (e.g., during planting) Tank mixes (can increase toxicity) Repeated or high-rate applications
Unlike fungicides and herbicides, insecticides pose a high and immediate risk to bees. Even small amounts can have lethal or long-lasting sublethal effects, therefore making careful management and timing plans is essential when applying any kind of insecticide.
12 . Is pesticide-related bee kill increasing or decreasing?
Generally decreasing, due to: Reduced use of highly toxic compounds (e.g., many organophosphates) Improved pesticide regulations and labeling Increased adoption of Integrated Pest Management (IPM) However, neonicotinoids are still widely used and remain a concern in some systems.
13 . What are symptoms of pesticide kill in a colony and how is this different from starvation?
Large numbers of dead bees in front of the hive and on the bottom board. Starvation usually presents itself as a number of dead bees between the combs, on the bottom board and heads in the cells. With pesticide kills bees are usually at the entrance and in front of the colony.
14 . What symptoms do individual bees show when exposed?
Agitation or hyperactivity
Trembling or shaking
Difficulty flying
Paralysis
Death
15 . What causes bees to be exposed to pesticides?
Spraying insecticides on blooming plants (primary cause) Drift from a field or plant being sprayed High-risk formulations such as microencapsulated pesticides which mimic pollen particles. These pesticides are collected and stored in hive and cause prolonged contamination and delayed colony death.
16 . How can pesticide kills be avoided?
Formulation matters (most to least hazardous): Microencapsulated > Dusts > Wettable powders > Solutions > Granules
Best practices:
Apply pesticides in the evening when bees are not foraging
Use low-residual insecticides such as solutions or granules
Avoid spraying during bloom
iv. Use formulations that are less persistent in the environment iv. Prevent drift (do not spray if wind > 10 mph) v. Know your insects! Some or most are actually beneficial vi. Be aware that cooler temperatures increase pesticide persistence vii. Colonies within up to 5 miles radius may be affected during forage shortages
Communication is critical. Maintaining relationships with farmers/applicators/neighbors are important.
17 . What should a beekeeper do if pesticide poisoning is suspected?
Remove or replace contaminated comb (especially pollen frames)
Feed sugar syrup
Add brood from healthy colonies
Replace the queen if affected
Avoid using contaminated wax for queen rearing
Move colonies to a new location is poisoning persists
18 . How do genetically modified (GM) crops impact beekeepers?
Some GM crops (e.g., Bt corn, cotton) produce insecticidal proteins. Current evidence suggests low direct toxicity to bees, however: Long-term and sublethal effects are still being studied
19 . What information is found on a pesticide label?
Toxicity measurements (LD₅₀, LC₅₀) Acute vs. chronic toxicity Active ingredient class (e.g., pyrethroid, carbamate, organophosphate, neonicotinoid) Formulation type (dust, granule, solution, etc.) Application guidelines: timing, residual activity, re-entry intervals Pollinator protection warnings Symptoms of poisoning and mitigation steps