Why Millions of Bees Died After Spraying for Zika Mosquitoes, and How to Prevent It

Why did millions of bees die after spraying for Zika mosquitoes? In August 2016, Dorchester County, South Carolina, sprayed the insecticide naled from aircraft between about 6:30 and 8:30 a.m., when honeybees were already out foraging. Naled is highly toxic to bees on contact, and one apiary reported losing about 2.5 million bees in 46 hives. Field studies show that spraying at night, when bees are in their hives, largely avoids this harm.

The summer of 2016 brought fear about Zika, a mosquito-borne virus that can cause severe birth defects when pregnant women are infected. Local transmission had just been confirmed in Miami, and health officials across the South were under pressure to act. In Dorchester County, after four travel-related Zika cases were reported, officials ordered the county’s first aerial spraying with naled. The next day, beekeepers found their hives silent and the ground covered with dead bees. The episode became a national example of how mosquito control and pollinator protection can collide, and of how timing and communication can prevent that collision. This article explains what happened, how naled affects bees and people, what research says about spraying safely, and how communities can control mosquitoes while protecting pollinators.

What Happened in Dorchester County?

On Sunday, August 28, 2016, an aircraft sprayed a naled-based insecticide over parts of the Summerville area of Dorchester County between roughly 6:30 and 8:30 in the morning. As public radio reported at the time, beekeepers found millions of dead bees afterward; Juanita Stanley of Flowertown Bee Farm and Supply said her bee yard looked as if it had been nuked and reported losing more than 2 million bees, a figure local news put at about 2.5 million in 46 hives. Contaminated hives, honey, and equipment had to be destroyed. The county had posted notice of the spraying online and through local media about two days earlier, but several beekeepers said no one contacted them directly, so they did not cover or move their hives. County officials apologized, suspended further aerial flights, and said they would review their procedures.

How Toxic Is Naled to Bees?

Very toxic on direct contact. Naled is an organophosphate insecticide that works by disrupting the nervous system, and it is used mainly as an ultra-low-volume spray that kills adult mosquitoes on contact before breaking down quickly in the environment. A 2026 laboratory study in Environmental Science and Pollution Research by Barascou and colleagues tested four mosquito-control ingredients and their commercial products on adult honeybees. Naled was the most toxic active ingredient when bees ate it, and the naled product Dibrom was the most toxic formulated product by mouth and among the most toxic on contact. By contrast, a pyrethroid product and the biological larvicide Bti showed low toxicity and risk to adult bees. This is why naled labels advise against application when bees are actively foraging.

Can Mosquito Spraying Be Done Without Killing Bees?

Field studies suggest it can, when done correctly. A 2018 field study in PLoS One by Pokhrel and colleagues placed sentinel beehives inside and outside areas treated with routine truck-mounted ultra-low-volume pyrethroid sprays. Over seven weeks, there were no significant differences in bee deaths, colony health, or detoxification enzyme activity between sprayed and unsprayed areas. A 2025 Florida study in Chemosphere by Barascou and colleagues placed 15 colonies at sites treated three to five times over three months with mosquito control products, including naled applied by truck and aircraft and the larvicide Bti, and 15 colonies at untreated sites. Low residues turned up in hive materials, but colony mortality and strength did not differ between treated and untreated sites. Both studies point to the same lesson: with proper timing and application rates, routine mosquito control and beekeeping can coexist.

Is Naled Spraying Safe for People?

At the low rates used for mosquito control, the EPA has concluded that naled does not pose unreasonable risks to people, partly because it is applied in tiny droplets and breaks down within hours to days. Questions remain about higher or repeated exposures. A 2017 study in Environment International by Monica Silver and colleagues measured 30 organophosphate pesticides in umbilical cord blood of infants in China, where naled is used in agriculture. Higher prenatal naled levels were associated with slightly lower fine motor scores at nine months, though the exposures came from farming and diet, not mosquito control, and the effects were small. These findings are one reason some residents opposed aerial spraying in Puerto Rico and elsewhere. Staying indoors during spraying and washing produce from home gardens afterward are simple precautions recommended by many health departments.

Why Did Officials Spray in the First Place?

Because Zika posed a real threat to pregnancies. A 2023 review in Birth Defects Research by Gilbert and colleagues at the CDC describes how Zika was recognized as a cause of severe microcephaly and other brain defects in 2016, after outbreaks in French Polynesia and Brazil and among travelers. When local transmission appeared in Miami that summer, officials there tried ground spraying first and found it had limited effect on Aedes aegypti, a mosquito that breeds in small containers around homes. A CDC report in MMWR by Likos and colleagues described how aerial naled spraying over about 10 square miles, alternated with aerial application of the biological larvicide Bti, was followed by no additional local cases in the area, with no increase in emergency visits for breathing problems. In Dorchester County, by contrast, the four reported cases were travel-related, and no local transmission had been identified, which made the decision to spray from the air more controversial.

What Is the Best Way to Control Mosquitoes?

Integrated mosquito management combines several tools, with spraying of adult mosquitoes as one part rather than the first resort. The foundation is surveillance, trapping and testing mosquitoes to find where risk is highest, and source reduction, eliminating standing water in containers, gutters, tires, and drains where larvae grow. Larvicides such as Bti, a bacterium that kills mosquito larvae but has low toxicity to bees, people, and most other wildlife, target mosquitoes before they can fly. Adult mosquito sprays are used when surveillance shows disease risk or very high mosquito numbers, ideally applied at dusk or night when bees are in their hives, with advance notice to beekeepers.

How Do Mosquito Control Methods Compare for Bees?

Method	How it works	Risk to bees
Removing standing water	Eliminates breeding sites	None
Bti larvicide	Bacterial toxin kills larvae in water	Low in laboratory and field studies
Truck spraying at night	Ultra-low-volume droplets kill flying adults	Low when bees are in hives
Aerial naled at dusk or night	Covers large areas quickly	Lower; notify beekeepers to cover hives
Aerial naled in daylight	Same, while bees forage	High; caused the Dorchester losses

What Can Beekeepers Do to Protect Their Hives?

Register with local mosquito control programs and state apiary or pesticide sensitive-site registries where they exist, so you are notified before spraying. Follow county announcements and social media during mosquito season. When spraying is scheduled, close hive entrances overnight or cover hives with wet burlap or breathable sheeting during the application window, making sure colonies have ventilation and water, especially in heat. Keep records of hive locations and strength, which help with any claim for losses. Building relationships with mosquito control officials before a crisis makes it more likely that schedules can be adjusted.

Why Do Health Agencies Take Mosquitoes So Seriously?

Because mosquitoes spread several serious diseases in the United States and worldwide. West Nile virus, spread mainly by Culex mosquitoes, causes cases in nearly every state each year, and a small share of infected people develop dangerous brain inflammation. Aedes mosquitoes can spread dengue, chikungunya, and Zika, and local dengue transmission has been reported in Florida, Texas, and other southern states in recent years. Globally, mosquito-borne diseases cause hundreds of thousands of deaths each year. These risks explain why counties maintain mosquito control programs and sometimes act quickly when cases appear, and why the goal is to manage mosquitoes in ways that protect pollinators rather than to stop mosquito control altogether.

How Can Communities Balance Public Health and Pollinators?

Practical policies make both goals achievable. Mosquito control programs can keep up-to-date maps of registered apiaries, send direct alerts by text or phone before applications, schedule adult spraying for dusk or nighttime whenever possible, and prefer larvicides and source reduction as first-line tools. Beekeeping associations can encourage members to register hives and share contact details with local programs. State agencies can investigate suspected bee kills promptly and publish what went wrong so others can learn. Public health officials can explain the reasons for spraying and the precautions taken, which builds trust and reduces conflict when urgent action is needed.

What Can Residents Do to Reduce Mosquitoes Without Spraying?

Most mosquitoes that bite around homes, including Aedes aegypti, breed within a short distance of where they are found, so household action matters. Once a week, empty or scrub containers that hold water, such as flowerpot saucers, buckets, toys, birdbaths, and pet dishes. Clean gutters, cover rain barrels with screens, and fill tree holes. Use window and door screens, wear long sleeves in the early morning and evening, and use EPA-registered repellents such as DEET, picaridin, or oil of lemon eucalyptus. Neighborhood cleanup campaigns can reduce the need for spraying, and reporting standing water on public property helps local programs target their efforts.

Why Use Naled Instead of Gentler Products?

Naled kills adult mosquitoes quickly, can be applied from aircraft to cover large areas in a short time, and breaks down rapidly afterward. Some Aedes aegypti populations, including in parts of Florida, have developed resistance to pyrethroids, the other main class of adult mosquito sprays, which leaves organophosphates such as naled as one of the few options that still work against them. During an outbreak, speed matters, and aerial spraying can reach backyards and neighborhoods that truck sprays miss. The trade-off is higher toxicity to bees and other insects on contact, which is why timing and notification are so important when naled is chosen.

Do Wild Bees and Other Pollinators Face the Same Risk?

Yes, and they cannot be protected the same way. Beekeepers can cover managed hives, but wild bees, butterflies, moths, and other beneficial insects that are active when spraying occurs have no such protection. Many native bees nest in the ground or in plant stems and forage at different times of day than honeybees, so timing that suits honeybees may not protect every species. Spraying at night and limiting adult mosquito spraying to times of genuine disease risk reduce the impact on these wild pollinators, which are important for wild plants and many crops.

Do Beekeepers Get Compensated for Spray Losses?

It depends on where they live and the circumstances. After the 2016 spraying, Dorchester County opened a call center to collect reports of losses, and the incident led to public discussion about responsibility. Compensation for pesticide-related bee losses is not guaranteed in the United States and may require insurance claims, negotiation with local governments, or legal action. State pesticide regulators investigate suspected bee kills, and documenting losses quickly with photos, samples of dead bees, and hive records improves the chances of a fair outcome. Prevention through direct notification remains far better than seeking compensation after the fact.

How Did Other Places Handle Naled During the Zika Outbreak?

Responses varied. Miami-Dade County used aerial naled spraying combined with Bti larviciding in 2016 and saw no new local cases in the treated area afterward, though some residents protested. In Puerto Rico, where Zika spread widely, officials faced strong public opposition to aerial naled spraying and turned instead to other measures, including household container removal, larvicides, and later releases of mosquitoes carrying Wolbachia bacteria in pilot programs. The contrast shows that communities weigh the same evidence differently depending on local risk, trust in authorities, and concerns about chemicals, and that public engagement shapes which tools are accepted.

Are Mosquito Sprays a Major Cause of Bee Decline?

They are an occasional, local threat rather than the main driver. Large-scale honeybee losses are linked mostly to the varroa mite and the viruses it spreads, poor nutrition, habitat loss, and agricultural pesticides such as neonicotinoids, as explained in our articles on honeybee colony losses and neonicotinoids and bees. Mosquito control incidents like the one in Dorchester County are dramatic but usually tied to a specific application error, such as daytime spraying without notice. Because these incidents are preventable, they offer a clear opportunity for better coordination between public health agencies and beekeepers.

What Changed After the Dorchester County Incident?

The incident drew national attention and prompted the county to apologize, pause aerial spraying, and review its procedures, including how it notifies beekeepers. It also became a frequently cited case in discussions among mosquito control agencies, beekeeping associations, and regulators about timing applications for dusk or night and maintaining registries of hive locations. The event showed that public notice on a website is not enough when a specific group, such as beekeepers, needs direct warning to protect their livelihoods.

Are There Alternatives to Chemical Spraying for Aedes Mosquitoes?

Several are being used or tested. Releasing male mosquitoes engineered or infected with Wolbachia bacteria can shrink populations or reduce their ability to spread viruses; our article on genetically modified mosquitoes describes trials in Brazil and the Florida Keys. Traps that attract egg-laying females, community container cleanups, and improved housing with screens also reduce bites. These approaches target the specific species that spread Zika, dengue, and chikungunya and pose little or no risk to bees.

Common Myths

“All mosquito spraying kills bees.” Field studies found no colony harm when spraying was done at the recommended times.

“The bees died because naled lingers for weeks.” Naled breaks down quickly; the deaths came from contact during daytime foraging.

“Spraying was useless against Zika.” In Miami, aerial naled with larvicide was followed by an end to new local cases in the treated area.

“A website notice is enough warning.” Beekeepers need direct notification to protect hives.

“Larvicides are as harmful to bees as adult sprays.” Bti showed low toxicity to bees in laboratory and field studies.

Key Terms

Naled: An organophosphate insecticide used to kill adult mosquitoes.

Ultra-low-volume spraying: Application of tiny droplets that drift and contact flying insects.

Bti: Bacillus thuringiensis israelensis, a bacterial larvicide that kills mosquito larvae.

Integrated mosquito management: A combined strategy of surveillance, breeding-site removal, larvicides, and targeted spraying.

Aedes aegypti: The main mosquito species that spreads Zika, dengue, and chikungunya.

The Bottom Line

The 2016 bee kill in Dorchester County, South Carolina, where one apiary reported losing about 2.5 million bees, happened because the bee-toxic insecticide naled was sprayed from aircraft in the morning, after bees had left their hives, without direct warning to beekeepers. Laboratory tests confirm naled is highly toxic to bees, but field studies show properly timed mosquito control does not measurably harm colonies. Zika is a real threat to pregnancies, and targeted spraying combined with larvicides helped stop local spread in Miami. Integrated mosquito management, night spraying, and direct notice to beekeepers protect both people and pollinators.

Frequently Asked Questions

Why did millions of bees die in South Carolina in 2016?

Dorchester County sprayed the insecticide naled from aircraft between about 6:30 and 8:30 a.m. on August 28, 2016, to control mosquitoes after four travel-related Zika cases. Bees were already foraging, and naled is highly toxic to bees on contact. One apiary, Flowertown Bee Farm, reported losing about 2.5 million bees in 46 hives.

Does mosquito spraying always harm bees?

No. Field studies in which mosquito sprays were applied as recommended found no significant differences in honeybee deaths or colony strength between sprayed and unsprayed areas. Harm is most likely when bee-toxic products such as naled are sprayed in daylight while bees are foraging, or when beekeepers are not warned to protect their hives.

Is naled dangerous to people?

At the low rates used for mosquito control, the EPA has concluded naled does not pose unreasonable risks to people, and it breaks down quickly. A Chinese study linked higher prenatal naled exposure from farming and diet to slightly lower infant motor scores, so some caution is reasonable. Staying indoors during spraying is a common recommendation.

How can beekeepers protect hives from mosquito spraying?

Register hive locations with local mosquito control programs and state sensitive-site registries, monitor spray announcements, and cover or close hives during scheduled applications while keeping them ventilated and supplied with water. Direct communication with mosquito control officials before the season helps ensure spraying is timed for dusk or night when bees are in their hives.

What is the safest way to control mosquitoes?

Integrated mosquito management: monitor mosquito populations, remove standing water where larvae grow, use larvicides such as Bti, and reserve adult mosquito sprays for times of real disease risk, applied at dusk or night. Households can help by emptying containers weekly, using screens, and wearing EPA-registered repellents.

References

1. Barascou L, Ellis JD, Jack C, et al. Mosquito larvicide and adulticide impacts on adult western honey bees (Apis mellifera) in in vitro cage studies. Environmental Science and Pollution Research. 2026;33(16):7734–7752. PMID 42084685
2. Barascou L, Rawn D, Qualls WA, et al. The effects of mosquito larvicides and adulticides applied via truck-mounted and aerial spray on western honey bees. Chemosphere. 2025;392:144741. PMID 41138637
3. Pokhrel V, DeLisi NA, Danka RG, et al. Effects of truck-mounted, ultra low volume mosquito adulticides on honey bees (Apis mellifera) in a suburban field setting. PLoS One. 2018;13(3):e0193535. PMID 29494661
4. Silver MK, Shao J, Zhu B, et al. Prenatal naled and chlorpyrifos exposure is associated with deficits in infant motor function in a cohort of Chinese infants. Environment International. 2017;106:248–256. PMID 28602489
5. Gilbert RK, Petersen LR, Honein MA, et al. Zika virus as a cause of birth defects: were the teratogenic effects of Zika virus missed for decades? Birth Defects Research. 2023;115(3):265–274. PMID 36513609
6. Likos A, Griffin I, Bingham AM, et al. Local mosquito-borne transmission of Zika virus: Miami-Dade and Broward Counties, Florida, June–August 2016. MMWR Morbidity and Mortality Weekly Report. 2016;65(38):1032–1038. PMID 27684886
7. WWNO / NPR. County sprays for mosquitoes but accidentally takes out millions of bees. September 2, 2016. wwno.org

Last updated: October 10, 2026