NC State University

Information & Advice

Protecting Honey Bees During Mosquito Spray Programs

Parts of North Carolina will soon be sprayed with insecticides for the purpose of controlling mosquitoes. Mosquitoes must be controlled in order to reduce the public health risk posed by the large numbers of mosquitoes breeding in stagnant water left by heavy rains. Mosquito numbers have increased dramatically due to the conditions left by heavy rainstorms. The increased risk of mosquito carried encephalitis and the large numbers of mosquito bites demand human intervention to control these pests.

Problems may arise if these insecticides come into contact with honey bees. Honey bees are susceptible to many insecticides, and in fact pesticides are a major cause of honey bee deaths. The flooding in many areas of North Carolina has already resulted in substantial colony losses for many beekeepers, so it is especially important to reduce the impact of the present mosquito program on the remaining honey bee population.
In the past twelve years, the number of managed and feral (wild) honey bee colonies in the U.S. and in North Carolina has been dramatically reduced. A series of introduced pests have eliminated about 1/3 of the managed colonies and almost all feral colonies.

Public awareness of the importance of honey bees is growing. Besides providing the beeswax, honey, propolis, bee pollen and royal jelly that are the basis for countless businesses, honey bees are essential for producing a substantial portion of our agricultural crops. As pollinators, honey bees are unsurpassed in their service to farmers producing fruits and vegetables such as apples, cucumbers, squash, melons, blueberries, pears, etc. Without a large and steady supply of bee colonies, commercial growers would not be able to produce these crops, and their businesses would fail.

The mosquito control program will include ground as well as aerial applications. Adult mosquitoes will be targeted as well as immatures in the water. You are encouraged to look through the links below to get a better idea of what exactly will be taking place and to get information about what you personally can do to minimize inadvertent bee kills.

Conditions that limit inadvertent bee kill during mosquito spray operations

  1. Consider pesticide toxicity to bees. Sumithrin (Anvil) is relatively safe. See the Pesticide Information page on this website.
  2. Ground applications are safer than aerial applications. Drifting is greatly reduced using ground applications.
  3. Consider using Ultra Low Volume applications; these are usually safe for bees. Again, refer to the Pesticide Information page of this website for more information about pesticide safety.
  4. *Time of Day may be the most important consideration.* Most bees will be back in their hives after 3:00 p.m. Pesticides should be applied in late afternoon or early evening for best results in reducing bee kill and maximizing most mosquito spray programs.
  5. Consider the weather: There is little bee flight at temperatures of 65 degrees F or below. There is little bee flight on windy days with sustained wind at 10 mph or gusts of at least 15 mph. There is little bee flight in rainy conditions.
  6. Notify Beekeepers. Release information through the media and through individual contacts. Contact us to obtain a mailing list of beekeepers.

Reducing the Risk of Pesticide Poisoning to Honey Bees

Identify Yourself

The agencies involved in the mosquito spray program have an interest in keeping our honey bees safe. You are encouraged to contact your local county Cooperative Extension office or your local county health department. Let them know that you have colonies and are concerned about the dangers of the mosquito control spray program. Be prepared to give information for locating your apiary or apiaries on a county map. If the spray applicators don't know where you are, they may very well spray your hives.

Cover or Move Hives

The most practical and useful action for those concerned about bees being exposed to the mosquito spray is to cover their beehives. This should be done with wet burlap or other breathable material. The entire hive should be covered to prevent pesticide drift onto the hive. It is especially important to cover the entrance to prevent foragers from going out to contact the poison in the air, on flowers or in water. The material should be breathable to allow fresh air to penetrate, and damp to keep the colony from overheating. In typical autumn weather, it is safe to confine a bee colony in this way for 2 days. Though it may not be possible, moving beehives to a location where toxic pesticides are not being applied is another solution. If you do move hives, be sure to move them at least a mile away to prevent bees from attempting to return to their previous location.

Time of Day

The pesticide applicators will be advised to spray near dusk, or twilight, because that is the time when adult mosquitoes are active and most vulnerable to pesticide spray. Other advantages to spraying in the evening are that the cooler temperatures will keep the pesticide near to the ground where it will do the most good, and less windy conditions experienced in the evenings will reduce pesticide drift. (The applicators will be advised not to spray if it is very windy). Applications late in the day also allow the entire night and early morning for the poisons to decompose before honey bees begin to fly again the next day. It is useful to know that most bee foraging stops when the wind exceeds 20 mph, or if the temperature is below 65 degrees F. This evening spray is very good for beekeepers because the vast majority of bees will be inside the hive and not out where they could contact poisons in the air, on flowers, in water etc.


Different formulations of the same chemical are different in their danger to honey bees. In general, heavier formulations drift less and pose less danger. Also, ground applications drift less and are safer than aerial applications.

  1. "Dusts" almost always present the most drift problems of any pesticide formulation and are generally more dangerous to bees than are sprays or granular applications.
  2. Spray formulations are usually safer to bees than are dusts but there are differences among the spray formulation types. Generally water soluble formulations are safer than are emulsifiable formulations, and fine sprays are less dangerous than course sprays.
  3. Granular applications are generally the safest formulations from a drifting standpoint and the accidental killing of bees. This use should be considered if a granular formulation is suitable for destroying the target pest. Unfortunately, this formulation is not suitable for area-wide mosquito control.
Keep Informed

Information on mosquito spray programs may be listed in local newspapers, or on local radio and television programming. Though you are undoubtedly concerned about your bees, remember that bees are just one consideration in the mosquito spray program.