Kristen Healy | 7/19/2016 6:28:47 PM
Honeybees are important for both honey production and pollination services. Approximately one out of every three bites of food we eat relies on bees for pollination, and honeybees contribute to billions of dollars’ worth of pollination services annually in the United States. While the U.S. Department of Agriculture projects the U.S. population to be between 2.5 million to 3 million honey-producing colonies, there have been ongoing concerns regarding population declines and colony collapse disorder (a condition where the majority of honeybees in a hive disappear without any apparent cause). Despite technologies designed to improve bee health, beekeepers are faced with numerous factors – pests, disease and loss of habitat – that can affect the health and well-being of their colonies. In particular, varroa mites and tracheal mites can be devastating to honeybee colonies by reducing the health of a colony, by transmitting pathogens or by causing additional stress to a hive.
In 2013, concern over the effects of pesticides on honeybees came to the forefront of pollinator research. At that time, neonicotinoid pesticides were the main focus of concern because they had recently been banned in Europe based on limited and inconclusive findings. However, the attention toward these particular insecticides had beekeepers concerned about pesticides in general. This provided entomology labs with an opportunity to evaluate the effects of pesticides on honeybee health and mortality. In the summer of 2013 a lab in the AgCenter Department of Entomology received EPA grant funding to evaluate the effects of public health pesticides on honeybees. This opportunity led to establishing a research partnership among the USDA Honeybee Breeding, Physiology and Genetics laboratory in Baton Rouge, local beekeepers, local mosquito control, USDA agricultural engineers and the LSU AgCenter. Involving both beekeepers and mosquito control in this research initiative provided an unbiased evaluation of the data.
In mosquito control, the amount of actual insecticide that gets sprayed is so small that it is like trying to spread a tablespoon of product over an entire football field. While most people are familiar with the visible cloud of product that comes out of a spray truck, these are actually ultra-low volume applications of product mixed with oil or water. The droplets themselves, which are microscopic in size, impinge on the mosquito, exposing it to extremely small concentrations of insecticide. As a result, large-bodied insects are generally not affected by such small doses.
The initial hypothesis was that if mosquito control is done correctly, it should have minimal effect on honeybees. This was based on the assumptions that (1) mosquito control is done at night when bees are in the hive and (2) mosquito control products break down within hours before bees would be foraging in the morning. While some bees may exhibit a behavior known as “bearding” during hot summer nights when bees congregate outside the hive to keep it from overheating, proper ventilation of hives can help reduce this behavior.
Overall findings of the study showed that when mosquito control is done correctly, bees face minimal risk. It is important to note that mosquito control must always factor in protecting the health and well-being of the public. Therefore, AgCenter researchers strongly encourage beekeepers to increase communication with their local mosquito control programs.
There is an old saying, based on a statement by Paracelsus, that “it is the dose that makes the poison.” In toxicology, everything is toxic at a particular concentration. However, whether or not we are actually exposed to that concentration determines the actual risk. In the laboratory, researchers evaluated the relative toxicity of several different public health pesticides to honeybees. This included several pyrethroid and organophosphate pesticides that target adult mosquitoes.
While the researchers were able to determine the lethal concentrations of these pesticides, it is highly unlikely that bees would be exposed to these concentrations in the field. Mosquito control uses extremely small doses of a product designed to target mosquitoes, while having the smallest possible effect on other organisms. Most insects, including honeybees, are much larger than a mosquito and would not be affected by such low concentrations of insecticides.
Semi-field Cage Studies
In 2013 and 2014, AgCenter researchers conducted several semi-field cage studies in Baton Rouge to evaluate the effects of public health pesticides on honeybees. Each trial put out honeybees and mosquitoes at 50-foot intervals up to 300 feet away from the spray truck. At each distance, researchers put out cages of bees, cages of mosquitoes and devices to collect data on pesticide droplets and concentrations. While researchers were able to kill mosquitoes during this trial, they rarely saw any bee mortality.
Even at the closest distance to the spray truck, the trial was unable to kill honeybees with pyrethroid pesticides, which are most commonly used in truck-based applications. Mortality increased slightly with organophosphate pesticides. However, researchers only saw mortality when the highest possible label rate was used and when bees were located within 150 feet of the spray truck.
Additional studies indicate that positioning hives at least 200 feet from the road and orienting them away from the spray would greatly reduce exposure. Therefore, beekeepers should contact their local mosquito control programs to become more knowledgeable about the products used in their programs and how often they are applied.
In the summer of 2014, researchers collaborated with members of the Capital Area Beekeepers Association, who provided sentinel beehives as part of this study. Half the volunteer beekeepers were in areas that received frequent mosquito control, while the other half were in areas that received no mosquito control. As part of this study, researchers evaluated multiple health and mortality parameters in each of the participating bee colonies and found no difference between honeybee colonies within or outside mosquito control areas. In fact, many beehives were located close to roads, and researchers had many spray events during the study.
During the study, the mosquito control program had used both truck-based applications of pyrethroids and aerial applications of organophosphates. However, researchers did not see any increased mortality because of mosquito control. While this was only a single season of data collection, the results suggest that honeybees have minimal exposure to public health pesticides.
Mosquito Control and Public Health Pesticides
Mosquito control programs are the best defense against transmission of mosquito-borne pathogens, such as West Nile virus, Zika virus and Eastern Equine encephalitis virus. Mosquito control involves Integrated Mosquito Management (IMM) techniques that employ strategies that have the greatest impact on mosquito populations while minimizing any effects on the environment.
While most people are familiar with mosquito control spray trucks, they are not aware of the many other management practices used to control mosquitoes. These include using biological control agents that target the immature mosquitoes, conducting surveillance for mosquito abundance and mosquito-borne virus activity, conducting water management projects that help improve the environment while reducing mosquitoes, and incorporating technologies that have the smallest potential carbon footprint. Mosquito control, when done correctly, does an amazing job at reducing mosquitoes and protecting the public from mosquito-borne diseases.
Before modern mosquito control, tens of thousands of individuals in Louisiana lost their lives to yellow fever and malaria, both of which are caused by mosquito-borne pathogens. Thankfully, Louisiana has many parishwide mosquito control districts conducting IMM. A loss of mosquito control programs performing IMM could result in dramatic increases in both nuisance and vector mosquito species. And with current threats from chikungunya and Zika viruses, mosquito control programs that use IMM are essential tools to protect the public, our family and friends, and our pets from mosquito-borne diseases.
Kristen Healy is an assistant professor in the Department of Entomology.
Honeybee on sugar maple flower. Photo by Claudia Husseneder
Entomology graduate student Vivek Pohkrel evaluates a sentinel beehive. Photo by Kristen Healy