Tiny Crustaceans Enlisted to Fight Mosquitoes in New Jersey


(Beyond Pesticides, June 27, 2012)

One county in New Jersey is getting serious about combating mosquitoes this season. Instead of relying on pesticide spraying, which has been shown to not be effective, the Cape May County Department of Mosquito Control is employing 10,000 tiny shrimp-like crustaceans that will eat their way through mosquito larvae in the county’s swamps, roadside ditches and small pools.

The latest weapon in the battle against mosquitoes is barely visible. The crustaceans, known as copepods, are cousins to crayfish and water fleas, and do not get much bigger than two millimeters. They are voracious predators of mosquito larvae. New Jersey recently delivered 10,000 of the tiny shrimp-like crustaceans to Cape May County. They are already being used to fight mosquitoes in Bergen, Passaic, and Morris counties. Ocean County is next on the delivery list and six other counties will follow.

“The days of driving a truck down the street and spraying pesticides are long gone. These copepods can pick up where fish leave off,” according to Administrator Robert Kent, of the state Office of Mosquito Control.

Natural Predators as a Solution for Mosquito Control

New Jersey has used mosquitofish, fathead minnows, killifish, bluegill and other fish to combat the blood-sucking pests in larger waterways. Sometimes this involves digging ditches, not to drain the swamp as in the early days of mosquito control, but to give the fish access to the mosquitoes. Copepods, which eat mosquito larvae but not adult mosquitoes, are meant for smaller freshwater applications, such as roadside ditches, small pools, and near schools where there are strict regulations limiting pesticides. The hope is birds and other wildlife will also move the copepods around.

Peter Bozak, Cape May County’s director of Mosquito Control, set up a test plot with six small water holes. Copepods were put in four of them and left two as control plots. How many mosquito larvae are eaten and at what stage in their development is being monitored. Mosquitoes hatch from eggs and then go through several stages toward adulthood.

“We’re trying to use our native species and take pesticides out of the environment,” Mr. Bozak said.

The county also put some of the copepods in water-filled tires to see how they do in one of the smaller mosquito-breeding environments, and a batch has been applied to a scour hole filled with rainwater at Middle Township High School. According to a study by the New Orleans Mosquito and Termite Control Board, copepods have proved more effective for practical mosquito control than any other invertebrate predator of mosquito larvae. The most effective copepod species have the capacity to kill more than 40 mosquito larvae/copepod/day, typically reduce mosquito production by 99-100%, and maintain large populations in habitat for as long as there is water. However, while copepods by themselves may not eliminate Culex pipiens production or other mosquito species that transmit West Nile Virus, they can reinforce and augment control by other methods.

Least-Toxic and Cost-Effective

Reducing the use of pesticides is one of the big selling points. Copepods are natural and native to New Jersey, though this is the farthest north they have ever been used for mosquito control. New Orleans was the first to use copepods, and it taught New Jersey its system of growing them in a laboratory. New Jersey is only the second state to use them. They are also inexpensive to produce at the state Department of Agriculture’s Philip Alampi Beneficial Insect Rearing Laboratory in West Trenton. It takes about six weeks to make a batch using distilled water and wheat seed as a medium, feeding them paramecium.

Pesticide spraying for mosquito management is widely considered by experts to be the least effective and most risky response to this important public health concern. Pesticides typically used in mosquito spray programs are synthetic pyrethroids and in some cases organophosphates, both of which are associated with a host of adverse health effects, including neurological disorders and cancers. The frequency of pesticide applications required for aerial applications to be effective, combined with the public health risk caused as a result of these applications, makes aerial mosquito spraying campaigns ineffective both in terms of cost and public safety. In fact, the CDC and many local mosquito abatement districts emphasize public education and the control of larval populations as the first line of defense against mosquitoes and mosquito-borne diseases. Additionally, there is no credible evidence that spraying pesticides used to kill adult mosquitoes reduce or prevent mosquito-borne incidents or illnesses.

The ideal mosquito management strategy comes from an integrated approach emphasizing education, aggressive removal of standing water sources, larval control, monitoring, and surveillance for both mosquito-borne illness and pesticide-related illness. The first step in avoiding mosquitoes around your property is prevention. Remove any standing water where mosquitoes can breed around the home, such as potted plants, leaky hoses, empty buckets, toys, gutters, and old tires. When outdoors in the evening, while mosquitoes are most active, the best way to avoid them is to wear long pants and long sleeves and use natural least-toxic mosquito repellents. Burning citronella candles outside also helps repel mosquitoes. It is important to read labels carefully before buying or spraying repellents.