Pesticides for Boll Weevils

Malathion

• Malathion is a broad spectrum pesticide most commonly used in government mosquito spraying programs. For cotton crops, sprayers on slow-moving trucks apply the malathion as they drive about the fields or crop dusters spray the pesticide. To kill boll weevils, apply malathion in late summer or early fall at a dosage of 10 to 16 oz. per acre of land. This is only for fields known to have an infestation of boll weevils -- don't use it as a preventative because of the potential health risks to people.

Grandlure

• Applying pesticides can be tedious work. Farmers and scientists knew that baited traps to lure adult weevils to their deaths would be much easier and potentially less damaging to the environment. Traps help indicate which fields need spraying and which to leave alone. When scientists successfully reproduced the male boll weevil sex-attracting pheromone in 1968 and gave it the brand name grandlure, they began using it in traps. The traps combine grandlure and malathion. Grandlure brings fertile female adults to the trap and malathion kills them.

Banned

• One highly successful pesticide for boll weevils was dichlorodiphenyltrichloroethane or DDT. It also nearly wiped out the common bedbug. Although developed in the late 1800s, it was not discovered to be such an effective insect killer until 1939. DDT began use on North American commercial farms and orchards after World War II. However, DDT proved to kill many other species other than bugs, so the Environmental Protection Agency banned it in 1972. However, other countries still use DDT for mosquito control.

Sterilization

• Combined with malathion and pheromone traps, releasing sterilized male boll weevils into the general population reduces the chances of fertile eggs being laid. Male boll weevils receive sterilization in a laboratory. All boll weevil pupae, the stage before breeding adulthood, receive nine doses of gamma radiation over a three-day period. Those males that survive the treatments and reach adulthood are sterile or nearly sterile. Females can also be sterilized, but at much higher radiation levels, which usually kills most of the pupae.