Insecticides are in common use in agriculture as well as in houseplant populations, gardens, and other living spaces in an attempt to control the invasion of a seemingly endless array of insects. Using insecticides does work to keep populations under control, but over time insects can build up a resistance to the chemicals used. This is called insecticide resistance. Insecticide resistance is apparent when a population stops responding or does not respond as well to applications of insecticides.
Often insects will develop genetic changes that allow them to withstand the insecticide applications. Anytime an insecticide is used, it is unlikely that all the members of the population will be wiped out. Those in the population that develop a heritable change can pass it on to future generations in gradually increasing numbers. As each generation produces more individuals that are resistant to the chemicals, the overall effectiveness of the applications can be seen to diminish. Insect populations that reproduce quickly can show resistance in a short period of time.
DDT, developed in the early 1940s, worked to eradicate most pests, but in the late 1940s, insect populations were already beginning to show singes of developing insecticide resistance. According to the Insecticide Resistance Action Committee (IRAC), populations have developed signs of resistance to all the new classes of insecticides, including formamidines, cyclodienes, carbamates, pyrethroids, and organophosphates.
In confined spaces such as greenhouses, insecticide resistance is usually limited to one area and does not alter the genetics of surrounding insect populations. But flying insects and populations that demonstrate migratory behavior make the spread of altered genetic material a likely reality. This forces chemical companies to continue to develop new pesticides that the insect populations are not yet resistant to in order to control pest in crops and garden areas.
A simpler way insect populations develop resistance to a pesticide is by developing behavior that allows them to avoid the poison. Some insects will move away from the affected area and hide in untreated foliage or near the center of the plant where the insecticide was not thoroughly applied. Some flying insects will simply leave a treated area and return when the insecticide has worn off.
There are a variety of ways to avoid insecticide resistance. Different insecticides should be used in a rotation so that the populations do not develop resistance to anyone chemical. Other methods of insect control, such as the use of insecticidal oils and soaps, may be less likely to result in insect resistance.