The idea behind biological control is to recruit soldier organisms to wage war against other undesirable organisms. Many organisms may be employed to fight the battle; among them are these easily accessible and popular organisms: Bacillus thuringensis, Bacillus popillae, pheromones, and hormones.
Bacillus thuringensis (BT) is a bacterium utilized to attack many caterpillars, which also include corn borers, gypsy moths, canker worms, tomato hornworms, and tent caterpillars. The bacterium is sprayed on plants infested with the invading pest. The insect eats the bacterium along with its normal food. Then the bacterium does its work by causing sickness with the death of the pest following rapidly behind. BT is effective in eliminating large populations of caterpillars and should only be used when the population is out of control because BT will also kill off the caterpillars that turn into butterflies and beautify the garden.
Bacillus popillae is a bacterium that only kills the grub of the June beetle and does not harm beneficial insect species.
Pheromones are secretions of animals and the scents on insects. The pheromones signal the location of food, dangerous conditions, or mating conditions. For the purposes of biological control, pheromones are used to confuse pests so that they become incapable of reproducing or to lead the harmful insects away from a crop. The pheromones are synthesized from chemicals to imitate naturally occurring pheromones in insects. The pheromones should not be placed on the host plants because this will only lure the harmful insects toward the crop. Instead, the pheromones should be placed as far away from the crop as feasible to dispose of the harmful insects.
Hormones are chemicals within the body of insects that play a part in regulating growth. Hormones can therefore be used to the disadvantage of the insects by keeping the insect at an immature stage. Being unable to reproduce will quickly end the insect invasion.
Another popular way to destroy pests selectively, without killing beneficial insects, is to use predator insects. The Australian lady beetle helped to destroy cottony cushion scale for citrus growers. The introduction of the fly, Lydella thompsoni Herting, and the wasp, Macrocentrus grandii Goidanich, helps to control the European corn borer. The tachinid fly, Cyzenis albicans, and the ichneumon wasp, Agrypon flaveolatum, attack the winter moth in Canada. In a greenhouse study at Central Texas College, lacewing and ladybird beetles were used in an attempt to destroy the population of whitefly as well as other destructive insect pests. However, as is often is the case, biological control, pales in comparison to the speed and effectiveness of chemical controls.
In the long-term, biological control is very economically efficient, and once implemented and maintained it can produce very promising results. Patience is a desirable quality to have when managing pest problems as some control measures may work in opposition to each other such as with predacious insects and broad-range, organic insecticides if not implemented in a manner that would be symbiotic with the surroundings. One may not know whether the insects have stopped to feed, nest, reproduce, rest, play, or leave waste. Nevertheless, it is desirable to study pests with as much detail as can be obtained in order to have the best information to decide the best method to managing the pest population.
The third approach to biologically controlling insect pests is to use the plants themselves, ally plants, or sacrificial plants. There are more than twelve varieties of wheat that are resistant to the Hessian fly. Problems with spotted alfalfa aphid have been eliminated since 1954 because of the breeding of resistant varieties of alfalfa. There are also some varieties resistant to insects and mites, which include the following: barley, beans, cotton, grasses, onions, peanuts, peppers, tobacco, potatoes, sugarcane, rice, sorghum, soybeans, and tomatoes. Marigolds are used as ally plants in many home gardens to avert a number of insects. A crop of small acreage can be sacrificed to the harmful insects to save the main crop.
In closing, biological control of insect pests can be a long, on-going maintenance program requiring much time, insight, and foresight. Nevertheless, the rewards will make it all worthwhile.