Revised 97 FEB18
Biological Control of Pests
By Harold Eddleman, Ph.D., President, Indiana Biolab
Pest control methods have changed greatly in the last 25 years. Toxic metal sprays, such as arsenic, have been replaced by organic compounds which do not survive long in the soil. Humans have observed insects eating other insects for thousands of years. Entomologists, scientists who study insects, have studied and reported such insects for a few hundred years. Occasionally, ladybird beetles, praying mantis, and other insects were collected and placed on crops where they could eat insects damaging the crop. In recent decades, great efforts have been made to improve natural controls. Often the old arsenic insecticides did not affect beneficial insects greatly because insects like ladybugs do not eat the poisoned leaves. However, many of the organic insecticides act without being eaten and often populations of mites multiplied profusely when the insecticides killed their enemies but did not harm the mites.
Integrated pest management (IPM) is becoming popular among gardeners and farmers. Enterprising young entomologists have developed businesses of aiding interested farmers by visiting the farms regularly, usually weekly, and determining the number and species of pests causing damae. When they find enough pests, the farmer may spray or release enemies of the pests. By measuring humidity and temperature farmers can also apply sprays or natural controls at the best time, often reducing the number of applications needed per year.
Study of biological controls of pests is a safe interesting project for youngsters, gardeners, farmers, and hobbists. We will suggest projects on this page. For example, if you live in an area where the tomato or tobacco hornworms are pests, you have probably seen some of the 2-inch "worms" covered with the white cocoons of the tiny wasps that have been growing inside the caterpillar. Such caterpillars are unable to eat or complete development; they are "dead". If you take such a caterpillar and place in a cage you will find tiny wasps (no sting) emerging from the cocoons. Examine the wasps, and then release them. If you examine hornworms in the field, it is not difficult to find mature wasp larvae (white grubs) eating holes along the dorsal line to emerge from the hornworm. A little later you can see them rearing up high to spin a cocoon on the back of the hornworm. There is no need to be afraid of tobacco hornworms they are harmless and can not sting. A low power (3 to 10X) microscope or handlens will aid such studies. You can see them by naked eye. After you learn what the wasps look like, you will be surprised how often you find them indoors and outdoors. A glass jar with a lid of fine cloth held in place by a rubber band or canning ring makes an ideal cage for holding and rearing insects. Nylon stocking makes a good cover for the jar.
If you collect and rear insect larvae by feeding them leaves from the same plant on which you found them, you will usually learn what type of adult they become. You will find many of the caterpillars fail to become adults because they already were hosts of tiny wasp grubs when you collected them. There are dozens of species of such tiny beneficial wasps. Using nylon stocking to cover the jar will admit plenty of air to reduce disease problems and prevent tiny parasitoids from escaping. Frequently, insects you attempt to rear will die due to diseases such as baculoviruses. The stress of living in a jar seems to help the disease win against the insect's defenses. Some say if you grind such diseased insects in water and spray the infusion on plants you will spread the disease and control that insect species.
Road-killed animals are very smelly to work with, but if you work outdoors, you will find tiny wasps emerging from the fly pupae that develop from the maggots. Does the smell attract the female wasps? Female wasps of some species insert the egg inside the pupa, but sometimes larvae I collected produced wasps in pupa stage suggesting some wasps insert their eggs into larva. Examine the wasps carefully and you will find more than one species in my region.You can distinguish the species by naked eye. The wasp grubs of one species leave the insides of the fly puparium dry, but the grubs of another species of wasp produce a sticky, slimy mess inside the puparium. Can the grubs of both species of wasp mature inside the same puparium? I believe I have gotten both species of adult wasps from the same fly puparium. If you try working with meat or roadkill, be sure to provide sand (3 or more cm deep, damp, not wet) in the gallon jar for the fly maggots to enter for pupation. In nature, fly maggots enter the soil to pupate. I use 1/2 inch hardware cloth as a lid to keep cats out and allow free passage of flies.
While you are waiting for me to add to this page, you will want to visit a Cornell University site which offers photographs and descriptions of important pests and natural control agents. Life cycles, habits, factors affecting biological control, and commercial sources are given. If you know of other web sites related to bio-control, please send me an e-mail.
A SPELLING LESSON. Which of these is spelled correctly: sweetpotato, Irish potato, cloverworm? All of them. Irish potato is a potato so the adjective is separated from the noun. Sweet potato is not a potato so sweet is not an adjective. Same for cloverworm; it is a caterpillar not a worm. Cloverworm and clover caterpillar are both correct, but clovercaterpillar is wrong..Most people write earthworm, but they are true worms and should be spelled earth worm!