Concepts of IPM and Biological Control

Biological Control may be defined (in as few words as possible) as: The use of living natural enemies to control pests. In slightly more words, it has been defined as: The active manipulation of antagonistic organisms to reduce pest population densities, either animal or plant, to noneconomically important levels.

Both definitions imply that biological control is an action taken by people using what are called "natural enemies" or "antagonistic organisms." These may be predators, parasites, parasitoids, pathogens, or competitors of the pest that is to be controlled.

There are various ways in which these "natural enemies" or "antagonistic organisms" can be put to work. The four major ways are by what has been called Augmentive Biological Control, Classical Biological Control (otherwise known as Inoculative Biological Control), Inundative Biological Control, and Manipulative Biological Control.

Augmentive Biological Control:

Release of large numbers of a biological control agent to supplement the small numbers already present, in expectation of a greatly increased effect.

Example: A stink bug is causing severe damage to lychee flowers and small fruit in an orchard. A beneficial wasp is naturally present but is killing only 10% of the stink bug eggs. Release of many more of the same wasp species, reared in an insectary, results in many more stink bug eggs being killed. The wasps reproduce and reduce damage to below the economic threshhold for the rest of the fruiting season. As an added bonus, use of these wasps, instead of a chemical pesticide, conserves honey bees which are pollinating the lychee flowers.

Classical Biological Control (Inoculative Biological Control):

Importation and release of biological control agents into an area in which they are not already present, with intent to establish a permanent population.

Example: USDA researchers import from South America a weevil that attacks an aquatic weed (also from South America). After determining that the weevil attacks only the aquatic weed, they breed the weevil in a laboratory and release a few hundred at many places in the southern USA. The weevil eats the weed and reproduces, and its populations grow and spread to still other places where the weed is causing problems. After a year or two, the weed and the weevil still exist at many places, but both at low numbers, and the weed is no longer a problem. Control is effectively permanent, with no need for future expenditures.

Seasonal Inoculative Biological Control is a subset of this and is defined as: Release of biological control agents in an area in which they cannot survive permanently due to severe climate or other constraints; the expectation is that they will establish a population that will persist for some fraction of a year.

Example A: Mexican bean beetle spread decades ago to the northeastern USA where it does severe damage. A wasp was found in India that attacks Mexican bean beetle and its close relatives (but the only close relatives in the USA are also pests). Unfortunately, the wasp cannot survive winters in the northeastern USA. So, small numbers of the wasp are maintained in an insectary and some of them are released at the beginning of each growing season in bean-growing areas. They attack the Mexican bean beetle, reproduce, control the numbers of the beetle throughout the growing season, and die in winter.

Example B: Seasonal inoculative releases of a South American flea beetle are used to control alligatorweed in more temperate areas where the plant has become invasive.

Inundative Biological Control:

Release of large numbers of a biological control agent relative to the numbers of a target species, in expectation of a rapid effect. There is no implication that the released biological control agent will establish a permanent population.

Example: A golf course is being damaged severely by white grubs (scarab larvae). The superintendent pays for an application of a biopesticide (in this case an entomopathogenic nematode that happens to be native). The nematode kills 90% of the white grubs within 10 days and then disappears because it cannot reproduce in them. This biopesticide is applied much like a chemical pesticide, but it consists of living nematodes. This is good enough in the eyes of the superintendent because white grubs will not reappear until next year. An added bonus is that the nematode is exempt from regulation by the EPA, the golf course does not have to be closed for play during and after the application, and the superintendent is seen as a good neighbor by residents of nearby homes (because they don't like use of chemical pesticides anywhere near them).

Manipulative Biological Control:

The manipulation of elements in the environment to enhance the numbers and/or actions of natural enemies.

Example: Channels are dug in a saltmarsh to connect pools of water. This allows naturally-occurring predatory fish to gain access to pools and eat mosquito larvae.

Conservation Biological Control is a subset of this because it seeks merely to conserve.

Example: Plots of a particular weed are left untreated with herbicide around a sugarcane field; these plants are a very important source of nectar for adults of a species of wasp that attacks white grubs (scarab larvae) that damage sugarcane roots. This conserves the wasp population, reduces the pest (scarab) population, and reduces damage to the sugarcane.

For further definitions, see the Glossaries