Biological Control Basics

Biological control is a great way to naturally control pests, and there are many different ways to implement it in a garden, both indoors and out. Biological control is a pest management tactic involving purposeful, natural enemy manipulation to obtain a reduction in pest populations.

More simply put, biological control means using good bugs to kill bad bugs. The most common example is releasing natural enemies that were purchased from a biological control company into a crop to control pests. Other examples include tactics to increase existing natural enemy populations that are already present, but not providing enough control.

We use the term natural enemies throughout this article, which is a general term used to describe living organisms found in nature that kill pests outright, weaken them or weaken their ability to reproduce. To use natural enemies for pest management and biological control, it is important to understand your pest, its natural enemy and the principles of biological control.

Biological control can be broken down into four categories: natural control, conservation biological control, inoculative biological control and inundative biological control. They are all different and can be combined to provide several layers of protection for the garden.

Natural Control of Pests in the Garden

Natural control is the logical place to start when talking about biological control because it is the type of control we see in our gardens already. Natural control keeps pests from becoming a problem, with no input from the gardener and refers to the normal ecological interactions, both in the wild and in cultivated crops, which keep pest populations at bay.

This includes interactions such as ladybugs eating aphids naturally in the garden. These interactions between natural enemies and their prey keep pests at low levels and allow plants to grow and reproduce naturally. However, pests can quickly outpace their natural enemies and overwhelm a managed crop.

This happens in nature, too, but generally on a smaller scale, and plants simply die or become less productive. Unfortunately, when a managed crop is the host of a pest infestation, pest management tactics are required. Helping out natural enemies is a good place to start.

Conservation Biological Control

Conservation biological control involves protecting and stimulating the performance of naturally occurring natural enemies. This is the most cost-effective, holistic approach to dealing with pests. A great way to do this is to plant banker plants. A banker plant is a non-crop plant grown amongst a crop where natural enemies can live before moving out onto the crop.

Banker plants are commonly used for aphid control in greenhouses, where barley is used as the banker plant and a special aphid that only feeds on grasses is grown on the barley. This special aphid—the bird cherry-oat aphid—grows in great numbers but will not move onto the crop plants.

A parasitoid called Aphidius colemani will come and attack these aphids and be present in the greenhouse even when there are no other aphids on the crop. These parasitoids target many species of aphids and are good at finding them. They will cruise through the greenhouse, protecting crops from incoming aphids. If they can’t find anything, they will go back to the banker plants and parasitize the non-pest aphids.

Other methods that fall into the conservation biological control category include inter-cropping, planting hedgerows and providing supplementary food. All of these help increase the population of natural enemies in the crop and provide pest control.

Inoculative Biological Control of Pests in the Garden

Inoculative biological control is the next step in the biological control spectrum and is generally used on invasive pests in the landscape. Natural enemies are collected from where the pest originated, and released where the pest was accidentally introduced. The goal is to build up the numbers of the natural enemy over time and suppress pest populations with no further inputs.

This tactic has been used successfully to control several invasive weeds and insects in the United States for decades. It was first used in the late 1800s in California to control cottony-cushion scale, a devastating citrus pest. A predatory beetle and a parasitoid wasp from Australia were introduced, and to this day provide effective control of cottony-cushion scale in California. Because inoculative biological control was the first biological control method used in modern agriculture, it is sometimes referred to as classical biological control.

Inundative Biological Control of Pests in the Garden

The last type of biological control is inundative biological control. Using this method, natural enemies are mass-reared in insectaries for release in large numbers to obtain an immediate control of pests. This method can be thought of as biological insecticide because the intention is to overwhelm the pest population with massive numbers of natural enemies. In many cases, if the environmental conditions are correct, the natural enemies become fully established, providing ongoing control.

The inundative method is highly effective in contained growing environments because high densities of natural enemies can be maintained, and dispersal onto the crops is limited. There are many insectaries around the world that produce an amazing assortment of natural enemies to control a range of pests, including aphids, spider mites, fungus gnats, thrips and houseflies.

Biological control is a complex pest control system that relies on manipulating natural ecological interactions to control pests.

The principles we have highlighted can be used to craft a pest control plan and keep crops at the correct ecological balance for peak production. Keeping natural enemies in mind when designing a cropping system will help prevent pest problems and lead to a more harmonious crop.

Biological control is an ecologically friendly way to control pests in a garden and is a great way to reduce the use of pesticides. A great resource to help you identify pests and provide ideas for biological control options is the University of California’s Integrated Pest Management website.

Co-authored by Bob Starnes.