Biological control as it relates to horticulture and agriculture is the use of parasites, pathogens and predators to control pest populations and damage. These biological agents are known as natural enemies. The benefits offered by these biological agents is supported via conservation, augmentation and classical biological control tactics. Most parasites, pathogens and predators are highly specialized which make them ideal for targeted past management.
(see: Natural Enemies Handbook and the Natural Enemies Gallery)
A parasite is an organism that lives and feeds on a host. In this instance, these parasites are called parasitoids because they kill their hosts. Parasites that infect insects can develop in or outside a host’s body. Typically, only immature parasites (larvae) feed on hosts. However, there are instances where the adult females of parasites feed and kill their hosts (ex. wasps that attack whiteflies and scales). This makes parasitoids excellent for biological control.
Most parasitic insects are flies (Diptera) or wasps (Hymenoptera).
A pathogen is a microorganism. These microorganisms can infect and kill their hosts. There are natural enemies like certain bacteria, fungi, nematodes and viruses which can greatly reduce the populations of pests, such as aphids, caterpillars, mites and other invertebrates. This often takes place under naturally occurring conditions (epizootic) like prolonged periods of high humidity and/or dense pest populations. Pathogens can also be commercially purchased in the form of biological or microbial pesticides. Some of the most commonly used pathogens for biological control include Bacillus thuringiensis (Bt), entomopathogenic nematodes and granulosis viruses.
Predators are organisms that kill and feed on prey. Examples include predatory beetles, flies, lacewings, true bugs (Hemiptera) and wasps. Spiders are also included in this category, as well as predatory mites.
There is also classical biological control (importation) which is typically only used against exotic pests that have been introduced to a given area by mistake. This is necessary due to the fact that many organisms that are not pests in their native habitat become pests as a result of a lack of natural controls in a new environment. Before importation, the pest’s habitat is studied and natural enemies are identified. The theorized control agents (natural control agents) are then collected and their use is tested in a controlled environment for efficacy before widespread action is taken. This method is quite effective if proper control efforts are taken. To ensure maximum effectiveness and reduce the probability of negative environmental impact, importation is only completed by qualified scientists with proper permits in a controlled manner.
The long-term benefits of importation and other biological control efforts are dependent on cooperation with and support from the public, as well as landscape managers.
The safety of biological control has been questioned due especially in instances where exotic species are introduced to address problems with non-native/invasive species. However, when proper procedure is taken and control measures are used, biological control is considered safe for human health and the environment – especially in comparison to the widespread application of chemical control agents. Furthermore, the negative impact of biological agents is often much less significant than the negative impact of an invasive species.
To mitigate the environmental risk, biological control methods should only be used when proper research and management efforts have been made.