Biological Pest Control

The definition of biological pest control

The definition of biological pest control is the use of methods for controlling the population of a pest species using another organism. There are generally considered to be three different types of biological pest control- augmentation, conservation, and importation.

Augmentation

In augmentation pest control, a native species that is a natural enemy (a predator or parasite, for example) of the pest species is released into the ecosystem in significantly increased numbers in an effort to reduce the population of the pest species.

Conservation

Pest control through conservation is very similar to augmentation. Instead of releasing a native enemy species, it involves the conservation of the native enemy species in an effort to boost its population size.

Importation

Also known as classical biological pest control, importation involves releasing a non-native enemy of a pest species into an ecosystem in an effort to control the pest species' numbers. Although this has proven successful at times, it can be potentially problematic, as the introduced species may become an invasive pest species.

Methods of biological pest control

There are generally considered to be four methods of biological pest control: predation, parasitoidism, competition, and pathogen introduction.

Fig. 1: An ichneumon wasp, a parasitoid species often used for predation, one of the biological pest control methods.

Predation

The predators of a pest species may be augmented, conserved or imported to lower the population of the pest species to a more manageable level. However, it is unlikely to be eradicated. Predation can be an attractive pest control option when it involves native predator species, but significant negative impacts can arise if a non-native predator species is introduced (Fig. 1).

Parasitoidism

A parasitoid species can be used to lower the population size of the pest species that host their larvae.

Competition

Another method of biological pest control involves the introduction of a competitor species into the ecosystem. This results in interspecific competition, thus reducing the fitness of the pest species.

The introduction of pathogens

Pathogens are agents that cause disease in living organisms. These agents may be living (bacteria and fungi) or non-living (viruses). Pathogens can be very effective forms of pest control since they are an example of a density-dependent limiting factor and will generally increase in frequency as a pest population's size increases.

Benefits of biological pest control

There are many benefits to biological pest control. If carefully implemented, it can be environmentally safe and sustainable. It is also usually much more cost-effective than other methods of pest control.

- Extensive preplanning and research can ensure that the biological agent will only affect the target organism. In addition, these biological agents are free-living and self-sustaining, thus requiring minimal management.

- Biological pest control is also likely to have little or no impact on human health, in contrast to some chemical forms of pest control, such as pesticides.

- It is less probable that pest organisms will develop resistance to predators, competitors, or parasitoids, while they can build up resistance to certain chemicals (as well as pathogenic biological pest control agents).

Challenges of the biological method of pest control

There are many challenges posed by biological pest control, mainly if it is not carefully implemented. Introducing non-native organisms can have unexpected negative impacts on non-target species and the environment.

• If the non-native organism is a predator, it may prey upon many non-target species, sometimes to an even greater degree than the target species.

In addition to damaging non-target populations, this can be counterproductive to the goal, as it may result in the decline of competitor populations and the proliferation of the pest species.

Biological pest control can also be a prolonged and gradual process since it relies on predation, competition, and disease spread, rather than quick eradication. For this reason, biological pest control is not recommended for pest eradication but rather for pest management.

Examples of biological pest control

Varying methods of pest control have been used for many years as a way to maintain or even eradicate certain pests. Sometimes these control methods are successful, and other times they prove to be more damaging! Let's take a look at a few examples of both.

Fig. 3: An alfalfa weevil, an introduced pest species of alfalfa crops in the United States.

Negative examples

Cane toads (Rhinella marina) are a species of very large, terrestrial toads native to Central and South America.

Fig. 2: A cane toad, native to Central and South America, but a major invasive species in Australia. It was introduced there for predation, one of the methods of biological pest control.

In 1935, as an example of importation biological pest control, cane toads were introduced to Australia to control the populations of two pest beetle species that were decimating crops. Unfortunately, this resulted in an unprecedented ecological disaster, as the cane toads had no significant impact on the beetle population and became an even more catastrophic pest species.

Since the ingestion of cane toads proved fatal for most potential predators, many Australian predators' populations plummeted, and the cane toad population grew exponentially, reaching roughly 200 million.

In an effort to combat the cane toad expansion through augmentation, large numbers of keelbacks were released into wetlands and other areas severely affected by the toads. Sadly, this attempt does not appear to have significantly impacted the toad population.

Positive example

The European alfalfa weevil (Hypera postica) was introduced to the United States during the early 20th Century and had become an important pest of alfalfa crops by the 1970s.

• Two species of parasitoid ichneumon wasp (Bathylplectes anurus and B. curculionis) were introduced to combat this pest.

  Of the two species, it was found that B. curculionis was the most effective.

• In addition, a pathogen in the form of a fungus (Zoophthora phytonomi) was introduced because it was found to be fatal to the weevil's larvae.

Combining these two forms of biological pest control has made the weevil population manageable with negligible impact on the crops, non-target species, and the surrounding environment.