What is Biological Control?

Biological control is the intentional manipulation of natural enemies by humans for the purpose of controlling pests. Biological control of aquatic weeds is especially attractive because rivers and lakes are sensitive ecosystems important to wildlife and human health.

There are three approaches to biological control: Conservation, augmentation and importation of natural enemy populations.

  • Conservation is the preservation and maintenance of the natural enemies that occur in an area.   Reducing insecticide use and providing flowers as nectar sources for wasps that need this food are examples of the conservation method of biological control.
  • Augmentation is the periodic release of natural enemies that do not naturally occur in sufficient numbers to provide pest control. Augmentative releases may be designed to “seed” natural enemy population or as inundatory releases that overwhelm pest populations. In Texas, because the problems are exotic species importation of host-specific enemies has been necessary for the success of biological control of aquatic weeds.
  • Importation of natural enemies into areas where they do not occur is sometimes called classical biological control and is the method most commonly used in biological control of aquatic weeds. Natural enemies from the native range of the pest are identified, collected, imported, reared and released. If successful the natural enemy will establish permanent populations and provide control of the pest without the need for further releases. Classical biological control includes several key steps: overseas research, quarantine research, release, establishment and technology transfer. Relatively few biological control agents that are initially considered actually make it to the release stage. Even fewer of those released successfully establish and control the weed.

Biological control is most effective when used together with other compatible pest control practices in an integrated pest management program. Many control programs use a combination of techniques to deliver rapid control yet provide a longer-lasting cost effective control program. Mechanical control or herbicide control programs for aquatic weed can be combined with biological control to provide such a program. When combining techniques it is a good practice to maintain an otherwise uncontrolled area of plants for the insects to use as a nursery to establish and build up.

What are the alternatives to biological control of weeds?

There are three main methods used for control of weeds: biological, mechanical, and chemical. Mechanical control includes mowing, hoeing, cultivation, and hand pulling. Chemical control is the use of herbicides. You can also use a combination of these three methods in an integrated weed management approach which some authorities would consider as the fourth method.

What are the advantages of biological control?

The advantages of biological control are

  • It is inexpensive
  • It poses little threat to non-target organisms
  • Once established, biological control agents are self perpetuating and can spread on their own
  • Little additional effort is required once a biological control organism is established, while other control methods require action or inputs periodically
  • The environmental impact is generally low

What are the drawbacks to biological control?

The main drawbacks to biological control of weeds are:

  • There is always some risk and concern with introducing an exotic organism into the environment. The main concern is a host shift of a biological control agent that results in the agent feeding on a desirable plant.
  • Biological control agents are not available for all target pests. Some of the target weeds are closely related to plants that are desirable so the risk of introducing an agent is too great.
  • Research time and money is needed to locate biological agents and screen them for host range before the agents are released. It generally takes years of research and testing before agents are released.
  • Biological control takes place slowly in most cases. Localized weed problems may not be eliminated quickly enough to satisfy public opinion.
  • Biological control relies on populations of the weed and the agent to maintain the system.  Thus, weeds are not completely eliminated. Also, there is often highs and lows in population levels of the weed and the agent both in time and space. Thus, there are some situations where biological control does not seem to work well.

If there are advantages and disadvantages how is the decision to use biological control determined?

The decision is made on a case-by-case basis. The potential impact of the weed, the alternative control measures available, the risk to the environment, and the consequences of doing nothing are all considered. The scientific information and the social values all influence the decision. Once the organism is released, there may be little good alternative to reverse the decision, so this decision is taken seriously. This is further complicated by the fact that social values change through time and that the scientific information available will also change as new information becomes available. There a number of regulations in place that impact the release of organisms.

John Jackman, June 26, 1999

What is the Difference between “Laws” and “Regulations” Governing the Biological Control?

Law is the term used to denote what has been passed by the legislature and appears in the Texas Agricultural Code .  Regulation, on the other hand, is the law as interpreted by the administration, such as the state department.  Laws can be vague in language, but regulations are more to the point and specific.

Oct. 20, 1999.  Awinash Bhatkar, Ph. D., Texas Department of Agriculture

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