Noxious Weeds / Control Strategies / Biological Control

Idaho’s Biological Control Program

The Idaho State Department of Agriculture, Bureau of Land Management, and University of Idaho have joined together in the fight against noxious weeds.

This program provides state-wide technical advice, guidance, and training on integrated weed management (IWM), specifically targeting biological control of noxious weeds.

Biocontrol agents and activities in Idaho

What is Biological Control?

There are many definitions attributed to biological control. For our purposes, we will define the biological control of weeds as the use of live natural enemies (e.g. insects, pathogens, nematodes, mites) of pests to reduce plant pest population levels below that which would occur in the absence of the natural enemies.

There are commonly three types of biological control recognized:

• Classical – initially small numbers of natural enemies are released in target pest areas for long-term control.

• Augmentative – large numbers of natural enemies are released to control a target pest for a short amount of time.

• Conservation – changing environmental conditions to aid in natural enemy survival.

How is it used?

For over 100 years, biological control principles have been used throughout the world as an effective, economical, and environmentally responsible way to decrease the damage caused by invasive species. Biological control agents are ideally employed for use against established weeds rather than new invaders. The effectiveness of biological control can range from highly effective, where people may use this approach and exclude other weed control measures, to failure. Most biological control systems fall somewhere between the two extremes outlined above. Where this is the case, an Integrated Weed Management (IWM) approach should be used to control the weed species of concern, with biological control as a component of the strategy (where applicable), but not the sole solution.

Biological control and the general principles of ecology mesh well together by reuniting a target pest with its natural enemy. Ecological theory can assist biological control practitioners to better predict and monitor the target invasive species and the potential effectiveness and possible risks of the biological control agents. By dividing complex ecological processes into manageable, measurable stages, it is possible to identify failures in a biological control system. This adaptive management approach will guard against repeat failures and improve the effectiveness and safety of future programs.

How are Biological COntrol Agents Selected?

Biological control organisms are chosen from a large suite of natural enemies in the target plant’s native range. Foreign exploration for biological control agents is the first step in a new biological control program. Typically, scientists, land managers, and cooperators in the target plant’s native and introduced range are assembled to conduct the exploration. This process may take several years, although it is common to identify the first biological control agent candidate within the first year of exploration.

Once candidates are identified, each candidate species undergoes quarantine testing overseas and/or at a U.S. quarantine laboratory. This is an expensive process (approximately $250,000 per year) requiring several years of funding to accomplish. In addition to the monetary cost and the time investment, there are several other hurdles a potential agent must be subjected to before it can be approved for release in the United States.

After agents have been identified, they are tested for specificity using test plant lists developed by experts. Oviposition (egg laying) tests and feeding tests are used to determine the suitability of the test plants for successful development from egg to adult for potential biological control agents. These tests can be no-choice tests, where the insect is forced to feed on the test plant or starve, or multiple-choice tests, where insects are offered a choice among several potential host plants. The data generated from these tests (which typically take 2-3 years to complete) is then submitted by the biological control agent petitioner to the Technical Advisory Group (TAG) for review.

The TAG for biological control of weeds was established in 1987 and is made up of 15 governmental agencies representing the United States, Mexico, and Canada. Once the petition is submitted, the TAG members review it and can recommend an agent’s release which prompts the petitioner to submit a permit application to the Animal & Plant Health Inspection Service (APHIS) Plant Protection and Quarantine (PPQ), who then prepares an Environmental Assessment (EA). If the EA reaches a “finding of no significant impact” (FONSI), APHIS-PPQ then issues a permit. There are several “checks” in this process that have the potential to slow down the application for the new agent(s). This agent review process ensures that only host-specific agents will be released, dramatically decreasing the inherent risks associated with releasing a biological control agent into a new area.