Biological control (biocontrol) is the selection and introduction of a natural enemy of an invasive plant or insect pest which suppresses that pest in its home range, and the “reuniting” of this natural enemy with the invasive pest to provide long-term, cost-effective, and sustainable pest management. Historically, the focus of introducing a biocontrol was solely pest reduction, with little or no focus on minimizing unintended consequences. However, changes in the 1970s prioritized the environmental safety of overarching frameworks for all biocontrol projects, which dramatically changed the protocols and regulations for selection, testing, release, and monitoring. Since then, the practice of biocontrol in Hawaiʻi and across the globe has been successfully used to manage some of the world’s worst pests.

Since 1975, more than 50 biocontrol species have passed through these protocols and regulations and have been released in Hawaiʻi to control invasive species, and there continues to be no environmental or non-target impacts to species other than their intended invasive pest target.

Biocontrol is just one of the many tools that are needed to reduce the impacts on our environment, agriculture, economy, and public health, caused by some types of widespread invasive species.

Biocontrol projects in Hawaiʻi are cooperative efforts between multiple agencies and organizations, including the Hawaiʻi Department of Land and Natural Resources Division of Forestry and Wildlife, Hawaiʻi Department of Agriculture, USDA Forest Service, University of Hawaiʻi, and international partners to plan, research, implement, and monitor projects.

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Infographic outlining the biological control release processWhy do we need it?

The Hawai’i State Legislature has defined invasive species as the “single greatest threat” to our economy, natural environment, and health of our communities. When invasive species arrive in Hawaiʻi, they almost never encounter the environmental conditions or species that kept their populations under control in their home range. Released from natural controls, some invasive plants and insect pests are beyond our ability and capacity to eradicate or even control by labor, pesticides, or other methods. Many of these invasive species are simply left to spread because there are no viable options. However, there are some invasive species that, if left unchecked, pose too high a cost (their continued spread would impact water supplies, endanger native plants or animals, or cause public harm, etc.). A successful biocontrol could reduce the future impacts of some types of invasive species, such as certain invasive plants and some types of insects and invertebrates.

Does introducing a biocontrol reduce invasive species impacts?

The practice of biocontrol relies on finding an invasive species’ natural enemy (sometimes called a “biocontrol agent”) that needs its invasive species “host” for food or shelter for part of all of its life. Reuniting a natural enemy with its host re-starts that natural process and can result in a decline in the “host” populations, or more often just impacts the overall health and growth of its invasive species hosts. Without its invasive species “host”, the natural enemy cannot continue to survive. Instead, the populations of each rise and fall in waves.

Advantages and positive effects of successful biocontrol

  • Cost-effective
  • Sustainable
  • History of success in Hawaiʻi and around the World
  • Long-term effects with little need for additional labor
  • Often reduces need for pesticides
  • Protects native Hawaiian ecosystems and forests for the purpose of conserving native flora and fauna
  • Preserves public water supply
  • Conserves lands for public use recreation and education
  • Protect culturally important resources

Mongoose were never a biocontrol project

People continue to point to the introduction of mongoose in 1883 as an example of what could go wrong. A sugar plantation owner’s ill-fated decision to import mongoose to control rat populations is not considered an example of classical biocontrol. It is, rather, a good example of the disregard for environmental concern and the absence of proper regulation that was prevalent until the 1970s.

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