HISC eNews: Applying a Conservation Tool

"Applying a Conservation Tool"

HISC eNews

August 29, 2008

www.hawaiiinvasivespecies.org

Featured Update

In Hawai'i, several species of non-native ornamental Erythrina trees have been affected, including the native Erythrina sandwicensis. An African parasitic wasp will battle the Erythrina gall wasp whose damage can be seen here. Photo by Forest & Kim Starr.

Biocontrol is the importation of a natural enemy from the native habitat of a pest for the purpose of controlling the pest. This practice is based on the principle that specialized insects or diseases that keep a plant in balance in its native range can be used, after careful testing to check their safety, to help restore ecological balance in Hawai'i, without causing harm to other species.

The state is preparing to release three types of insects to help control harmful invasive species that have become established in Hawai'i.

An African parasitic wasp will battle the Erythrina gall wasp, which destroys native wiliwili trees.

A parastic wasp found in Taiwan will help control the nettle caterpillar, which is highly damaging to nursery plants, and packs a painful sting.

An African moth's larvae will eat Madagascar fireweed, a daisy-like flower that is toxic to cattle, horses and other livestock when ingested.

The U.S. Forest Service is also preparing to release a Brazilian scale insect to reduce strawberry guava's reproductive capacity, a threat to native forests and watersheds.

To determine host specificity of biocontrol agents, scientists put each potential biocontrol species through a rigorous process that includes a scientific literature review, biological studies at point of origin, choice/no-choice feeding tests in a quarantine facility on organisms related to host and unrelated species, including environmentally and economically important organisms. Each organism proposed for release must be reviewed by interested agencies and put through a permit and environmental assessment process by the USDA and HDOA Plant Quarantine Branch.

Typically, biocontrol species are co-evolved with the host organism and can only complete their lifecycle on the host or target species under consideration. As such, they are unlikely to completely kill a host plant, but they can make it less competitive. The introduction of a biocontrol species makes foreign species that arrived in Hawai'i without any natural co-evolved enemies behave like normal species in their native range. Under this modern vision of biocontrol, none of the species proposed for biocontrol will be generalist feeders capable of eating or damaging species other than the target species. Years of research may be required to determine if this is the case.

Advantages

Environmentally safer than chemicals, such as insecticides and pesticides
Cost effective
Natural solution
Sustainable, longterm solution

Disadvantages

Not effective for small infestations
Requires months to years of research
May require foreign exploration
Not a solution for every invasive species

Since 1975, 51 biocontrol species have been purposefully introduced to Hawai'i after thorough testing. According to the Hawai'i Department of Agriculture, none have resulted in the eradication of their host and none have become invasive in their own right. Biocontrol species introduced against invasive plants have been particularly specific to their targets and have successfully controlled the rampant spread of important weeds, such as lantana, prickly pear cactus, mistflower and banana poka.

Aloha

Gardening and yard work can be hard and laborious tasks. Just clearing the haole koa or guinea grass could take days of hot, ache-inducing pulling, cutting and hauling. And it all grows back. Imagine doing this over thousands of acres of public and private lands in remote, densely forested areas. To work there would mean hiking in with a heavy backpack, water, cutting tools, and probably a weed whacker and chainsaw. You would have just a taste of invasive species control.

Controlling invasive plants and insects cost farmers and ranchers millions of dollars in crop damage and loss of production. In forests and natural areas, field crews spend thousands of hours each year controlling invasive plants. Unfortunately, a number of invasive species have invaded and continue to spread through the Hawaiian landscape to a point that it is no longer feasible to manually control.

For example, control of the wiliwili gall wasp is considered impossible although great efforts are under way to protect a few individual wiliwili trees. Native wiliwili seeds were collected and safely stored in the hopes that a natural enemy of the gall wasp may be found so that these trees might thrive once again.

Since 1975, the search, testing and release of specific natural enemies (biocontrol) of invasive species have successfully reduced the invasive natures of several of our worst pests while remaining specific to their intended targets. By weakening an invasive species' vigor, biocontrol leverages the control efforts of farmers and field crews and, in many cases, allows native species a chance to compete.

Today, biocontrol is an accepted and mature conservation tool that is used worldwide. In this age of global commerce and unprecedented species movement, we need all the tools we can get to help protect Hawai'i from invasive species.