Introduction

Invasive Species Defined

What's Being Done

 National Invasive Species Information Center

Submodule 4: Invasive Insects

General Characteristics

Most researchers agree that the most important indicator of success of insect infestations is that invaders are dispersed in a desirable habitat. In addition, data has shown that insects from large continents more easily invade island habitats than the other way around; this bodes poorly for a state like Hawaii, which certainly has its share of detrimental invasive insects. It is also not uncommon to have introductions of insects form one part of a region to another, such as introductions of insects from Canada to the U.S.

As with invasive plants, disturbed areas seem to be more readily invaded by non-native insects. This may be attributed to the fact that predators and competitors have also been disrupted in these environments.

An insect that has been introduced and established in a new habitat does not necessarily fulfill the definition of an “invasive species”. Not all introduced insects cause damage to their new environment. In fact, many insects have been intentionally introduced into new habitats to serve as biological controls for invasive plants, and some of these introductions have been quite successful in controlling the invading plant populations. Since one of the many reasons that invasive plants are successful in a new environment is freedom from their natural predators, it is logical that introducing an insect could help control the plant. One example of this is leafy spurge, an invasive plant that has devastated many areas of the northern U.S. Several nonindigenous species of insects have been approved for release in the U.S. to assist in the control of leafy spurge. These insects attack leafy spurge by several methods such as eating its vegetative growth or damaging its seeds.

Some invasive insects are able to pass diseases from plant to plant by transmitting bacteria or other infectious organisms. An example of this is the glassy-winged sharpshooter (Homalodisca coagulata), a bug that has been increasingly destructive in the grape-growing areas of California. Not only does this insect consume tremendous amounts of fluids from its host plant, it also frequently passes on a bacterium, called Xylella fastidiosa. Once this bacterium enters the grape plant, it clogs the plants water and nutrient transport system which eventually leads to leaf loss and death. Interestingly, the glassy-winged sharpshooter, native to the southeastern U.S., is now considered an invasive species in other parts of the county and is causing destruction in a new habitat in California.