Brent Cornell

    
Controlling the population of invasive species once they have become established is difficult and typically very expensive

• There are three main methods of population control – physical, chemical and biological

Physical Control

Physical control involves the removal or restriction of invasive species by manual or mechanical measures

• This may include the installation of barriers and fences or the removal of habitat by excavation or trimming
• Population numbers may be reduced by hunting, trapping and culling, although these methods are labour intensive
• Physical methods to contain invasive species are not usually species specific and can also impede endemic wildlife

Chemical Control

Chemical control involves the use of chemical agents (poisons and toxins) to limit population numbers and spread

• Chemical agents may include herbicides (for plants), pesticides (for insects) or other compounds (e.g. rat poison)
• Chemical agents may have moderate specificity, but can also detrimentally affect local wildlife and are costly to employ
• The effect of chemical agents may become more pronounced in higher trophic levels due to biomagnification

Biological Control

Biological control involves using a living organism (or a virus) to control an invasive species

• The biological control may eat the invasive species (predation) or cause it to become diseased
• Biological agents must be carefully assessed before release to ensure they do not become invasive themselves
• Examples of agents include the Vedalia beetle (feeds on citrus plant invertebrates) and the myxoma virus (infects rabbits)
• Biological control agents must be monitored for unintended side effects (e.g. development of immunity in invasive species)

Biocontrol Case Study:  Vedalia Beetle

The cottony cushion scale is an invertebrate pest from Australia that was accidentally released in California

• It spread and fed on citrus plants (e.g. orange trees) to such an extent that it devastated the Californian citrus industry

The vedalia beetle is a predatory insect from Australia that was introduced into California as a means of biological control

• It worked to limit the numbers of the cottony cushion scale and minimise the economic impact to the citrus industry

Vedalia Beetle and Cottony Cushion Scale