Benefits and Failure of Imported Animals in the Fight Against Pests

Abstract

The employment of living organisms in the fight against pests is called biological control. The target organisms are completely eradicated, but should be suppressed at a tolerable level. As agents for biological control predators, parasitoids and pathogens are used. Different vertebrates (fox, toads etc.) and a number of free-living insects (ladybeetles, lacewings etc.) serve as predators. Parasitoids used were found within the insect orders Hymenoptera (Trichogramma, Apantheles etc.) and Diptera (Compsilura, Cryptochaetum etc.). Pathogens employed belong to bacteria (Bacillus thuringiensis strains) (Miller and Wansbrough 2002) and to the group of viruses (myxomatosis virus, rabbit calicivirus). Agents such as the entomopathogenic nematodes Steinernema and Heterorhabditis, which are assembled for the control of arthropod pests – for instance against weevils like Otiorhynchus sulcatus – act as parasites (the nematodes) and pathogens (symbiontic bacteria such as Xenorhabdus and Photorhabdus). The present chapter describes the tactic of the invaders and the problems that they pose inside their new environment for other domestic species but also for humans. To understand how important such invaders may be can be calculated from the fact, that in Germany about 1,500 new species arrived during the last 20 years (800 plant species, 700 animal species) or by the fact that the import of only 60,000 little Aga toads into Australia led to a population of 200 million specimens – today.