Pros and Cons of Biological Control

Abstract

Biological control involves the deliberate introduction of natural enemies for the control of pest organisms, including insects, weeds and diseases.A general difference exists between augmentative releases where biological control agents are used periodically, i.e. once or several times within a season, and classical biological control where agents are released with the aim of establishment and, ideally, a permanent pest control.Whereas native candidates are generally given preference in augmentative biological control, in some cases exotic species have been used. By contrast, for classical biological control the rule is that exotic natural enemies are introduced for the control of exotic pests. Pest species may either interfere with agricultural production without being invasive per se or may be invasive on a larger scale, thereby threatening ecosystems and natural reserves. Whereas arthropod biological control generally applies to the former, it is in the weed control section that biological control agents are often released to control invasive species. This means that biological control finds itself in the unique position of being both an important strategy for the control of alien invasive species and also a route by which potentially damaging new alien species (i.e. the natural enemies) are themselves introduced and spread (Chap. 2). This chapter will briefly review the positive aspects of biological control and will highlight a few examples. It will further review negative aspects of biological control introductions. One of the examples where biological control led to detrimental environmental effects was the introduction of the ladybeetle Harmonia axyridis, and this case will be outlined in more detail. This example will also be used to explore some of the population biology mechanisms which can contribute to the net effects of introduced natural enemies. Finally, some information on recent developments and improvements in risk assessment of biological control agents is provided.