Abstract
Classical biological control (CBC) is the introduction of a natural enemy of exotic origin to control a pest, usually also exotic, aiming at permanent control of the pest. CBC has been carried out widely over a variety of target organisms, but most commonly against insects, using parasitoids and predators and, occasionally, pathogens. Until 2010, 6158 introductions of parasitoids and predators were made against 588 insect pests, leading to the control of 172 pests. About 55% of these introductions were made against pests of woody plants. Establishment rates of natural enemies and success rates were higher in CBC projects targeting pests of woody plants than other pests. This review aims to answer the questions most commonly asked regarding CBC against insect pests, with particular emphasis on tree pests. The topics covered include, among others: variations in rates of successes among different systems, different target insect groups and different agents; temporal trends in CBC practices and successes; economic and environmental benefits; risks and ways to mitigate the risks; CBC against native pests; accidental successes through the adoption of the invasive pests by native natural enemies or accidentally introduced agents; and prospects and constraints for the practice of CBC in the future. Questions are answered based on the analysis of two databases, the BIOCAT2010 database of introductions of insect biological control agents for the CBC of insect pests, and a database of introductions of entomopathogens against insect pests.
Highlights
Classical biological control (CBC) is defined as the introduction of a natural enemy of exotic origin to control a pest, usually exotic, aiming at permanent control of the pest (Hajek 2004; Van Driesche et al 2008)
Invasive insects are more likely to be adopted by native natural enemies if (1) the exotic insect belongs to a group of insects that are usually attacked by polyphagous natural enemies and (2) there are, in the region of introduction, insects that are taxonomically and ecologically closely related to the invader
Until 2010, 6175 introductions of insect CBC agents were made against 588 insect pests. 33% of these introductions led to establishment and 10% resulted in satisfactory control against 29% of the pests being targeted
Summary
Classical biological control (CBC) is defined as the introduction of a natural enemy of exotic origin to control a pest, usually exotic, aiming at permanent control of the pest (Hajek 2004; Van Driesche et al 2008). The objective of this review is to answer the most common questions that are posed by the public and scientists to CBC practitioners It will focus on the use of exotic arthropods (parasitoids and predators) and pathogens to control insect pests, i.e. other targets such as other invertebrates, vertebrates, weeds and pathogens will not be covered. Cock et al (2016) provided a description of the database and an overview of trends in the use of insects for the CBC of insect pests, but did not attempt any analysis based on the target crop type For this analysis, the database was expanded with 17 additional records from the older forestry literature which had been overlooked in the original compilation of BIOCAT (Greathead and Greathead 1992). This information is largely based on establishment rates as numbers of introductions were considered too low to generalize about successes, there have been some very successful programs
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