Multiple agents in biological control: improving the odds?

Abstract

The current interest in risks associated with classical biological control led us to review the literature to determine whether the introduction of multiple biological control agents has been more effective than the introduction of a single control agent. We analyzed 59 projects against weeds and 108 projects against insect pests. Establishment of control agents was significantly higher in single-agent projects than in multiple-agent projects against insect pests, but not in projects against weeds. The success of biological control against weeds increased with the number of agents released. However, no relationship was found between the number of agents released and biological control success for insect pests. These results suggest that negative interactions may play a significant role amongst biological control agents of insects. Thus, multiple releases may be effective against weeds only. In over 50% of the successful multiple-agent projects against weeds and insect pests, a single agent was shown to be responsible for success. This result indicates that, in a majority of biological control projects, multiple agents are not released for a cumulative control effect but to increase the likelihood that the right control species is released (lottery model). Considering the possibility of negative interactions among biological control agents and taking into account the risks associated with natural enemy introductions, we recommend restraint in the introduction of multiple agents for biological control.

Response of Pale Swallow-wort, <em>Vincetoxicum rossicum</em>, following Aboveground Tissue Loss: Implications for the Timing of Mechanical Control

“…However, the ability of the plant to regrow following aboveground tissue loss both underscores the need for a more sustainable means of controlling this invasive weed, such as biological control, and argues against introducing a leaf-chewing herbivore as the sole control agent. Adequate control of target plants following the introduction of a single herbivore is the exception rather than the rule (Julien 1989) and success is often achieved only after introduction of several herbivores (Denoth et al 2002) that damage the plant in complementary ways (James et al 1992). Damaging the target plant in complementary ways can also be achieved through integrated weed management, for example, by combining mechanical control with biological control (Paynter and Flanagan 2004).…”

Pest species diversity enhances control of spider mites and whiteflies by a generalist phytoseiid predator

“…Much research has been devoted as to whether the presence of multiple natural enemies leads to more efficient pest suppression than the presence of single enemy species (Rosenheim et al 1995;Denoth et al 2002;Cardinale et al 2003;Casula et al 2006). Empirical studies show that increasing diversity of natural enemies can result in a full spectrum of outcomes, including additive, antagonistic, synergistic, or no effects on biological control (Casula et al 2006;Janssen et al 2006Janssen et al , 2007.…”

Intraguild predation involving Harmonia axyridis: a review of current knowledge and future perspectives

“…While 566 the abundance of particular species can be enhanced through biological control, the 567 question of 'how many species are required to achieve the required service in the crop?' 568 continues to be a matter of debate (e.g., Denoth et al 2002;) 569 and must be considered in the context of the arrival of H. axyridis and potential declines in 570 guild diversity. The relationship between predator biodiversity and ecosystem function is 571 poorly understood.…”