Restoring Balance: Using Exotic Species to Control Invasive Exotic Species

Invasive species threaten natural habitats worldwide, and active human management is required to prevent invasion, contain spread, or remediate ecosystems following habitat degradation. One powerful technology for invasive species management in sensitive habitats is biological control, the use of carefully selected upper-trophic-level organisms that utilize the exotic pest as a resource, thereby reducing it to less harmful densities. Many in the conservation biology community view this pest-management technology as a high-risk enterprise because of potential collateral damage to nontarget species. The potential benefits arising from successful biological programs are reduced pesticide use, significant pest suppression, and a return to ecological conditions similar to those observed before the arrival of the pest. Biological control as a pest-management strategy has limitations: some pest species may not be suitable targets for biological control because natural enemies may not be sufficiently host-specific and may pose a threat to nontarget organisms. In some instances, substantial effects on nontarget species have occurred because generalist natural enemies established as part of a biological control program heavily utilized other resources in addition to the target pest. To minimize nontarget impacts, regulations governing releases of natural enemies are becoming more stringent, as evidenced in New Zealand and Australia. Voluntary codes of good practice are being advocated by the Food and Agriculture Organization to promote wide adoption of safety measures, which, if followed, should result in the selection of agents with high levels of host and habitat fidelity. Biological control programs in support of conservation have traditionally targeted weed species that threaten natural areas. More recently, exotic arthropod pests that compete with native wildlife or damage native plants have become targets of conservation-oriented biological control programs. Extension of biological control to new targets of conservation importance, such as invasive aquatic invertebrates and pestiferous vertebrates, is warranted. In many instances, once prevention, containment, and eradication options have been exhausted or deemed infeasible, carefully orchestrated biological control programs against appropriately selected targets may be the only feasible way to control invasive species affecting communities under assault from exotic species. Restaurando el Balance: Utilización de Exóticos para Controlar Exóticas Invasoras Resumen: Las especies invasoras amenazan los hábitats naturales en el mundo y se requiere de manejo humano para prevenir la invasión, contener la expansión o remediar ecosistemas después de la degradación de hábitats. El control biológico, el uso de organismos de niveles tróficos superiores cuidadosamente seleccionados que utilizan la especie exótica como recurso reduciéndola a densidades menos dañinas, es una poderosa tecnoloǵıa para el manejo de especies invasoras en hábitats sensibles. Muchos en la comunidad de biólogos de la conservación consideran esta tecnoloǵıa de manejo de plagas como de alto riesgo por el daño colateral potencial a otras especies. Los beneficios potenciales de programas biológicos exitosos son la reducción de usos de pesticidas y un regreso a condiciones ecológicas similares a las observadas antes de la llegada de la plaga. El control biológico como estrategia de manejo de plagas tiene limitaciones; algunas especies de plagas pueden no ser blancos adecuados para el control biológico porque sus enemigos naturales pueden no ser lo suficientemente espećıficos y constituir una amenaza para otras especies. En algunos casos han ocurrido impactos sustanciales porque los enemigos naturales generalistas, utilizados como parte de un programa de control biológico, utilizaron otros recursos intensivamente además de la especie focal. Para minimizar los impactos no deseados, las regulaciones de la liberación de enemigos naturales son cada vez más estrictas Paper submitted June 6, 2002; revised manuscript accepted November 19, 2002.