Abstract
Parasites can reduce host body condition, impair reproduction, and cause mortality. However, parasites are a major source of biodiversity, are a fundamental component of a healthy ecosystem, and could be the group most affected by the modern-day biodiversity crisis. Parasite control may cause immunological naivety, unbalance parasite-mediated apparent competition between hosts, and destabilize the host–parasite arms race. Here, we rank parasite control strategies according to their potential impact on ecosystems. We argue that, as the threat that a parasite poses to host survival increases, the need for parasite control increases, and, therefore, control measures that have a greater impact on ecosystems can be justified. However, because host-specific parasites may be more endangered than their hosts, there is often the need for active parasite conservation strategies such as establishing parasite refugia. Although the principles proposed here are predominantly intuitive, there are numerous examples in which they have not been applied.