Fungal parasites of invertebrates: multimodal biocontrol agents?

Introduction Nematophagous and entomopathogenic fungi (NEF) comprise an important group of fungal parasites of invertebrates (FPI). NEF belong to a wide range of fungal taxa, but most of them are anamorphic fungi and facultative parasites. These fungi can infect, kill and digest nematodes and insects, respectively, which we will call their canonical, or normal, hosts. These hosts have barriers to the environment (eggshells and cuticles) that have common structural features. Therefore, the infection cycles share common strategies (e.g. adhesion to the host) or metabolites (e.g. proteases and chitinases for host penetration). Some species (e.g. Lecanicillium lecanii) can even be isolated from both infected nematodes and insects. The NEF may also infect other organisms (other fungi and plants) apart from their canonical hosts in a similar or different mode. We will use the term multimodal to describe the mode of action of these biological activities (Fig. 17.1). However, to date, the main emphasis in research has covered their mode of action on their canonical hosts (e.g. nematodes for nematophagous fungi). Many of these fungi are used for biological control of plant-parasitic organisms. In this review we will describe the NEF and their hosts in general terms (both canonical or non-canonical) at biological, ecological and physiologicalmolecular levels. We will also analyze the reasons for this multitrophic behaviour, trying to use a comparative approach of both types of hosts (canonical and non-canonical) and pathogens (nematophagous and entomopathogenic fungi) under an evolutionary perspective. For recent reviews of the NEF see Charnley (2003); Morton, Hirsh & Kerry (2004); Jansson & Lopez-Llorca (2004).