Abstract
The role of predators and parasitoids in the regulation of insect populations is widely reported in the context of both pest and non-pest insects. However, this is not the case for pathogens (entomopathogens). Indeed, most studies on insect life history refer only to predators and parasitoids when considering natural enemy guilds, even though naturally occurring entomopathogens are undoubtedly more diverse and widespread. This is certainly the case with the Coccinellidae; the natural enemies of coccinellids have been the subject of a number of review articles but pathogens receive only brief mention. In this review we attempt to address the balance and consider the interactions of natural populations of Coccinellidae with entomopathogenic fungi. Most research on ento- mopathogens and Coccinellidae focuses on the non-target impact of biorational insecticides against coccinellids and the impact of fungal infections upon aggregations of overwintering coccinellids; with the former overwhelmingly dominating the literature. Given the prominence of coccinellids in classical and conservation biological control, it is surprising that studies have not measured the natural impact of pathogenic fungi upon introduced species or natural populations of Coccinellidae, as has been done with numerous insect pest species. Here we review the literature on the intriguing interactions between coccinellids and fungal pathogens. We examine the literature on direct infection (sub-lethal and lethal) of coccinellids by pathogenic (Beauveria bassiana, Metarhizium ani- sopliae, Paecilomyces fumosoroseus) or parasitic (Hesperomyces virescens). We also consider the role of intra-guild predation (on the aphid-specific fungus Pandora neoaphidis and Beauveria bassiana) and finally indirect interactions such as coccinellids dis- persing P. neoaphidis. We suggest that fungal pathogens are all too often forgotten natural enemies and future research should address the profound absence of knowledge in this field.
Highlights
There have been considerable advances in the field of insect pathology over the last few decades, but the role of pathogens as natural enemies of nonpest insects is seldom considered
Coccinellids are attacked by a suite of natural enemies (Majerus, 1994; Hodek & HonČk, 1996; Roy et al, 2006a, b) including: predators [such as: the predatory bug Deraeocoris ruber L. (Hemiptera: Miridae)], a hymenopteran parasitoid [Dinocampus coccinellae (Schrank) (Hymenoptera: Braconidae)], dipteran parasites [such as Phalacrotophora fasciata Fallén (Diptera: Phoridae)], a mite [Coccipolipus hippodamiae (McDaniel & Morril) (Acari: Podapolipidae)], various male-killing bacteria (Wolbachia, Spiroplasma, Rickettsia) and insect pathogenic fungi [such as Hesperomyces virescens Thaxter (Ascomycota: Laboulbeniales) and Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales)]
Ample research has shown the diversity of natural enemies attacking Coccinellidae, surprisingly little of this information concerns entomopathogenic fungi
Summary
There have been considerable advances in the field of insect pathology over the last few decades, but the role of pathogens (entomopathogens) as natural enemies of nonpest insects is seldom considered. Species in the Entomophthorales do not produce toxins as part of the infection cycle and are obligate pathogens They are characteristically biotrophic and have a narrow host range among foliar arthropods. Similar to the Entomophthorales, the Hypocreales produce resting structures for survival in the absence of new hosts or under adverse environmental conditions Another important group of fungi in relation to coccinellids is the Laboulbeniales (Ascomycota: Laboulbeniaceae). Smaller numbers are thought to be associated with other insect orders (Blattodea, Dermaptera, Diptera, Hemiptera, Hymenoptera, Isoptera, Orthoptera and Thysanoptera) and from noninsect hosts (Acari and Diplopoda) These intriguing fungi are obligate ectoparasites that infect many coccinellids (Thaxter, 1931; Nalepa & Weir, 2007) occurring from the tropics to the sub-Antarctic on both terrestrial and aquatic hosts (Santamaria, 2001; Harwood et al, 2006). It is hypothesised that heavy infections could impede flight, foraging and mating but this requires further investigation
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