Prevalence and association of the laboulbenialean fungus Hesperomyces virescens (Laboulbeniales: Laboulbeniaceae) on coccinellid hosts (Coleoptera: Coccinellidae) in Kentucky, USA

James D Harwood,Kevin M Pitz,Roberto Romani,Alex Weir,Carlo Ricci,John J Obrycki

doi:10.14411/eje.2006.109

Abstract

The laboulbenialean fungi occur throughout the world and are closely associated with a range of arthropods, including many coleopteran hosts. Throughout the summer of 2004, coccinellids were collected from a Bluegrass savanna woodland ecosys- tem, dominated by blue ash Fraxinus quadrangulata and Chinkapin Oak Quercus muehlenbergii, and the adults were examined for the presence of Hesperomyces virescens using binocular and scanning electron microscopy. Over 80% of adult Harmonia axyridis, a species previously reported as having a persistent association with the fungus, were infected. No significant differences were observed in incidence on male and female hosts, however, the distribution of fungus differed between sexes. Female H. axyridis had a greater percentage of infection on their elytron compared to other parts of their body whilst male infection was concentrated around their elytra, legs and abdomen. Although infection rates were significantly lower, we report, for the first time, the presence of this fungus on the hosts Cycloneda munda, Brachiacantha quadripunctata and Psyllobora vigintimaculata. This is the first study documenting the incidence of this insect-associated fungus with these native coccinellids of North America. In the samples collected from the Bluegrass savanna, two species (Coleomegilla maculata and Hyperaspis signata) were not infected by this fungus.

Highlights

The association of ectoparasitic laboulbenialean fungi with Coleoptera is widely reported (e.g., Weir, 1993, 1994; Weir & Hammond, 1997; Rossi & Santamaria, 2000; Garcés & Williams, 2004; Riddick & Schaefer, 2005)
Some Coccinellidae are reported as hosts of Laboulbeniales (Weir & Hammond, 1997), relatively few studies document the incidence of their infection on these hosts; for example, they infect Adalia bipunctata (L.) (Weir & Beakes, 1996, Welch et al, 2001), Olla v-nigrum Casey (Weir & Beakes, 1996), and Harmonia axyridis (Pallas) (Garcés & Williams, 2004; Riddick & Schaefer, 2005)
Despite the relatively few reports of insect-host associations between coccinellids and laboulbenialean fungi, the consequence of such interactions, and those with other generalist predators which are known to be important in biological control (Meijer, 1975), could be profound given that some generalist predator communities feed extensively on pest populations in agroecosystems

Summary

Introduction

The association of ectoparasitic laboulbenialean fungi with Coleoptera is widely reported (e.g., Weir, 1993, 1994; Weir & Hammond, 1997; Rossi & Santamaria, 2000; Garcés & Williams, 2004; Riddick & Schaefer, 2005) These obligate, ectoparasitic fungi are estimated to number between 10,000 and 50,000 species worldwide on Coleoptera (Weir & Hammond, 1997), with smaller numbers associated with other host species in the Acari, Blattodea, Dermaptera, Diplopoda, Diptera, Heteroptera, Hymenoptera, Isoptera, Orthoptera and Thysanoptera. Whilst most laboulbenialean fungi have few detrimental effects on their hosts (Whisler, 1968; Weir & Beakes, 1995), some negative fitness consequences from these associations are documented (Bro Larsen, 1952; Strandberg & Tucker, 1974; Gemeno et al, 2004), and have been attributed to causing declines in the summer populations of Chilocorus bipustulatus L. in Israel (Kamburov et al, 1967)

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