Development of the entomopathogenic hyphomycete Lecanicillium muscarium (Hyphomycetes: Moniliales) on various hosts

Hassan Askary,Hamid Yarmand

doi:10.14411/eje.2007.011

Abstract

The present scanning electron microscopy study describes the development of Lecanicillium muscarium, strain DAOM 198499, on the surface of diverse hosts, including Sphaerotheca fuliginea, a fungal host, and Macrosiphum euphorbiae and Aphidius nigripes, insect hosts. The hosts were sprayed with a conidial suspension of L. muscarium (107 conidia/ml). The specimens used in the SEM investigation were collected at particular periods after spraying and prepared for scanning using standard methods. Germination tubes developed twenty-four hours after applying L. muscarium conidia to each host. Hyphae were attached to the host by a thin mucilaginous matrix. Seventy-two hours after spraying, hyphae of S. fuliginea had collapsed and were encircled by the parasite, and primary sporulation of L. muscarium was observed. On the aphid host, colonization started with adherence of the conidia to the host cuticle, followed by conidial germination and growth of mycelium on the surface of the insect's integument. After 48 to 72 h, post colonization, the first sporulation was observed on the cuticle, particularly at articulations. The mode of parasitism of A. nigripes by this fungus was similar to that of the aphid. Development of L. muscarium was observed on both mummified aphids (containing the pupae of parasitoids) and adult parasitoids.

Highlights

For many years considerable attention has been focused on fungi that infect their hosts primarily through their cuticle, because of their potential for reducing populations of sucking insects (Burge, 1988)
Twenty four hours after application of L. muscarium, the antagonist was distinguished from the pathogen by its narrower hyphae (Fig. 1A)
Germ tubes of the parasite excreted a mucilaginous matrix on to the powdery mildew mycelium and conidia (Fig. 1B), and in some cases an appressorial shape was observed at the tip of a germ tube (Fig. 1C, arrow). 48 h after treatment, pathogen damage was more pronounced and mycelial deformation clearly apparent (Fig. 1B, C)

Summary

Introduction

For many years considerable attention has been focused on fungi that infect their hosts primarily through their cuticle, because of their potential for reducing populations of sucking insects (Burge, 1988). The factors determining host specificity and virulence of entomopathogenic fungi are poorly understood and, complementary data characterizing their mode of action is critically required (Clarkson & Charnley, 1996). Infection via the surface of the host is by active penetration and is one of the most important means by which pathogenic fungi infect their hosts. Orientation of germ tubes and attachment to the epicuticle determine the relative virulence of entomopathogenic fungi (St. Leger, 1993; Clarkson & Charnley, 1996). Germinate very quickly and can orientate on the cuticle (Charnley & St. Leger, 1991). Penetration, colonization and sporulation occurs faster in Metarhizium anisopliae (Metsch.) than in B. bassiana, resulting in the earlier death of hosts infected with the former fungus (Moino et al, 2002)

Methods

Results

Conclusion