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Abstract

ABSTRACT:The mode of infection of Nomuraea rileyi in Spodoptera litura larvae was examined using local strains isolated from infected larvae of S. litura collected from the field in Mae Chaem district, Chiang Mai province, Thailand. Spore suspensions were topically applied to larvae followed by examination using standard histological techniques. Germ tubes penetrated through the cuticle surface within 48 hr after inoculation and then along the cuticle. Lysis of the endocuticle was found before hyphae penetrated and invaded the epidermis ca. 2.5 days after inoculation. The invasive hyphal stage then transformed into hyphal bodies that replicated within the hemocoel. These non-invasive hyphal bodies filled the hemocoel and then converted to invasive mycelia ca. 5-6 days after inoculation. At the end of the infection cycle, mycelium emerged from the cuticle and produced condiophores ca. 7 days after inoculation. The larvae became completely covered by white mycelium before turning green 1-2 days later as a result of spore production. The complete developmental cycle of N. rileyi in S. litura lasted approximately 8 to 9 days. List of abbreviations: List of abbreviations: List of abbreviations: List of abbreviations:List of abbreviations: bc, blood cell; Cu, cuticle; D, dermal cell; ed, endocuticle; ep, epicuticle; epd, epidermis cell; ex, exocuticle; FMAY, fish-soluble medium supplement with 1% maltose, 1% yeast extract and 1.5% agar; hb, hyphal body; hp, hyphae; m, muscle; µm, micron; nu, nucleus.

Isolation of ergosterol peroxide from Nomuraea rileyi infected larvae of tobacco cutworm

“…We found that extracts of diseased larvae at 2 and 5 days post infection had little if any activity whereas extracts of mycosed larvae (7, 8 days post infection) produced significant cell death of the assayed Sf9 cells. In terms of fungal development, the 2 and 5 day extractions represent extracts of infected insects harboring penetrant germ tubes and hemocoelic hyphal bodies, respectively (Boucias and Pendland 1982;Srisukchayakul et al 2005). The 7 and 8 day extracts contain metabolites produced by the tissue invasive and conidiophore-producing mycelial phenotypes.…”

A life-and-death struggle: interaction of insects with entomopathogenic fungi across various infection stages

“…Following the attachment of EPF conidia to the host cuticle, appressoria may form at the tips of fungal germ tubes, displaying apical swelling structures adhering to the host cuticle with diverse morphologies (e.g., clavate, spherical, or cup-shaped structures) ( 53 – 55 ) ( Figure 1A ). However, certain EPF species, like Metarhizium rileyi , do not undergo appressorium formation, in which the germ tubes grow along the endocuticle and produce lateral branches ( 56 ). M. anisopliae can occasionally penetrate the cuticle directly without appressoria formation ( 57 ).…”

Multifunctional regulation of NADPH oxidase in growth, microsclerotia formation and virulence in Metarhizium rileyi

“…Conidia are the main virulent determinants of fungal pathogenicity; once attaching to cuticle, conidia will germinate rapidly to produce appressoria, convert to penetration pegs to penetrate and enter into insects, then intrusive hyphal body began to proliferate sharply, compete and consume host nutrients, secrete toxins into insect hemocoel, and result in the death of insect eventually. Later, hyphostroma inside insect will transform into mycelium to destroy insect body wall and produce conidia to enter the next infection cycle (Srisukchayakul, 2005). All these unique infection mechanism suggest that fungal biological pesticide will be an extensive perspective of agricultural application.…”

“…After occupying the haemolymph, hyphal body then transformed into slender invasive mycelium, penetrating the insect body wall, and eventually kills host insects. Due to the lack of receptors recognized by the host immune system on cell surface, yeast like hyphal body can escape from the host immune defense and proliferate rapidly in the blood cavity, but there is no infection ability of hyphal body and prolonging of the yeast phase would be not conducive to the pathogenicity of entomogenous fungi(Srisukchayakul et al, 2005;Egan et al, 2007;Ryder et al, 2013). Virulence test…”