Conidia of the insect pathogenic fungus, Metarhizium anisopliae , fail to adhere to mosquito larval cuticle

Abstract

Adhesion of conidia of the insect pathogenic fungus, Metarhizium anisopliae, to the arthropod host cuticle initially involves hydrophobic forces followed by consolidation facilitated by the action of extracellular enzymes and secretion of mucilage. Gene expression analysis and atomic force microscopy were used to directly quantify recognition and adhesion between single conidia of M. anisopliae and the cuticle of the aquatic larval stage of Aedes aegypti and a representative terrestrial host, Tenebrio molitor. Gene expression data indicated recognition by the pathogen of both hosts; however, the forces for adhesion to the mosquito were approximately five times lower than those observed for Tenebrio. Although weak forces were recorded in response to Aedes, Metarhizium was unable to consolidate firm attachment. An analysis of the cuticular composition revealed an absence of long-chain hydrocarbons in Aedes larvae which are thought to be required for fungal development on host cuticle. This study provides, to our knowledge, the first evidence that Metarhizium does not form firm attachment to Ae. aegypti larvae in situ, therefore preventing the normal route of invasion and pathogenesis from occuring.

Highly specific host-pathogen interactions influence Metarhizium brunneum blastospore virulence against Culex quinquefasciatus larvae

“…In this study, Culex larvae infected with blastospores produced higher levels of phenoloxidase than that observed during infection with conidia and PO was detected one hour earlier in larvae infected with blastospores when compared to larvae infected with conidia and much earlier than that reported for Ae. aegypti larvae [14]. These observations show that not only is the Culex immune response different from that of Aedes but PO plays a more important role in the former, which is supported by the fact that melanisation at infection sites and of circulating blastospores was only observed in Culex larvae.…”

“…aegypti larvae through multiple penetration sites with blastospores readily adhering and penetrating the insect cuticle as well as penetrating the gut epithelium following ingestion by the larvae [12]. In contrast, conidia of the same fungus fail to adhere to the larval cuticle but cause death through protease-induced stress following ingestion [13,14]. There were, however, clear differences in the susceptibility of Cx.…”

“…Interestingly, conidia of the same fungus kill Aedes larvae using a different process. Conidia do not adhere to the larval cuticle but kill the larvae by protease-induced stress following ingestion of large numbers of these propagules [13,14]. However, the virulence pattern of the two fungal spore forms when tested against Culex quinquefasciatus larvae was different to that seen against Aedes larvae.…”

Entomopathogenic fungi: unconventional applications

“…The first stage of the fungal infection process is spore adhesion to the surface of the arthropod's body. In this stage, two types of proteins are produced: hydrophobins (whose layers disintegrate during the sporulation of spores) and adhesins (MAD1 and MAD2), which enable both close adhesion to the insect's cuticle and recognition of the host by the fungal pathogen (Wang and Leger 2007;Greenfield et al 2014).…”

Effects of Entomopathogenic fungi and Bacillus thuringiensis‐based biopesticides on Spoladea recurvalis (Lepidoptera: Crambidae)

“…The mode of action of EPF involves conidial attachment to the host surface followed by germination and penetration of the host cuticle through a combination of enzymatic activity and mechanical force (Arruda, Lübeck, Schrank, & Vainstein, 2005;Inglis et al, 2012;Quintela & McCoy, 1998). However, some insects have evolved a number of mechanisms to keep pathogens at bay that include (a) production of cuticular antimicrobial lipids, proteins and metabolites (Greenfield, Lord, Dudley, & Butt, 2014;Pedrini et al, 2015); (b) shedding of the cuticle during development; (c) behavioural-environmental adaptations such as induced fever, burrowing and grooming (Oi & Pereira, 1993;Siebeneicher, Bradleigh, & Kenerley, 1992).The low pathogenicity of the selected EPF isolates to S. recurvalis larvae could be due to cuticular or behavioural environmental adaptations that warrant further research to elucidate the exact reasons for this low pathogenicity reported in the present study.…”