Attachment of Metarhizium anisopliae to the southern green stink bug Nezara viridula cuticle and fungistatic effect of cuticular lipids and aldehydes.

In this paper we examined the conidial attachment of Metarhizium anisopliae on the southern green stink bug, Nezara viridula, using the exuvia and nymphal stage of the host as a substrate for M. anisopliae conidiospores. Initial studies using fluorescein isothiocyanate (FITC)-labeled conidia examined the differential binding of conidia to various sites on the cuticle. Both the topography and the chemistry of the cuticle affected conidial adhesion. Conidia were trapped in areas containing large numbers of setae (e.g., antennal tips, apical portions of tibia and tarsi). Chemical treatments to remove the cuticle proteins did not affect conidial adhesion, but solvent extraction of cuticular lipids significantly reduced the adhesion of M. anisopliae spores. Germination of M. anisopliae conidia attached to N. viridula cuticle was much less than conidia attached to other insect cuticle substrates. After a 24-hr incubation, only 5-20% of the conidia produced detectable germ tubes. The aldehyde (E)-2-decenal, a primary component of the stink bug scent gland, was detected in cuticle extracts and found to be selectively fungistatic to certain entomopathogenic fungi, including M. anisopliae. The hydrocarbon fraction (nC13 and nC21 to nC31 hydrocarbon series) served as a binding substrate for M. anisopliae, but conidia did not degrade these hydrocarbons and did not use them as a carbon source.