Inhibition of the entomopathogenic fungus Metarhizium anisopliae sensu lato in vitro by the bed bug defensive secretions (E)-2-hexenal and (E)-2-octenal

Abstract

The two major aldehydes (E)-2-hexenal and (E)-2-octenal emitted as defensive secretions by bed bugs Cimex lectularius L. (Hemiptera: Cimicidae), inhibit the in vitro growth of an isolate of Metarhizium anisopliae sensu lato (s.l.) (Metsch.) Sokorin (Hypocreales: Clavicipitaceae) (ARSEF 1548). These chemicals inhibit fungal growth by direct contact and via indirect exposure (“fumigation”). Fumigation with (E)-2-octenal for as little as 0.5 h was sufficient to inhibit all fungal growth. Bed bugs placed on filter paper treated with an isolate of M. anisopliae s.l. conidia in the absence of (E)-2-octenal exhibited 99 % mortality after one week. However, bed bugs placed on fungal-treated filter paper and exposed to (E)-2-octenal at 1 h experienced 10 % mortality. The inhibition of fungal growth by bed bug aldehydes is discussed in the context of other biotic and abiotic barriers to infection.