The effects of isothiocyanates on the growth of the entomopathogenic fungus <e1>Metarhizium anisopliae</e1> and its infection of the mustard beetle

<e1>Metarhizium anisopliae</e1> has potential as a biological control agent. Included among its hosts are certain insect pests of brassica crops. <e1>Brassica</e1> species produce isothiocyanates, some of which are known to be fungitoxic. In our study, isothiocyanates inhibited both germination and subsequent growth by <e1>M. anisopliae in vitro</e1> and its ability to infect insects. Conidia were more sensitive than the mycelium to these compounds, the most fungistatic of which were phenylethyl-, 2-chlorophenyl- and allyl-isothiocyanates. Appressorium production <e1>in vitro</e1> was suppressed by all isothiocyanates except allyl- and propyl-isothiocyanates, which appeared to stimulate appressorium formation. Phenylethyl- and 3-butenyl isothiocyanates, which are present in several of the plant hosts of <e1>Phaedon cochleariae</e1>, reduced the pathogenicity of <e1>M. anisopliae</e1> when inoculated insects were exposed to their vapours. These findings have implications for the efficacy of biocontrol of brassica pests by this fungus.