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Adult mites Balaustium murorum collected from a wild population died in laboratory storage containers and became mouldy. The fungus was identified as Purpureocillium lilacinum (predominate isolate) by 98% internal transcribed spacer (ITS) and beta-tubulin (Bt2a/Bt2b) BLAST match to authentic strains from soil. Larvae, deutonymphs, and adults could be artificially infected by topical application with a 107/ml spore inoculum, resulting in rapid dehydration and an increased mortality. This strain of P. lilacinum was more virulent to larvae than post-larval stages. Post-treatment, P. lilacinum was re-isolated internally with high frequency from cadavers. This P. lilacinum has a 25°C optimal growth temperature, 20-35°C thermal growth range, 0.997 aw optimal water activity (aw), and a minimum 0.96 aw to produce spores. Results indicate that infection with P. lilacinum can occur for population control, most likely during periods of moderate temperature and frequent rainfall. Because P. lilacinum is commercially available as a nematocide, application of P. lilacinum may reduce the effectiveness of Balaustium for plant pest control. This strain P. lilacinum UAMH 11932 is pathogenic to B. murorum and it has been deposited at the University of Alberta Microfungus Collection and Herbarium, Toronto, CAN. [ABSTRACT FROM AUTHOR]