Alcaligenes sp., Bacillus cereus var. mycoides, Bacillus circulans, Bacillus sp., Escherichia intermedia, Enterobacter aerogenes, Flavobacterium sp., Streptomyces sp., and 2 unidentified gram-negative rods were isolated from the digestive tracts of 24 field-collected larvae of Prionus laticollis kept in the laboratory for 1 week or more. B. cereus var. mycoides, E. aerogenes, E. intermedia, and the unidentified rods were isolated from each larva examined within 24 hr of collection. Other types of micro-organisms were not isolated on the culture media used. Attempts to culture anaerobic bacteria from 12 larvae gave no results. B. cereus var. mycoides and a species of Cephalosporium were isolated from dead pupae and Paecilomyces (= Isaria) farinosa was found on dead last stage larvae (prepupae).