Wireworms, the polyphagous larvae of click beetles belonging to the genus Agriotes (Coleoptera: Elateridae), are severe and widespread agricultural pests affecting numerous crops. A previously unknown intracellular bacterium has been identified in a diseased Agriotes larva. Microscopic studies revealed the subcellular structures characteristic of Rickettsiella infections. Molecular phylogenetic analysis based on 16S ribosomal RNA and signal recognition particle receptor (FtsY) encoding sequences demonstrates that the wireworm pathogen belongs to the taxonomic genus Rickettsiella. Therefore, the new pathotype designation 'R. agriotidis' is proposed to refer to this organism. Moreover, genetic analysis makes it likely that--on the basis of the currently accepted organization of the genus Rickettsiella--this new pathotype should be considered a synonym of the nomenclatural type species, Rickettsiella popilliae.