Bacteria from the Midgut of Common Cockchafer ( L.) Larvae Exhibiting Antagonistic Activity Against Bacterial Symbionts of Entomopathogenic Nematodes: Isolation and Molecular Identification.

The mechanisms of action of the complex including entomopathogenic nematodes of the genera and and their mutualistic partners, i.e., bacteria and , have been well explained, and the nematodes have been commercialized as biological control agents against many soil insect pests. However, little is known regarding the nature of the relationships between these bacteria and the gut microbiota of infected insects. In the present study, 900 bacterial isolates that were obtained from the midgut samples of larvae were screened for their antagonistic activity against the selected species of the genera and . Twelve strains exhibited significant antibacterial activity in the applied tests. They were identified based on 16S rRNA and , , or gene sequences as , , , , sp., , and sp. The culture filtrate of the isolate MMC3 L3 04 exerted the strongest inhibitory effect on the tested bacteria. The results of the preliminary study that are presented here, which focused on interactions between the insect gut microbiota and mutualistic bacteria of entomopathogenic nematodes, show that bacteria inhabiting the gut of insects might play a key role in insect resistance to entomopathogenic nematode pressure.