Enteric bacteria of field-collected Colorado potato beetle larvae inhibit growth of the entomopathogens Photorhabdus temperata and Beauveria bassiana

The nematode Heterorhabditis marelatus fails to reproduce in the Colorado potato beetle, Leptinotarsa decemlineata, possibly due to interference from the enteric bacteria of the beetle. Specifically, the enteric bacteria inhibit the growth of Photorhabdus temperata, the enteric symbiont of the nematode, in vitro. However, previous work was based on a laboratory culture of L. decemlineata, and we wished to determine if similar bacteria were present in the field. Therefore, we cultured the enteric bacteria of fourth-instar larvae collected from the field at two locations in Maryland and Virginia. Representatives of the genera Pantoea, Enterobacter, Pseudomonas, Acinetobacter, Serratia, Stenotrophomonas, Curtobacterium, Bacillus, Lactococcus and Enterococcus were identified by sequencing of their 16S rDNA. Isolates belonging to the genera Pantoea, Enterobacter, Pseudomonas, Serratia and Bacillus inhibited the growth of P. temperata. A number of these isolates also inhibited the entomopathogenic fungus Beauveria bassiana in vitro.