Host and Penetration Site Location by Entomopathogenic Nematodes against Japanese Beetle Larvae

Entomopathogenic nematodes are soil-inhabiting parasites of insects. Behavioral responses to host and host environmental cues are critical steps in the infection process for some nematode species, such asSteinernema glaseriandHeterorhabditis bacteriophora,of finding, recognizing, and penetrating insects. We investigated the impact of host and host environmental cues on the infectivity of these two nematodes by testing their response to whole and wounded grass roots and gut fluid and hemolymph ofPopillia japanicalarvae. We also compared the influence of root presence on infectivity. Infective juveniles of both nematode species migrated to whole and wounded grass roots, suggesting that these nematodes may use cues from grass roots and root wounds for host habitat finding. Root presence enhanced the infectivity ofS. glaseri,presumably because feeding larvae ingest more nematodes than nonfeeding ones. However, the infectivity ofH. bacteriophorawas not enhanced by grub feeding. This may due to the weak gut penetration ability of this species. We conclude that the two species respond similarly to host and host environmental cues but achieve infection differently via penetration:S. glaseripossesses superior gut penetration ability, whereas intersegmental areas such as leg and maxilla joints serve as cuticle penetration sites forH. bacteriophora.