Entomopathogenic nematodes and their symbiotic bacteria for the biological control of Hoplia philanthus (Coleoptera: Scarabaeidae)

Larvae of scarabaeid beetle Hoplia philanthus cause severe problems on sports turf, lawns, and pastures. The efficacy of three species of entomopathogenic nematodes, Heterorhabditis megidis, Steinernema feltiae, and Steinernema glaseri was tested against third instar of H. philanthus. In a dose response experiment, 0, 1, 10, 100, 1000, and 10,000 infective juveniles (IJs) were inoculated in wells of 24-well plates containing sand and a single H. philanthus larva. S. glaseri was most effective (LC50=4.6 and LC90=79.3 after 7 days exposure of IJs/larva) compared to H. megidis (LC50=9.7 and LC 90 =511.8 IJs / larva ). The lethal concentration of S. feltiae could not be determined because of the strain’s low virulence against third instar H. philanthus. In a second experiment, the pathogenicity of the symbiotic bacteria Photorhabdus luminescens, Xenorhabdus bovienii, and Xenorhabdus poinarii was studied. Three microliters of a bacterial suspension (containing 0, 25, 250, 2500, or 25,000 cells) were injected into the hemocoel of third instar of H. philanthus and last instar Galleria mellonella. P. luminescens and X. bovienii killed 100% of the larvae of both species after 72 h; X. poinarii caused lowest mortality for both insect species. In a third experiment, 3 μl of a cell-free filtrate of P. luminescens, X. bovienii, and X. poinarii were injected into the hemocoel of third instar of H. philanthus and last instar G. mellonella. The filtrates of P. luminescens and X. bovienii caused 100% mortality after 24 h to H. philanthus and G. mellonella. The X. poinarii filtrate was least toxic to both insect species. In pot trials, H. megidis and S. glaseri caused more than 80% mortality of H. philanthus larvae infesting potted perennial ryegrass 42 days after application of 2.5–7.5 billion nematodes/ha. The mortality was greater than the grub mortality caused by either S. feltiae (16%) or the control (10%).