Interaction between Metarhizium anisopliae CLO 53 and entomopathogenic nematodes for the control of Hoplia philanthus

The interaction between the entomopathogenic fungus Metarhizium anisopliae CLO 53 and the entomopathogenic nematodes Heterorhabditis megidis and Steinernema glaseri against third-instar Hoplia philanthus was studied in a series of laboratory and greenhouse experiments. Insect larvae were exposed to various concentrations of M. anisopliae and nematodes and larval mortality was assessed weekly. Nematodes were added simultaneously or 2, 3, and 4 weeks after application of M. anisopliae. Throughout the experiments, the combined application of M. anisopliae with nematodes increased larval mortality either in an additive or a synergistic way. To achieve stronger synergistic effects, larvae had to be exposed to M. anisopliae for at least 3 or 4 weeks before the addition of nematodes. We observed this interaction between M. anisopliae and both nematode species. The nematode reproduction in insect larvae exposed to the M. anisopliae–H. megidis combination was not significantly higher than in larvae exposed to only H. megidis. The combination of higher concentrations of M. anisopliae with H. megidis resulted in an antagonistic effect on nematode reproduction. In the greenhouse trial, third-instar H. philanthus were placed in 3-L pots with perennial ryegrass (Lolium perenne) treated with M. anisopliae, the nematode H. megidis or S. glaseri, or the combination of fungus and nematode. Combinations of M. anisopliae and nematodes generated a strong synergistic effect only at higher concentrations (2 × 1012 and 2 × 1013 conidia/ha). This effect was observed when M. anisopliae was applied first and followed by the nematodes 4 weeks later. The combined use of M. anisopliae with nematodes may offer an integrated approach to increase the efficacy of entomopathogenic nematodes for H. philanthus control and perhaps other insect pests.