Ecological impacts of Heterorhabditis bacteriophora’s inundative treatments

Entomopathogenic nematodes (EPNs) such as Heterorhabditis bacteriophora are biocontrol agents used widely to control insect pests. Inundative treatments with a commercial strain of H. bacteriophora were applied in a Lebanese natural cedar forest attempting to control the principal cedar defoliator, Cephalcia tannourinensis from 2014 till 2016. The aim of this study is to assess the ecological impacts that this application might have on the pedofauna. Three experiments were conducted: the first one measured the persistence of the EPNs following each treatment. The second experiment assessed the interaction that EPNs might have with naturally occurring entomopathogenic fungi, Beauveria bassiana. Baits with the greater wax moth Galleria mellonella were used for these 2 experiments.
Molecular identification was applied on the emerging nematodes to confirm whether they belong to the H. bacteriophora strain or are opportunistic nematodes. Microscopic observation using cadavers with external white sporulation were used to confirm the presence of B. bassiana. The third experiment followed the dynamic of non-targeted insects belonging to the orders of Coleoptera and Hymenoptera (Formicidae family) using wine pitfall traps. Results showed no persistence of EPNs belonging to H. bacteriophora strain. No ecological impacts were detected on neither the presence of B. bassiana nor the non-targeted insects. These results give promising hopes for the use of exotic strains of EPNs in natural forests where urgent treatments are needed for the control of alarming pest outbreaks.