Selective breeding of entomopathogenic nematodes for enhanced attraction to a root signal did not reduce their establishment or persistence after field release

We recently showed that the efficacy of an entomopathogenic nematode (EPN) as a biological control agent against a root pest could be enhanced through artificial selection. The EPN Heterorhabditis bacteriophora was selected for higher responsiveness towards (E)-beta-caryophyllene (E beta C), a sesquiterpene that is emitted by maize roots in response to feeding damage by the western corn rootworm (WCR). E beta C is normally only weakly attractive to H. bacteriophora, which is one of the most infectious nematodes against WCR. By selecting H. bacteriophora to move more readily along a E beta C gradient we obtained a strain that was almost twice more efficient in controlling WCR population in fields planted with an E beta C-producing maize variety. However, artificial selection for one trait may come at a cost for other important traits such as infectiousness, establishment and/or persistence in the field. Indeed, infectiousness was slightly but significantly reduced in the selected strain. Yet, this apparent cost was largely compensated for by the higher responsiveness to the root signal. Here we show that the selection process had no negative effect on establishment and persistence of field-released EPN. This knowledge, combined with the previously reported results, attest to the feasibility of manipulating key traits to improve the efficacy of beneficial organisms.