Grower-Based <em>In Vivo</em> Propagation of Entomopathogenic Nematodes

Entomopathogenic nematodes (EPNs) produced through in vitro or in vivo methods are highly effective biocontrol agents for insect pest management. In vivo mass-propagation systems result in high-quality nematodes but are often more labor-intensive and/or less cost-effective than commercial in vitro methods. Grower-oriented nematode propagation systems described to date are generally unreliable because they rely on external sources (industry or academic laboratories) to calibrate the inoculum. We designed novel grower-based systems where farmers can continuously produce their own nematodes after acquiring inoculum from established EPN production laboratories/companies. Here, we present two methods for farmers to mass-propagate EPNs as bio-insecticides. In the first method, we compared in vivo nematode production using the standard White trap method to a grower-oriented approach involving polyacrylamide gel as the nematode substrate. The grower-oriented method produced more nematodes than the standard method when culturing two commonly available EPN species (Steinernema carpocapsae and Heterorhabditis bacteriophora). In the second method, two native nematode species (Oscheius onirici and Heterorhabditis georgiana) were mass-propagated within live beetle larvae (Tenebrio molitor) that were embedded between two layers of a polymer-coated cotton wool. Harvesting the emerged nematodes from the wool bilayer employed systematic irrigation of a tray, creating a nematode slurry ready for field applications. These grower-oriented systems hold promise for wide adoption by agricultural stakeholders because the approaches are technically simple and scalable for those who seek accessible, reliable methods to produce nematodes. By providing growers a means to create their own pest management tools, these methods should facilitate greater independence and profitability on US farms.