Calcium-alginate beads as a formulation for the application of entomopathogenic nematodes to control rootworms

Jinwon Kim,Bruce E Hibbard,Geoffrey Jaffuel,Ted C J Turlings,Ivan Hiltpold,Ilham Sbaiti

doi:10.1007/s10340-021-01349-4

Abstract

Entomopathogenic nematodes (EPN) have great potential as biological control agents against root-feeding insects. They have a rapid and long-lasting mode of action, minimal adverse effects on the environment and can be readily mass-produced. However, they have a relatively short shelf-life and are susceptible to desiccation and UV light. These shortcomings may be overcome by encapsulating EPN in Ca2+-alginate hydrogels, which have been shown to provide a humid and UV protective shelter. Yet, current Ca2+-alginate formulations do not keep EPN vigorous and infectious for a prolonged period of time and do not allow for their controlled release upon application. Here, we introduce solid Ca2+-alginate beads which we supplemented with glycerol to better retain the EPN during storage and to ensure a steady release when applied in soil. Glycerol-induced metabolic arrest in EPN (Heterorhabditis bacteriophora) resulting in quiescence and total retainment of EPN when added to beads made with 0.5% sodium alginate and 2% CaCl2·2H2O solutions. More than 4,000 EPN could be embedded in a single 4–5-mm diameter bead, and quiescence could be broken by adding water, after which the EPN readily emerged from the beads. In a field trial, the EPN beads were as effective in reducing root damage by the western corn rootworm (WCR, Diabrotica virgifera virgifera) as EPN that were applied in water. Although further improvements are desirable, we conclude that Ca2+-alginate beads can provide an effective and practical way to apply EPN for the control of WCR larvae.

Highlights

Entomopathogenic nematodes (EPN) have been shown to be highly effective biological control agents with unique advantages that chemical and other biological pesticides do not have
We developed mass-producible Ca2+-alginate EPN beads that can house and liberate as many as 4,000 EPN per 90-μl bead
EPN incorporated in these beads were stored without refrigeration in a state of glycerol-induced quiescence

Summary

Introduction

Entomopathogenic nematodes (EPN) have been shown to be highly effective biological control agents with unique advantages that chemical and other biological pesticides do not have. The viability and infectivity of IJs decrease over time as energy reserves are depleted This limits the shelf-life of EPN products to maximally a few months even when properly stored (Grewal 2002; Koppenhöfer 2007; Shapiro-Ilan et al 2006). They are highly susceptible to UV radiation, heat and desiccation; many EPN die soon after application due to exposure to air and sunlight, and only a tiny fraction will reach target hosts (Gaugler et al 1997). They are mostly applied in liquid formulations that require proper agitation in storage tanks to prevent the EPN from settling down at the bottom (Shapiro-Ilan et al 2012)

Methods

Results

Conclusion