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

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 ·2H2 O 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.

Supplementary information: The online version contains supplementary material available at 10.1007/s10340-021-01349-4.