Enhancing heat tolerance and delivery efficiency of entomopathogenic nematodes with glycerol-calcium alginate gel beads

Entomopathogenic nematodes (EPNs) are promising agents for the biological control of white grubs due to their rapid action, environmental compatibility, and high target specificity, particularly given their shared ecological niche with white grubs.However, their large-scale application is constrained by poor heat tolerance, transportation challenges, and the need for repeated applications.In this study, 15% glycerol was identified as an effective protectant for Heterorhabditis bacteriophora HL6 dormant nematodes during encapsulation.Further optimization revealed that 0.7% sodium alginate, crosslinked with calcium ions, was optimal for preparing calcium alginate gel (EPN@CAG) beads capable of sustained release of EPNs.Increasing the EPN loading density to 400 infective juveniles per bead enabled controlled release over a period of 10 days.Scanning electron microscopy confirmed that EPNs were effectively encapsulated within the beads and released through surface pores.Mechanical and thermal evaluations demonstrated that the beads could withstand up to 45 N of pressure and improved the survival rate of EPNs at 30 C, 35 C, and 40 C.Insecticidal assessments using Holotrichia parallela larvae confirmed their sustained pest control performance.These findings offer a viable solution for deploying microbial biocontrol agents in challenging environmental conditions.