Enhancing the shelf life of entomopathogenic nematodes formulation: The impact of super absorbent polymer and infective juveniles concentration

Abstract

Entomopathogenic nematodes (EPNs) from the families Heterorhabditidae and Steinernematidae are promising biological control agents against various insect pests. However, one major limitation to their commercial use is their limited shelf life during storage. This study aimed to evaluate the impact of incorporating a super absorbent polymer (A200) into carboxymethyl cellulose (CMC) formulations of infective juveniles (IJs) of Steinernema carpocapsae on its shelf life over a six-month period at two-month intervals. The experiment was designed as a factorial design, examining the combined effects of varying concentrations of super-absorbent polymer (2% and 4% v/v), EPN concentration (4 × 104 and 8 × 104/mL), and type of antimicrobial agent (formaldehyde 0.2% or sorbic acid 0.25%) on the shelf life of the CMC-based formulation. Our findings indicate that the type of antimicrobial agent significantly affects EPN survival rates during storage. By the end of the second month, the survival rate of non-antimicrobial treated samples had decreased sharply (≤0.2%). Notably, the highest survival rate (91.50%) was observed in the CMC formulation containing 4 × 10³ IJ/mL of nematodes loaded with 2% super-absorbent polymer and treated with formaldehyde. Moreover, our data suggest that the CMC-based formulation containing 4 × 104 IJ/mL of IJs, 4% super-absorbent polymer, and sorbic acid as an antimicrobial agent exhibits superior shelf life for extended storage periods at room temperature. Additionally, we found no significant decrease in EPN virulence towards fourth instar larvae of Anagasta kuehniella after six months of storage. Overall, this study underscores the intricate interplay between formulated IJs concentration and abiotic factors, such as super absorbent concentration and antimicrobial agents, in influencing the stability of EPN formulations. It offers valuable insights for developing more effective and longer-lasting EPN-based products.