Formula optimization of liquid medium for culturing the entomopathogenic nematode Steinernema carpocapsae All (Rhabditida: Steinernematidae).

The successful commercialization of entomopathogenic nematodes (EPNs) as a biopesticide product depends on industrial mass production of viable infective juveniles (IJs) at low cost. This study focused on enhancing the yield of the Steinernema carpocapsae All (Weiser) and reducing its production costs. An optimal basal medium was screened among several basal media, and several optimized components were included in the selected optimal basal medium. The optimal medium formulation was obtained by evaluating the yield, virulence, and survival rates of S. carpocapsae All at different times. The results showed that when isopropylstilbene was added to the basal medium together with insulin, the yield increased from 13.14 × 104 IJs/ml with the basal medium to 19.63 × 104 IJs/ml. At 30 d of low temperature storage, the survival rate increased from 31.42% (basal medium) to 56.83% (optimal medium), demonstrating a prolonged the shelf life. The virulence of S. carpocapsae All was measured before and after 30 d of storage on sponges. The virulence against Tenebrio molitor (Linnaeus) (Coleoptera: Tenebrionidae) and Galleria mellonella (Linnaeus) (Lepidoptera: Pyralidae) was 90 and 86.67% (before) and 93.33 and 94.44% (after), respectively, when insects were treated at 48 h, long-term cryogenic storage has no effect on the virulence. The yield with the individual optimization components added to the optimal basal medium was lower than when the components were combined, indicating that there may be a synergy between the 2 components. The results would provide practical technology for low-cost commercial production of S. carpocapsae All and promote field applications.