Evaluation of Steinernema khuongi and Heterorhabditis downesi as Biological Control Agents Against Four Stored Product Beetle Pests

Storage insects consist a continuous global threat to food safety. In this study, the efficacy of the entomopathogenic nematodes (EPNs) Steinernema khuongi and Heterorhabditis downesi was evaluated against larvae of Tribolium castaneum, Tribolium confusum, Tenebrio molitor, and Trogoderma granarium in wheat and maize at six concentrations and two exposure intervals. Both EPNs exhibited higher virulence when applied in wheat than in maize. Generally, larval mortalities were higher under H. downesi treatments vs. S. khuongi, both in commodities and exposures. Notably, the tested EPNs caused high mortalities to T. granarium larvae (range, 88.9–92.2%) and T. castaneum larvae (range, 81.1–94.4%), respectively, at 10,000 IJs/mL in wheat vs. mortality ranges 72.2–77.8% and 74.4–87.8% in maize, respectively. In contrast, T. confusum larvae were tolerant to both EPNs. Tenebrio molitor larvae were tolerant to S. khuongi (<34.0% mortality) whereas susceptible to H. downesi (>83.3% mortality) at 10,000 IJs/mL in wheat and maize. These findings highlight the potential of S. khuongi and H. downesi as beneficial organisms against several stored-product insect pests.