Properties of Enhanced Calcium-alginate Beads as a Formulation for Disseminating the Entomopathogenic Nematodes Heterorhabditis bacteriophora, Steinernema carpocapase, and Steinernema feltiae

Calcium alginate beads are one of the substrates used to formulate and store the infective juveniles (IJs) of entomopathogenic nematodes (EPNs). Due to the sensitivity of EPNs to heat, cooling devices are needed to transfer them from the production site to the field or greenhouse. Therefore, it is important to develop a formulation that can be stored at room temperature. The hypothesis of this study was that nematodes formulated in alginate beads would be more stable at room temperature than in sterile water. To compare and select the optimal conditions, formulations were tested at two temperatures: 25 and 8 Celsius (ºC). The formulation included sodium alginate (1.5–1.75%), glycerin, nematode suspension in distilled water (~15,000 IJs), food coloring, and two proprietary water-absorbent compounds. The suspension was added to CaCl₂ (8:2 CaCl₂: glycerin) to create calcium alginate beads. The beads were stored at 8 ºC and 25ºC with a control treatment consisted of sterile water. The study measured survival, reproduction rate, and infectivity of Heterorhabditis bacteriophora, Steinernema carpocapsae, and S. feltiae IJs in calcium alginate beads over time (1–180 days post-formulation). The survival rate of IJs in bead formulations was significantly higher than in the water control treatment. H. bacteriophora experienced higher survival at 25ºC, while S. carpocapsae experienced higher survival at 8ºC. S. feltiae’s survival was not affected by temperature. The pathogenicity of EPNs did not decrease over time. Calcium alginate effectively encapsulated living IJs of various EPN species, keeping them alive for up to three months at room temperature. These results suggest that alginate beads are a suitable material for EPNs formulation. Further research is needed to enhance the efficacy and economic viability of these formulations.