Optimal Timing, Temperature, and Duration for Locusta migratoria Egg Mass Storage

Locusta migratoria eggs use diapause and cold tolerance mechanisms, supporting potential for mass rearing. Long-term cold storage conditions for maintaining egg hatching rates remain understudied. This study aimed to determine optimal cold storage conditions for long-term preservation of L. migratoria egg masses. Eggs were stored at 7.5°C for 1 month starting on Days 1, 3, 6, and 9 after oviposition. The highest hatching rate (96.3%) was observed when storage began on Day 6 after oviposition, and no hatching occurred when initiated on Day 1. Among the temperatures tested (5°C, 7.5°C, 10°C, 12.5°C, and 15°C), 10°C yielded the highest hatching rate at 1 month (74.3%), followed by 7.5°C (69.3%). The lowest hatching rate (26.4%) was recorded at 5°C. Egg masses stored at 7.5°C and 10°C maintained high hatching rates (81.1%–86.9%) over a 10-day observation period, even after 5 months of storage. Regression analysis estimated maximum storage durations for maintaining hatching rates ≥ 90% as 2.8–3.9 months at 7.5°C, 2.3–3.8 months at 10°C, and only 0.6 months at 5°C. Notably, eggs stored at 7.5°C for 4 months beginning on Day 6 after oviposition exhibited a hatching rate > 90%, confirming the condition's suitability for extended preservation. Moreover, prolonged storage was associated with shorter hatching durations, suggesting continued embryonic development during cold storage. Thus, initiating cold storage at 7.5°C–10°C 6-day postoviposition allows effective long-term preservation of L. migratoria egg masses, contributing to the establishment of stable, year-round rearing systems.