Optimizing Cheyletus malaccensis releases for the biocontrol of Liposcelis bostrychophila: Density-dependent efficacy in stored grains.

Cheyletus malaccensis (Oudemans), a generalist predatory mite, is a highly promising biocontrol agent applied for stored products pests management in grain storage systems. To optimize its field deployment, this study evaluated the population dynamics of C. malaccensis and Liposcelis bostrychophila (Badonnel) under varying predator-prey ratios (PPRs: 1:9, 1:5, 1:3, 1:1, 3:1) at 26.0 ± 0.1 °C and 75.0 ± 0.5% relative humidity in simulated grain storage environments. During the 49-day post-release period, the peak population reduction rates of L. bostrychophila at four PPRs (1:5, 1:3, 1:1, 3:1) reached 74.87%, 76.61%, 87.10%, and 95.90% respectively, whereas the 1:9 PPR treatment resulted in progressive pest population growth. Conversely, C. malaccensis population establishment rates increased exponentially with decreasing PPRs, peaking at 1,161.11% (1:9 PPR). These findings demonstrate a density-dependent trade-off: higher PPRs maximize short-term pest suppression, while lower ratios enhance long-term predator persistence. Therefore, we propose a two-phase deployment strategy: (i) preventive low-density releases (PPR < 1:5) prior to pest outbreaks to establish mite populations, and (ii) threshold-triggered supplementary releases based on real-time pest monitoring to achieve economical and long-term control of stored grain pests.