Reducing phosphine dependence for stored-product pest control with the predatory mite Cheyletus malaccensis in China

The deterioration of grain quality and pests contamination during storage pose significant challenges to global food security. Overreliance on phosphine fumigation has led to widespread resistance in stored-product pests. While the predatory mite Cheyletus malaccensis Oudemans (Acari: Cheyletidae) has shown efficacy in controlling pests in laboratory studies, its operational efficacy within Integrated Pest Management (IPM) for reducing chemical dependency while preserving grain quality lacks systematic evaluation. In this study, a large-scale field validation of the predatory mite Ch. malaccensis as a biological control agent was conducted over a 10-month period. It encompassed 12 grain depots across China's four grain storage ecological zones (IV, V, VI, VII), areas known to be highly susceptible to pest infestations. Under the predator-first IPM protocol, linear mixed-model analysis showed that fumigation frequency and phosphine dosage were significantly lower in warehouses receiving Ch. malaccensis than in conventional fumigation-only warehouses (p = 0.044 and p = 0.023, respectively), while pest densities were maintained below action thresholds. The predator was effective against psocids and certain coleopteran pests such as Cryptolestes ferrugineus , although its efficacy against lepidopteran pests like Sitotroga cerealella was limited. Quality assessment of wheat from one of the depots after 10 months of field storage showed no significant differences in eight key parameters between the test and control warehouses. Overall, a predator-first IPM strategy contributed to reducing fumigant use and showed potential to maintain grain quality in grain storage systems.