Dispersal ability of the predatory mites Blattisocius tarsalis and Cheyletus malaccensis in grain piles and storage facilities

Abstract

Predatory mites can be released into storage facilities to control various stored product pests. However, their ability to disperse within grain piles and structures (warehouses and processing facilities) has not been well assessed. This study aimed to evaluate two predatory mites, Blattisocius tarsalis and Cheyletus malaccensis, as biological control agents by examining their dispersal abilities in piles of rice grains and storage facilities. The mites were evaluated for their capacity to navigate vertically through polyvinyl chloride (PVC) tubes filled with paddy rice at depths of 40 and 100 cm to determine if they could reach the eggs of various lepidopteran pests at the bottom. Additionally, their dispersal ability over varying time intervals and their preferences concerning light intensity were assessed in 2-metre-long channels coated with rice flour residues. An integrated assessment of their vertical and horizontal dispersal capacities, along with the influence of light, was conducted in a controlled pilot storage room (4 × 3 × 3 m). Blattisocius tarsalis demonstrated impressive dispersal capabilities, reaching pest eggs at vertical depths of 40 and 100 cm through rice and dispersing 2 m horizontally in just 4 h. This proficiency extended to pilot storage room conditions, where it successfully navigated all distances, both horizontally and vertically, showing a preference for navigating away from the light. Cheyletus malaccensis proved to be an effective predator at close range to pest eggs but demonstrated limited dispersal capabilities in complex setups. This study underlines the suitability of B. tarsalis as a biological control agent capable of dispersing in various environments. Conversely, the utility of C. malaccensis may be more specialised and effective within a narrow movement range. These findings highlight the importance of understanding mite dispersal behaviours for optimising pest management strategies and contributing to the more sustainable and effective storage of rice grains.