Mite incidence in Egyptian storage facilities and acaricidal activity of selected monoterpenes, phenylpropenes, and sesquiterpenes against Suidasia medanensis Oudemans (Astigmata: Suidasiidae), a formidable storage mite pest

Mite pests cause significant postharvest losses to the world's food supply, where substandard storage conditions and lack of effective control enable mites to replicate. Therefore, the aim of this study was to assess mite infestation risk and determine the acaricidal efficacy of some monoterpenes, phenylpropenes, and sesquiterpenes against one of the most prevailing mite pests found in Egyptian storage facilities. A screening mite survey was conducted on bran and flour samples obtained from commercial stores and flour mills in Alexandria, Egypt between June and December 2019. Eight mite taxa belonging to five families were identified. Tyrophagus putrescentiae (Schrank) (Acaridae) and Suidasia medanensis Oudemans (Suidassidae) were the most dominant species, each representing ≃ 40% of the total mite count (142,988 individuals). Cheyletus malaccensis Oudemans (Cheyletidae) was the most abundant predatory mite recorded in both storage sites. The contact toxicity of eight compounds belonging to monoterpenes, phenylpropenes, and sesquiterpenes was evaluated against the adults of S. medanensis. trans-Cinnamaldehyde showed the highest acaricidal activity, followed by eugenol, cuminaldehyde, (Z,E)-nerolidol and farnesol with LC50 values of 0.007, 0.028, 0.036, 0.042 and 0.048 mg/cm2, respectively, after 24 h of treatment. The toxicity of all compounds against the adults increased after 48 h, indicating that the effectiveness of compounds improved with increase of exposure time. On the other hand, the tested compounds showed different levels of repellent activity against S. medanensis adults after 1 and 6 h of treatment. The highest repellent effects were observed in the case of (Z,E)-nerolidol and farnesol displaying repellency of 92.0–96.3 and 81.4–92.1%, respectively, after 1 h of treatment. In contrary, (-)-citronellal and cuminaldehyde showed the lowest repellent effect. These results indicate that the tested compounds, particularly phenylpropenes and sesquiterpenes, could be effective candidates for the management of S. medanensis in storage products.