Thermal biology of the spider mite predator Phytoseiulus macropilis

Phytoseiulus macropilis Banks (Acari: Phytoseiidae) is a specialist predator of the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae), and has been used to control the pest in its native range: Mediterranean regions, the tropics and Florida, USA. This study investigates the thermal biology as a proxy for establishment potential of glasshouse escapees in cooler northern European climates, using a combination of laboratory and field trials. High mortality rates at 10 °C indicated limited acclimation ability. Mites displayed continuous oviposition in conditions that have previously been shown to induce a hiatus in other phytoseiid species, supporting previous findings that Phytoseiulus is a genus with no diapause state. Adult P. macropilis supercooled to between −17.2 and −24.0 °C, but the lower lethal temperature₅₀ was −5.7 °C, resulting in a high level of pre-freeze mortality. The lethal time₅₀ at 5 °C was 2.6 days, and maximum survival in winter field trials across 2010 and 2011 was 21 days. The thermal biology data indicate that P. macropilis is unlikely to establish in northern Europe, and will therefore make a suitable glasshouse biological control agent in temperate climates.