The thermal biology and thresholds of Phytoseiulus macropilis banks (Acari: Phytoseiidae) and Balaustium hernandezi von Heyden (Acari: Erythraeidae)

Phytoseiulus macropilis Banks (Acari: Phytoseiidae) and Balaustium hernandezi von Heyden (Acari: Erythraeidae) have been identified as candidate augmentative biological control agents for the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). The two-spotted spider mite is a significant pest of many commercial crops, including those grown in glasshouses. This study investigated the potential of both species to survive a typical northern European winter, and risk of establishment. The thermal thresholds of each species were also assessed to determine the efficacy of the predator in a horticultural system. \n \nThrough a combination of laboratory and field trials, P. macropilis was shown to present a low risk of establishment in northern Europe. Survival of winter field exposures was limited to three weeks, and the mite did not demonstrate the ability to enter a diapause state. Similarly, the lower thermal activity thresholds allowed movement of the mite at temperatures where T. urticae became immobile, but were not so low as to pose a threat of dispersal in a northern European winter. The predatory ability of P. macropilis on tomato and French bean leaf surfaces was investigated, and found to be similar to the current leading market predator of T. urticae, Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae). \n \nIn contrast, B. hernandezi demonstrated a high tolerance of northern European winter temperatures, surviving in the field for over four months. Balautium hernandezi was able to move at temperatures where T. urticae became immobile, however, there was some movement at sub-zero temperatures suggesting any escapees from the glasshouse would have the ability to move and survive a typical northern European winter. \n