Thermal thresholds of the predatory mite Balaustium hernandezi.

ABSTRACT

The lower and upper thermal activity thresholds of adult and larval Balaustium hernandezi von Heyden (Acari Erythraeidae) are compared with those of its prey Tetranychus urticae Koch (Acari Tetranychidae). Adult female B. hernandezi retain ambulatory function (CTmin) and movement of appendages (chill coma) at significantly lower temperatures (5.9 and -2.1 °C, respectively) than those of larval B. hernandezi (8.1 and -1.7 °C) and T. urticae (10.6 and 10.3 °C). There is no significant difference between the temperature at which adult and larval B. hernandezi and T. urticae cease walking as the temperature is raised (CTmax) (46.7, 46.3 and 47.3 °C, respectively). However, both life stages of B. hernandezi cease movement (heat coma) below the upper locomotory limits of T. urticae (46.8, 46.7 and 48.7 °C, respectively). Adult B. hernandezi have significantly faster walking speeds than larvae and T. urticae across a range of temperatures. The lower thermal activity threshold data indicate that B. hernandezi would make an effective biological control agent in temperate climates; however, the extent of the low temperature tolerances of the species suggests the potential to establish in a northern European climate.