Cold tolerance of biological control agents <i>Amblydromalus limonicus</i> and <i>Iphiseius degenerans</i>

Abstract Knowledge about cold tolerance of non‐native biological control agents is critical to avoid permanently establishing them in new temperate areas outside of their native range. The cold tolerance of the predatory mites, Amblydromalus limonicus and Iphiseius degenerans , was investigated in the laboratory to assess their establishment potential in northern Europe, particularly Sweden. The lethal time of I. degenerans (the number of days until 100% mortality was reached) declined steeply from 5°C to 0°C and was almost zero at −5°C. The lethal time of A. limonicus did not differ between 5°C and 0°C, but was reduced at −5°C. For both species, LTime 50 (the number of days until 50% of the mites died) was longer for fed than for unfed mites. The lethal temperature of A. limonicus (the temperature at which 100% mortality was reached) was −17.75°C, whereas most I. degenerans died at −8.5°C. LTemp 50 (the temperature at which 50% of the mites died) was lower for A. limonicus (−9.8°C) than for I. degenerans (−0.1°C). Collectively, these findings suggest that I. degenerans is unlikely to establish in Sweden but that A. limonicus is more cold tolerant. This highlights the risk associated with releasing A. limonicus in Sweden due to concerns about potential establishment.