Effects of acclimation and diapause on the thermal tolerance of the two-spotted spider mite Tetranychus urticae

Abstract

The two-spotted spider mite, Tetranychus urticae, is a worldwide pest species that overwinters as diapausing females. Cold hardening is presumed to start during diapause development to ensure the successful overwintering of this species. To address this hypothesis, we compared cold tolerance between non-diapausing and diapausing females. We measured supercooling point (SCP) and survival to acute cold stress by exposing the mites at a range of sub-zero temperatures (from −4 to −28°C for 2h). The mean SCPs of non-diapausing and diapausing females were −19.6±0.5 and −24.7±0.3°C respectively, and freezing killed the mites. Diapausing females were significantly more cold tolerant than non-diapausing ones, with LT50 of −19.7 and −13.3°C, respectively. Further, we also examined the effects of cold acclimation (10d at 0 or 5°C) in non-diapausing and diapausing females. Our findings indicated that diapause decreased SCP significantly, while cold acclimation had no effect on the SCP except for non-diapausing females that were acclimated at 5°C. Acclimation at 5°C enhanced survival to acute cold stress in diapausing and non-diapausing females, with LT50 of −22.0 and −17.1°C, respectively. Altogether, our results indicate that T. urticae is a chill tolerant species, and that diapause and cold acclimation elevate cold hardiness in this species.