Rhizoglyphus Robini , a Pest Mite of Saffron, is Unable to Resist Extracellular Ice Formation

The saffron mite, Rhizoglyphus robini Claparède (Acari, Astigmata: Acaridae), is one of the most important pests of saffron-producing regions in Iran. It causes yellowing and decreases saffron growth, and finally it destroys the bulbs. In this research, the cold tolerance and supercooling point (SCP) of the saffron mite were measured in three populations and two temperature regimes. Our results showed that the mean SCP of the saffron mite was approximately −14.6 °C without significant difference among the populations. On the contrary, acclimation of the mites significantly decreased their SCP to a mean of approximately −16.5 °C. Exposure of the mites for 24 h to 0 and −2.5 °C had no significant effect on the survival of the mites but when the mites were exposed to −5.0 °C for 24 h, survival of the three populations reached the lowest level of roughly 60%. By 24-h exposure to −7.5 °C, survival of the mites was almost negligible. As a large proportion of mortality was observed above the SCP, and LT 50 > SCP, it can be inferred that the saffron mite is likely a chill-susceptible species. This suggests that the saffron mite lacks the ability to withstand extracellular ice formation. Overall, the results of the current study suggest no significant physiological differences between populations of the saffron mite.