Effects of prolonged exposure to cold on the spontaneous activity of two different types of filiform sensilla in Pyrrhocoris apterus.

We recorded the spontaneous activity of T₁ and T₂ filiform sensilla from October to May in Pyrrhocoris apterus acclimatized to outdoor conditions. The aim of the study was to determine how prolonged exposure to cold affects two closely related mechanosensitive sensilla. We recorded the activity at seven temperatures from 5 to 35 °C. In both sensilla types the activity level was reduced during winter, which correlated to changes in acclimatization temperature (r = 0.7), the reduction was greater at high recording temperatures, and the effects of exposure to cold were reversed by transferring the animals indoors. However, T₁ activity always increased monotonically, if the recording temperature was increased from 5 to 35 °C, whereas T₂ activity in cold-acclimatized animals increased to temperatures between 20 and 30 °C and then started decreasing. As a result, the temperature sensitivity of the activity was reduced more profoundly in T₂ sensilla (in T₂ Q₁₀ was reduced from 3.5 in October to 1.4 in January, whereas in T₁ it was reduced from 2.5 to 2.2). In conclusion, we have shown that prolonged exposure to cold does affect filiform sensilla; however, the effect is significantly different in the two sensilla types.