Multiple mechanisms generate the resting activity of filiform sensilla in the firebug (<Emphasis Type="Italic">Pyrrhocoris apterus</Emphasis> L.; Heteroptera)

The resting activity was studied in filiform sensilla of the firebug (Pyrrhocoris apterus). Three functional types (T₁, T₂ and T₃) were detected on the abdomen. A resting discharge of nerve impulses is present in all—always in types T₁ and T₂ and occasionally in type T₃. In T₁ the mean rate is 57, in T₂ 3.3 and in T₃ 0.5 imp/s. Shortening the hair length had a negligible effect on the resting discharge, which indicates an intrinsic origin. The resting activity is highly temperature dependent. In T₁, the activation energy was 56.8, in T₂ 84 and in T₃ 61.4 kJ/mol (Q ₁₀: 2.27, 5.6 and 5.5, respectively). Such values are typical for mechano-transduction, suggesting the involvement of the transduction mechanism itself. The destruction of the hair base in T₁ caused halving of the original discharge rate and shifted the discharge to a regular interval mode. The activation energy decreased to 38 kJ/mol. The destruction of the hair bases in T₂ and T₃ completely abolished the discharge. It appears that at least two mechanisms are involved in the generation of the resting activity in T₁ units while only one can be assumed in case of T₂ and T₃.