Multiple mechanisms generate the resting activity of filiform sensilla in the firebug (Pyrrhocoris apterus L.; Heteroptera).

The resting activity was studied in filiform sensilla of the firebug (Pyrrhocoris apterus). Three functional types (T(1), T(2) and T(3)) were detected on the abdomen. A resting discharge of nerve impulses is present in all-always in types T(1) and T(2) and occasionally in type T(3). In T(1) the mean rate is 57, in T(2) 3.3 and in T(3) 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 T(1), the activation energy was 56.8, in T(2) 84 and in T(3) 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 T(1) 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 T(2) and T(3) completely abolished the discharge. It appears that at least two mechanisms are involved in the generation of the resting activity in T(1) units while only one can be assumed in case of T(2) and T(3).