Fig. 5. Effect of pymetrozine on the resistance reflex in the middle leg femur–tibia joint of the stick insect Cuniculina impigra. (A) Tibia position (middle trace) in response to sinusoidal stimulation of the femoral chordotonal organ (bottom trace; stimulus frequency 0.5 Hz; amplitude 400 µm, corresponding to 80° tibia movement; arrow indicates tibia extension and fCO elongation). Top trace shows a flexor tibiae electromyogram. Application of 10^–6 mol l^–1 (probably diluted before actually reaching the fCO) pymetrozine was just before the beginning of the sample shown. (B,C) In this animal, movement response declined slowly within 1–2 mins of pymetrozine application. This allowed measurement at two stimulus frequencies (0.02 and 0.05 Hz; filled circles). The modified Bode diagram plots response amplitude (B) and phase lag (C) versus stimulus frequency (diamonds, before pymetrozine). Note the decrease in response amplitude and unaltered phase lag after pymetrozine application. Arrow in B indicates stimulus situation depicted in A (0.5 Hz, different animal).