Abstract: Spontaneous discharges of action potentials (AP) of neuromuscular preparations in the leg and fore- or mid-gut of the Colorado potato beetle, Leptinotarsa decemlineata were recorded in situ under the treatment of oral injection of Cry3A toxin and permethrin insecticide. Both of the two chemicals exhibited rather specific electrophysiological symptoms in the preparations: they evoked groups of action potentials with highly increased frequencies in the early stage, and led to long period of interspike resting, the duration of which increased as intoxication proceeded. Permethrin typically caused extremely high frequency discharges (overshooting) in the leg preparations and very short interspike resting periods, but the Cry3A toxin only exhibited these effects in the gut preparations. Also Cry3A toxin increased excretion dramatically and decreased feeding of the treated beetles. These results indicated that the nerve muscle system in the gut appears to be much more sensitive to Cry3A toxin than that in the leg and the primary neurotoxic or myotoxic action of Cry3A, causing a disturbance of the gut activity, is an important mechanism of its insect poisoning consequence.

Key words: Leptinotarsa decemlineata, Cry3A toxin, permethrin, electrophysiology