ABSTRACT Essential oil from lovage (Levisticum officinale Koch.) is a potential low-risk insecticide containing monoterpenes. It was tested with increasing concentrations in saline for neural effects on the autonomous ventilatory rhythm of an isolated Abdominal Ganglion (AG5) which supplies the fifth abdominal segment of Locusta migratoria (Forskal). The inhibition by lovage oil was compared with that of its main components, the enantiomers of limonene (D- and L-limonene). All substances depressed the persistent ventilatory motor output: the concentration-dependent reduction of the neural activity was measured with the average Action Potential (AP) frequency of the inspiratory motoneurons in the median nerve. Occasionally the motor output could switch from bursting activity with more or less gradual transients to continuous tonic firing. Recovery of the AG5 in pure saline after highest concentrations had been applied was gradual but the ventilatory output never returned completely to the pre-application level of motor activity. The strong short-term neurotoxic effects of the limonene enantiomeres in the insect CNS are followed by a moderate long term neural depression.