Aim: 

Morpho-functional data on the muscular arrangement and motoneurons activity within nerve pairs IV (N4) to VI (N6) emerging from the terminal abdominal ganglion (TAG) were correlated to the cyclic ovipositor extensions and retractions (calling behaviour) responsible for the pheromone release in the gypsy moth Lymantria dispar.

Methods: 

In whole 2–3 days old calling females the firing patterns displayed by nerves N4 to N6 was simultaneously recorded with extracellular suction electrodes and coupled with EMG recordings (A-M System differential amplifier) of the muscles involved in calling behaviour; the behavioural output associated with motor unit(s) activity was video-monitored. All data were analysed by means of pClamp 10.0.

Results: 

Several different pairs of abdominal muscles, mostly innervated by N5, were identified, while N6 was found to mainly innervate the oviductal tract. N4 appears to innnervate two muscle pairs only, both located in the abdominal wall. The spike trains of a number of motoneurons within both N4 and N5 were found to be time-related with changes in the relative position of the ovipositor, both in extension and retraction movements.

Conclusions: 

In the female gypsy moth the sex pheromone release is brought about by the squeezing action due to the turtleneck-like folding and unfolding of the ovipositor cuticle during the telescopic extensions and retractions of the ovipositor operated by a coordinated motor programme, which is mainly sustained by the activity of motoneurons projecting from the TAG via N4 and N5.