Age related mating behaviour and bioassay of the synthetic sex pheromone of the spotted stem borer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae)

Abstract

The influence of age on the mating behaviour of Chilo partellus (Swinhoe) was investigated. The observations on the behaviour of 0-, 1-, and 3-day-old months were carried out to ascertain if any changes occurred relative to age in attractiveness of the females and in the responsiveness of the males. The results showed that males were more attracted to 0-day old females than to 3-day old ones. No difference in attractiveness was found between 0- and 1-day old females. 0-day old males were found to have a significantly lower responsiveness to the females than both 1- and 3-day old ones. However, although 3-day old males were more responsive than 1-day old ones, this difference was not found to be significant.

Observations of the mating behaviour of the moths showed that there were quantitative differences in the behaviour of 0-day old males and 3-day old ones. 0-day old males were found to spend the largest proportion of the time passive and only very few of them copulated by the end of the observation period. On the other hand, 3-day old males spent a relatively smaller proportion of the time passive and most of them had mated by the end of the observation period. No significant differences were detected between the behaviour of the laboratory reared and the field collected insects.

The effect of proximity of release points of the two pheromone components (Z)-11-hexadecenal and (Z)-11-hexadecen-1-ol of the female moth were investigated. Separating the dispensers of the two components by a mere 3 cm resulted in a significant change in the male behaviour and a decrease in the bait performance as compared to the dispensers with the two components dispensed close to each other.

A study to establish the effect of polyvinyl chloride (PVC) on the response of the male C. partellus to the synthetic blend of the sex pheromone of the female showed that PVC does not inhibit male response to the pheromone. It was found, however, that the PVC dispenser loaded with the alcohol was inferior in its performance to the filter paper dispenser loaded with the same and this could possibly be attributed to a lower release rate of the alcohol by PVC.