Development of monitoring methods and optimisation of a pheromone lure for the grain chinch bug, Macchiademus diplopterus

We investigated the chemical ecology and orientation behaviour of shelter-seeking grain chinch bugs, Macchiademus diplopterus, to evaluate the use of pheromones and profiles in monitoring and trapping methods for grain chinch bugs.

Headspace volatile compounds were identified from active bugs through gas chromatography-mass spectrometry analysis. The efficacy of synthetic lures using previously identified aggregation pheromone components, and sex pheromone volatile components (identified in present study) was studied in combination with modified traps using rubber septa dispensers in field trials. Also, behavioural responses of grain chinch bugs to visual objects (shapes – rectangle, circle, triangle and square; and colours – red, black, green and yellow) were carried out under laboratory conditions.

There was no significant difference (P > 0.05) between insects caught in the sex pheromone baited traps and the aggregation pheromone baited traps. Traps caught low numbers of bugs compared to the level of orchard infestation indicated by the amount of bugs that were found sheltering in corrugated cardboard bands tied around tree trunks. The corrugated cardboard bands showed a significant difference in the number of bugs sheltering between bands placed at bottom and top positions on the trees. More bugs were found in bottom bands. Behavioural responses of grain chinch bugs to different shapes presented in their visual space indicated that there was a significant difference (P = 0.0001) in the choice of shape. Vertical/upright rectangular shapes had the highest number of grain chinch bug visits. Grain chinch bugs responded to upright rectangles of different colours. Black and red rectangles were not significantly different (P > 0.05) from each other but were both significantly different (P = 0.0001) from green and yellow rectangles.

The study has provided new information on the constituents of pheromones produced by grain chinch bugs, but use of these pheromones as lures in trapping systems for the grain chinch bug requires additional work. Grain chinch bugs have a preference with regard to the shape and colour of profiles in its field of view. This preference must be taken into consideration and used in combination with effective lures, when developing traps to attract grain chinch bugs.