Evaluation of trapping methods for monitoring grain chinch bug in deciduous fruit orchards

Grain chinch bug (GCB) Macchiademus diplopterus is endemic to the Western Cape and as such is classified as a quarantine pest.  It is a pest of wheat and moves into orchards when the wheat is harvested, looking for overwintering sites.

The aim of this project was to evaluate trapping methods for the development of a practical method to monitor the time of dispersion of GCB from wheat fields into fruit orchards.  Various constituents of the alarm pheromone of GCB were tested in activity-meter experiments to determine whether the bugs were attracted (or repelled) to the pheromones.  The constituents tested were hexenal, tridecane, (E)-2-octenal, trans-2- octenyl acetate, trans-4-oxo-2-octenol, trans-2-hexenyl acetate and trans-2-hexenal.  Different coloured sticky traps were evaluated during two years to determine if GCB are attracted to specific colours.  The colours tested were yellow, black, brown, red, white and clear.  Eight orchards in the Ceres area were monitored using cardboard bands to assess whether this is a good method to assess fruit infestation with.

• Neither (E)-2-octenal nor Tridecane showed any marked response in the Chinch bugs during estivation, even if their period of highest activity (between 15:30 and 19:00) only is taken into account. Hexenal appears to have killed most of the bugs.  When bugs were active, only Tridecane and crushed bugs showed a significant repellent response, although much variation was found in the data.  This indicates that a more sensitive method is required to test these pheromones.
• No significant differences were found between sticky trap catches on different coloured boards and clear boards, indicating that these trap catches were due to the bugs flying onto the boards accidentally. In addition, not all the peaks that were monitored using cardboard bands were monitored on the sticky traps and it is believed that coloured sticky traps are therefore not a suitable method for monitoring GCB.
• Correlations between bugs caught in cardboard bands and bugs caught in fruit were poor, indicating that this is not a suitable method to assess fruit damage with.