BUG DAMAGE IN NEW-ZEALAND WHEAT-GRAIN - THE ROLE OF VARIOUS HETEROPTEROUS INSECTS

Certain heteropterous insects (true bugs) in New Zealand deposit salivary enzymes into immature wheat grain while feeding. These enzymes survive in harvested wheat, destroy gluten structure in dough, and cause poor quality bread. This study investigates what insect is responsible for bug-damaged wheat. The following field-collected insect species were caged on wheat at the watery ripe growth stage: Nysius huttoni, Rhypodes sp., Stenotus binotatus, Calocoris norvegicus, Sidnia kinbergi, and Dictyotus caenosus. All the insects produced visible signs of damage on kernels and reduced kernel weight, but only wheat damaged by N. huttoni and S. binotatus had sufficiently high levels of pH 9 active, gluten-degrading enzyme to cause poor quality bread. However, the electrophoretic patterns of protein subunits from degraded gluten and the characteristics of bug damage in bread were different for these two insect.s. Also, the appearances of the damaged kernels and levels of alpha-amylase were clearly different in the two samples. Only wheat damaged by N. huttoni showed all the characteristics of naturally bug-damaged wheat harvested and tested in New Zealand during the last decade.