Western Ash Plat Bug – Tropidosteptes pacificus

Western Ash Plat Bug – Tropidosteptes pacificus

Common Name: Western Ash Plat Bug

Latin Name:  Tropidosteptes pacificus


  • The ash plant bugs are oval.
  • Nymphs vary up to the 1/8-inch length. Adults can reach a length of 1/4-inch.
  • Nymphs resemble huge, mobile aphids and range in colour from pale yellow to red to brown or black.
  • Adults are thinner than nymphs and have wings that cover their abdomens.
  • Nymphs and adults excrete tiny, black sticky droppings on the underside of afflicted leaves.

Damages caused by Western Ash Plat Bug:

Adults and nymphs feed and suck fluids from ash flowers, leaves, seeds, and twigs. Their visible damage is mainly restricted to leaf bleaching or stippling, as well as black faeces patches on leaves. Extreme infestations might cause trees to be defoliated prematurely. However, significant ash defoliation is more typically due to factors such as an anthracnose infection or unsuitable soil moisture, such as drought stress. If ash trees become highly infected and defoliated, the bugs may move on to feast on surrounding plants.

 Life history and habits:

Every year, there are two generations of ash plant bugs. The eggs hatch in the spring, just as the ash leaves begin to grow. In June, first-generation adults appear. They then mate and lay their eggs on the leaf midribs. Nymphs hatch from the eggs by July or August and grow into second-generation adults. Adults of the second generation mate and lay their eggs on twigs, bud scales, and other sheltered areas of the bark. These eggs survive the winter and hatch in the spring. Adults of the second generation are active until the first heavy frost. While the second generation of ash plant bugs is more active, the first generation causes greater leaf damage. Young leaves that develop in the spring are particularly vulnerable to plant-insect saliva.