Ash plant bugs—Tropidosteptes spp.
Tropidosteptes illitus and T. pacificus (family Miridae) feed on Fraxinus species mostly in the interior valleys of California. Tropidosteptes pacificus is sometimes called Pacific ash plant bug.
Tropidosteptes adults and nymphs are ovate and adults are about 1/5 inch long. Tropidosteptes illitus nymphs are light brown and adults are yellow and black or brown. Tropidosteptes pacificus nymphs are green with black spots and adults are brown or green.
Ash plant bugs develop through three life stages: egg, nymph, and adult. Overwintering is as eggs in twig bark. In February or March the nymphs emerge and feed until they mature in April or May. The adults feed mostly during June to July when the females lay eggs in leaf petioles or along the midribs or in twig bark. Ash plant bugs have one or two generations per year.
The nymphs and adults feed on and suck juices from ash flowers, leaves, seeds, and twigs. Their obvious damage is usually limited to leaf bleaching or stippling and dark spots of excrement on foliage. Extreme infestations can prematurely defoliate trees. However, severe defoliation of ash is more often due to causes such as an anthracnose infection or inappropriate soil moisture, such as drought stress. If ash trees become heavily infested and defoliated, the bugs may move to feed on other plants nearby.
Damage is rarely severe enough to cause defoliation or warrant control actions. If trees were defoliated the previous season and this was definitely known to have been caused by plant bugs and not other more common causes of defoliation, then relatively small trees can be sprayed with insecticides. Use horticultural oil or insecticidal soap in the spring to thoroughly cover leaf undersides infested with bug nymphs. Alternatively in late winter or early spring, soil around the base of the trunk can be drenched with a systemic insecticide, such as imidacloprid as directed on product labels.
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
Bleached specks (stippling) from feeding of ash plant bugs.
Brown adults, green nymphs, and varnishlike excrement of Pacific ash plant bug.
Adult Pacific ash plant bug.