Utah Pests News Fall 2014


First Report of Elm Seed Bug in Utah


In July 2014, the UPPDL received multiple submissions of a small, brown and black insect. We identified it, with confirmation from USDA APHIS, as elm seed bug (Arocatus melanocephalus), marking its first official appearance in the state. A native of Europe, the elm seed bug was first identified in the U.S. in Idaho in 2012 and then in Oregon in 2013. While the Utah sample submissions came from Salt Lake County, I also collected and identified this insect in Cache County around the same time. It is possible that the elm seed bug is already widely distributed along the Wasatch Front.

As a member of the family Lygaeidae, or the seed bugs, this insect feeds primarily on elm seeds, but can be found on other trees. In northern Italy, this insect has become a major nuisance pest, entering homes and buildings by the thousands, similar to the boxelder bug in Utah. Unlike boxelder bug, elm seed bugs can emit a pungent smell from scent glands, similar to bitter almonds.

The specifics of the elm seed bug life cycle in the U.S. are only generally understood. In northern Italy (Turin ~ 45°N and Modena ~ 44°N; Salt Lake City ~ 40°N), the insects overwinter as adults and begin to move from overwintering sites to host trees in March. Eggs are laid starting in early May on elm fruits (samara) and young nymphs emerge in mid-to-late May. The nymphs progress through 5 growth stages before becoming a winged adult. There can be many overlapping life stages present during the summer, but in Italy, the insects have one generation per year. Invasions of buildings have occurred anytime between late May and late September and were seen to coincide with peak summer temperatures.

Control of elm seed bug with insecticides may be difficult due to their mobile behavior. Italian entomologists report that city governments attempted control with etofenprox, pyrethrum, and rotenone, but only etofenprox showed efficacy. In Italy, insecticides are most effectively applied to host trees when immature stages are present, beginning in early May.

Unfortunately, adult emergence dates, egg laying, and egg hatch are not known in Utah. Proper spray timing for elm seed bug in Utah should be accurately timed to coincide with the presence of the nymph stages for greatest results. Adults may start appearing in March and their nymphs, in April and May.

Pest-proofing homes and buildings is the best tactic to deal with nuisance pests like the new elm seed bug, just as it is for the boxelder bug. The general exclusion techniques found in the USU Boxelder Bug fact sheet will help provide relief from this new pest. Where swarms are found, such as on warm exterior walls, the bugs can be vacuumed up into soapy water to quickly reduce large populations. More information on the elm seed bug and its control can be found in the fact sheet from the Idaho State Department of Agriculture.

- Ryan Davis, Arthropod Diagnostician and School IPM Associate



Ferracini, C. and A. Alma. 2008. Arocatus melanocephalus: a hemipteran pest on elm in the urban environment. Bulletin of Insectology, 61(1): 193-194.

Maistrello, L., L. Lombroso, E. Pedroni, A. Reggiani, and S. Vanin. 2006. Summer raids of Arocatus melanocephalus (Heteroptera, Lygaeidae) in urban buildings in Northern Italy: Is climate change to blame? Journal of Thermal Biology, 31(8): 594-598.

Idaho State Department of Agriculture. 2013. Elm seed bug, Arocatus melanocephalus: an exotic invasive pest new to the U.S. Fact sheet: 4pp.


Featured Picture of the Quarter

featured pic

Squash bugs are a perennial pest problem across Utah. The feather-legged fly (Trichopoda pennipes), a member of the parasitic fly family, Tachinidae, is one of just a few natural enemies that plays a small role in reducing squash bug (and stink bug) populations. The adult female lays several small whitish eggs on the outside of the host body. When the eggs hatch, the larvae burrow inside the host to feed on its contents. During this time, the host still lives, but does not reproduce. The larvae pupate inside the host and emerge as adult flies, at which time the host insect dies.

-Image by Bonnie Bunn, Vegetable IPM Associate