Apr 26, 2018

Oregon researchers find a native wasp with a taste for stink bugs

“The wasp outsmarted us,” Lowenstein says.

Astata unicolor is a soil-nesting wasp that hunts stink bugs to feed to its offspring. While many parasitoid wasp species target their hosts’ eggs, A. unicolor prefers late-instar nymphs and adults. When an adult female A. unicolor finds its stink bug prey, it paralyzes the stink bug with a sting, drags it off to its nest, and lays an egg on the immobilized victim, which then serves as a fresh food source for the wasp larva when it hatches.

Of special note, though, is the species of stink bug that Astata unicolor appears to like best: Halyomorpha halys, the invasive brown marmorated stink bug.

In a report published this month in the Annals of the Entomological Society of America, Lowenstein, a postdoctoral research associate at Oregon State University, and colleagues detail their observations of a small population of Astata unicolor wasps in a residential garden in Portland, Oregon, and discuss its potential as a native biological enemy of the brown marmorated stink bug.

A. unicolor grows to about 1 centimeter in length in adult form, with an orange or black abdomen. It tends to make its nests in hard-packed soil. Only a few previous studies have documented the species’ affinity for the brown marmorated stink bug, which Lowenstein attributes to the difficulty in studying it, noting that it is also both solitary and a fast flier.

In the course of their observations, Lowenstein’s team charted A. unicolor flying between July and September, and they witnessed it paralyzing another insect on 22 occasions. In 14 of those instances, the prey was the brown marmorated stink bug; the others included stink bug species Banasa dimidiata and Chlorochroa ligata as well as one western boxelder bug (Boisea rubrolineata). Lowenstein calls A. unicolor “a win-win for homeowners searching for a biocontrol agent that can attack two pests that congregate on the side of homes.”

As the brown marmorated stink bug (BMSB) reaches essentially full expansion across the continental United States, entomologists are striving to find biological enemies of the invasive pest, because chemical insecticides’ inefficient management has stymied most efforts to control it thus far. Currently, efforts are primarily focused on the small parasitoid samurai wasp (Trissolcus japonicus), which offers promise for its ability to be reared en masse in a laboratory and then deployed in the field.

However, “it remains too soon to tell how well Astata manage BMSB,” Lowenstein says. “Astata have specialized nesting requirements, which limit the types of places they are found. There are still gaps about the ideal habitat for Astata, and we can’t make recommendations about how to attract the wasp. It is possible that the wasp could nest in habitat adjacent to crops.”

Where A. unicolor and its Astata cousins occur naturally, though, there’s reason for hope. “Someone who finds an Astata wasp carrying a BMSB should be excited, since the Astata will collect multiple BMSB during the season and have a local impact,” Lowenstein says.

Lowenstein and co-authors Heather Andrews, Erica Rudolph, and Nik Wiman are working on a BMSB-management project in Oregon, headquartered at the OSU’s North Willamette Research and Extension Center. The study on A. unicolor was “a classic story of serendipity,” Lowenstein says, as Portland gardener Ed Sullivan (also a co-author on the article) noticed the wasps attacking BMSB in 2013 and contacted OSU’s extension service in 2016 after several events publicizing BMSB detection. He then welcomed the team of researchers to visit to observe the wasps over the next two summers.

“This paper is a success at showing the value of science outreach and working together with an interested gardener to gather information on an understudied wasp with economic importance,” Lowenstein says. “A group of individuals across all career stages – undergraduate, faculty research assistant, postdoc, faculty member – and member of the public worked on this paper.

– Entomological Society of America