The brown marmorated stinkbug is an invader that, when it arrives, can devastate crops. It has a hankering for orchard fruits and nuts, but other crops are targets as well, with a list of more than 100 plant targets.

One answer for this invasive species is the samurai wasp — Trissolcus japonicas — a tiny insect that hunts for the egg masses of brown marmorated stinkbugs and lays an egg inside each egg mass. With 28 eggs in a cluster, that's the potential for 28 more wasps. The parasitic wasp develops inside the egg, effectively killing the stinkbug. Then it chews its way out.

The brown marmorated stinkbug (BMS) showed up in Oregon in 2004, and while that state's economic impact has not been measured, the pest has caused significant damage in other parts of the country. The damage done by the stinkbug makes discovery of the wasp more important, according to David Lowenstein, an Oregon State University Extension Service entomologist.

BREAKING FREE: Once the stinkbug eggs have been parasitized, the samurai wasp chews its way out, leaving a jagged hole and stopping the stinkbug from surviving. (Photo by Oregon State University)

So far, tests to determine the success of the samurai wasp against the invasive stinkbugs have been positive, Lowenstein reports. He is lead author on a guide to identifying the samurai wasp.

He explains that as a biological pest, the wasp is a better way to control the BMS, which reduces the need for chemicals. Those chemicals are only somewhat effective, and the wasp is a specialist, Lowenstein says. "It doesn't lay eggs in other insect eggs — except those of other stinkbugs."

The shield-shaped stinkbugs give off a distinctive odor when they're crushed. "They move from wild host plants to our gardens, and then in large amounts into our homes [to overwinter]," says Vaughn Walton, an OSU Extension entomologist. "That's when people really get upset. Bugs inside freak people out."

THE TARGET: The brown marmorated stinkbug (shown here) is a growing pest problem in a number of crops with few predators. The samurai wasp may be the answer. (Photo by Gary Bernon, USDA APHIS, Bugwood.org)

Beyond chemical control
Control is also difficult. Research has shown that pesticides are only a short-term solution, and can kill the beneficial samurai wasp. Walton explains that the BMS can be distinguished from other stinkbugs by the bands on their antennae. In spring, adults start eating and laying eggs on the undersides of leaves. Within a week, eggs hatch into immature bugs and eventually adults, and the process starts again. The bug could reproduce up to three times a year depending on conditions.

Native to East Asia, the wasp has the same range as the BMS, so it's a natural enemy and probably hitched a ride on a ship. Scientists at OSU were already rearing and studying the beneficial insect in the lab when it was found last year in 11 areas in the Willamette Valley, including several in Portland. Since none had been released from the lab, the discovery was significant.

This summer, entomologist Lowenstein and other researchers will revisit those areas and some nearby to see if the wasp survived the winter. "Some natural enemy controls do great in the lab, but don't perform as well in the field," Lowenstein says. "But the fact that it's already widespread across Portland is a positive sign that it can withstand conditions in Oregon."

The public can have a role in samurai wasp research by collecting possible BMS egg masses and reporting them to Lowenstein on a form at the Wiman Lab website. You can also find more information on that site, with tips and photos to help with identification. One trick is to look for black eggs, which means they've been parasitized. Once the wasps emerge, there will be irregular holes. Taking photos is encouraged.

Source: Oregon State University