Confirmation that brown marmorated stink bug (BMSB) feeding on pistachio nuts causes kernel necrosis is not surprising, but it means growers could have to contend with another invasive species with the potential to cause economic damage.

Native stink bugs feeding on pistachio nuts are known to cause damage, UC Riverside (UCR) researcher Ricky Lara said, but the polyphagous and highly mobile BMSB poses different challenges in the agriculture industry.

Lara said field trials have demonstrated that chemical control alone for BMSB is not always an effective management strategy.

“These are highly mobile, voracious, and new to the pest complex,” Lara said. “They can disrupt the efficacy of existing pest management strategies.”

Concerted research efforts are underway to deliver cost effective BMSB integrated pest management in the U.S.

The UCR research is part of a nationwide USDA Specialty Crop Research Initiative-funded program to monitor and control BMSB. Funding from the California Department of Food and Agriculture’s (CDFA) Specialty Block Grant Program has also been crucial in advancing BMSB management research for the benefit of California stakeholders.

Lara said BMSB research in California is aimed at developing sustainable solutions including biological control for BMSB suppression.

Along with UC Extension entomology specialist Mark Hoddle and CDFA senior environmental research scientist Charlie Pickett, Lara is investigating the potential of a beneficial stink bug egg parasite - Trissolcus japonica, better known as the ‘samurai wasp’ - to provide natural BMSB control.

The samurai wasp was imported by USDA from Beijing, China for close study in a secure quarantine space. Beijing is part of the home range for BMSB.

Lara said the California research team is also evaluating the role of native stinkbug parasitoids for BMSB control.

BMSB caused severe economic damage to fruit crops on the East Coast in 2010 after arriving from Asia in the 1990s. More recently, the pest was found in Oregon and Washington in commercial orchards.

In California, reproducing populations have been found in nine counties, plus detections in 21 other counties, including Kern County.

The pest was found in a commercial peach orchard by UC Cooperative Extension researchers in Stanislaus County last year. So far, there are no confirmed reports of economic damage in peach or commercial nut crops. Lara said under laboratory conditions BMSB could feed on Kerman pistachios.

The adult BMSB has a typical stink bug ‘shield’ shape, but can be distinguished from native stink bugs of comparable color by the presence of white bands on antennae and legs, rounded shoulder, and a prominent light-dark banding pattern on the abdomen.

Eggs are barrel shaped, white to pale green, and laid as egg masses on leaves. Newly hatched nymphs can resemble other resident stink bugs so identification is much easier in adults.

Where BMSB are reproducing, adults aggregate in the fall and move to protected places, including human-made structures to overwinter. They become active in the spring when feeding.

After mating, the female lays eggs in clusters on plant material with at least one generation per year in California. In warmer areas two can be expected. Monitoring efforts are helping assess this part of BMSB ecology.

Lara said BMSB biological control research in California has two key natural enemy groups under consideration: resident predators-parasitoids associated with native stink bugs and the samurai wasp.

The samurai wasp was self-introduced into the U.S. from Asia where it naturally targets BMSB providing some BMSB control, she said. The wasp is not established in California, but Lara said that the aim of proactive safety testing done in quarantine at UC Riverside is to evaluate the risk of parasitism to non-target stink bugs established in California.

Similar efforts have been completed in other parts of the country under the guidance of USDA’s Agricultural Research Service.

Resident stinkbug egg parasitoids could also provide some control if they attack the first generation of BMSB eggs laid in the spring. California has at least 11 reported species of these beneficial insects.

Lara said field studies in Riverside, Los Angeles, and Sacramento counties have located BMSB egg masses attacked by native parasitoids. Results have been encouraging and promise to deliver sustainable pest management options for growers where BMSB is problematic. 

The California BMSB biological control program is supported by CDFA, USDA-ARS, UC Cooperative Extension, and commodity boards including the California Pistachio Research Board.