Unwelcome tourists

2 non-native stink bugs prompt questions about treatment thresholds, spray timings in Florida rice.

• By Vicky Boyd,
Editor •

matthew vanweelden

UF/IFAS faculty member Matthew VanWeelden — photo by Tyler Jones, UF/IFAS

Since it was first confirmed about 13 years ago, an exotic rice stink bug from the Caribbean and Central and South America has increased in abundance and is now the most common stink bug in Florida rice fields.

What the new species’ expansion means for grain stage susceptibility, existing treatment thresholds and insecticide timings are topics that Matthew VanWeelden, a faculty member with University of Florida Institute of Food and Agricultural Sciences, is currently pursuing.

With little information about the newcomer’s potential geographic distribution, he has suggested fellow rice entomologists survey for it, as well as another exotic rice stink bug species confirmed in Florida, in their states.

Two exotic stink bugs

o pugnax

Oebalus pugnax, the native rice stink bug — photos by Matthew VanWeelden, UF/IFAS

Oebalus pugnax, the scientific name for the native rice stink bug, is an annual pest of rice fields throughout the Mid-South and South.

In 1994, UF/IFAS researchers confirmed another species, O. ypsilongriseus, in Florida rice fields. It is a well-known pest of South American rice fields.

In 2007, UF/IFAS entomologists Ron Cherry and Gregg Nuessly confirmed a third rice stink bug species, O. insularis. This one is native to the Caribbean islands, Central America and South America.

At first glance, all three rice stink bugs appear similar, depending on natural color and marking variations. To help farmers and consultants differentiate the three, VanWeelden plans to produce a simple identification sheet they can keep in their trucks and use when scouting.

During 2008 and 2009, Cherry and Nuessly surveyed eight rice fields each year and found O. pugnax comprised roughly 54% of all catches, O. insularis, 20% and O. ypsilongriseus, 18%. Two other stink bug species that belonged to a different genus and were likely not rice pests accounted for the remainder of the catches.

o. ypsilongriseus

O. ypsilongriseus, a non-native rice stink bug from South America

The data showed both invasive Oebalus stink bug species were widespread in the region, according to the researchers.

2017 and 2018 surveys

During the past 10 years, Florida’s rice acreage has almost doubled to about 26,000 acres this season. Rice is mostly grown as a rotational crop as the flooded fields help reduce oxidation of the region’s highly organic peat soils and aid control of soil arthropod pests, such as wireworms.

In 2017 and 2018, VanWeelden surveyed the commercial rice acres and adjacent grassy weeds within the Everglades Agricultural Area. Located along the south and southeast shores of Lake Okeechobee, the EAA sits partly in Palm Beach County and hosts nearly all of the state’s rice production.

He took three 50-sweep samples each of the rice and of adjacent non-crop host plants that included 13 species of grassy weeds.

Diamond is the most popular rice variety grown in the EAA, with a much smaller acreage of Cheniere. Samples were collected at three sampling periods at up to eight locations per year.

O. insularis

O. insularis, an exotic rice stink bug native to the Caribbean islands, Central America and South America.

In a shift, O. insularis comprised 61.7% of samples collected in 2018, a two- to three-fold increase over 2007 and 2008 surveys, VanWeelden says. In addition, the exotic species took over from the native O. pugnax as the most abundant rice stink bug species in the state.

He says he doesn’t know why O. insularis has become more abundant and what the population shift means to the region’s rice producers.
“All of our thresholds for spraying are based on O. pugnax, and we don’t know if O. insularis’ feeding behavior is the same. Previously we had assumed they were feeding in the same way.”

During the 2019 season, VanWeelden established a caged feeding trial on the Diamond rice variety at the Everglades Research and Education Center near Belle Glade to begin to answer that. The trial looked at three stink bug species, three stink bug densities and three grain development stages.

Because of the complexity of the research, he says he’s still reviewing preliminary data from 2019. VanWeelden had hoped to repeat the trial this season, but that may be put on hold because of COVID-19 restrictions. If he isn’t able to plant the trial by May, he says he’ll have to forego it this season and try again in 2021.

VanWeelden also had hoped to survey non-crop hosts in other parts of Florida this year to determine the distribution of both exotic rice stink bug species.

“We don’t know about the presence of the other two species outside of the EAA area,” he says. “I don’t know if they’re up in different parts of the state.”

Surveying other states

stink bug feeding studies

UF/IFAS faculty member Matthew VanWeelden is conducting feeding trials with three stink bug species to determine whether current treatment thresholds may need to be changed.

Because of VanWeelden’s research, the Texas Rice Research Foundation provided funding this season to Mo Way to conduct a survey of rice stink bug species in the state.

“Those are exotics, so it’s time to take a look,” says Way, a Texas AgriLife Research entomologist based at the Beaumont Rice Research Station. He plans to examine rice stink bugs in both the Texas main and ratoon crops.

To help with sampling, Way hopes to enlist a number of consultants who walk rice fields west of Houston.

As they sweep fields, Way has asked them to put the rice stink bugs they’ve collected from their nets into plastic bags and freeze them for later pick-up. The consultants also will label the bags as to the field location, rice growth stage and rice variety.

“We’ll have a lot more to ID, and the samples will be bigger,” Way says, adding he will sweep rice fields east of Houston.

Mississippi State University Extension entomologist Jeff Gore says he also plans to conduct surveys this year to determine whether one or both of the exotic rice stink bugs have migrated west to his state.

University of Arkansas entomologists don’t plan to conduct a separate survey looking at other possible stink bug species, says Extension entomologist Nick Bateman. But they are collecting samples to send to colleagues on the university’s Fayetteville campus to examine for genetic diversity.

“We haven’t seen different species of rice stink bugs, but we have seen quite a bit of variation in rice stink bugs,” he says. “We haven’t been able to document the other two species.”