Three seconds. That is all the time it takes for a Japanese beetle to land on a pyrethroid net, pick up the toxin and die.
The pyrethroid net is like a roach motel used by homeowners. “You’re going to try to attract a specific pest to a specific area and then kill it there,” explains Kevin Rice, University of Missouri Extension entomologist.
Rice, along with MU graduate student Kelsey Benthall, is studying and developing a new net trap set along soybean field borders to attract and kill Japanese beetles. It is treated with two lures — one contains aggregation pheromone that attracts males and females, the other attracts as a feeding site.
Benthall set up one 76-meter net, not even the entire length of the MU soybean research field. She also had a control strip without a net. On it, she sprayed two applications of pyrethroid throughout the growing season, lower than most field applications for this beetle in Missouri.
From June to October, Benthall went into the field to see the effect of the treated nets. She conducted pest sweep samples from five different soybean rows — two, four, six, eight and 20 — and collected pollinators. Then she scored defoliation. At the end of the season, Benthall collected seed to assess any damage or discoloration.
Results are in
There were mounds of dead beetles at the bottom of the nets. “It actually smelled like dead deer carcasses,” Rice says. “It was killing that many beetles. It was that effective.”
Still, the study found a very low population of defoliation because of the reduced presence of defoliator pests and Japanese beetles. Compared to the control strip, the area with treated nets had similar defoliation with no statistical difference. Rice adds the numbers are nowhere near the threshold in which farmers would spray.
“The basic take-home here is that it looks like the nets are providing equivalent protection to two sprays of insecticides throughout the season,” he says.
EDGE OF PROTECTION: The pyrethroid net system is positioned along the soybean field edge. The nets aren't affected by rain or ultraviolet light and last one year. University of Missouri researchers continue to look at size, placement and potency of these nets as a future tool to manage Japanese beetles.
A surprise from the study was reduced seed damage and increased seed quality with the nets in place. Rice admits he thought these two factors would be similar to the control field. So, the researcher and his graduate student did a little digging, and they found an answer in the sweep nets.
In the field with the pyrethroid net was a higher population of predatory bugs such as wasps that naturally keep stinkbug populations in check. “So, in the spray plots, you’re killing wasps, so there is an increase in stinkbugs later in the season because the field no longer has any natural enemies there,” Rice explains.
Using the pyrethroid nets all season long allows for control of the Japanese beetle while not harming good bugs that keep bad bugs at bay. Soybeans from the field with the net saw 10% less seed damage than the sprayed field.
More work ahead
Missouri is at the invasion front for Japanese beetles. “We have higher populations in Missouri than they do on the East Coast,” Rice says. And while the USDA released a parasitoid wasp there, it has not yet made its way to the Midwest. So, Japanese beetle populations will continue to rise until it arrives.
Meanwhile, farmers need to find an alternative to spraying. The university will continue to the study looking at dosage, size and placement of nets around fields.
The pyrethroid net allows farmers to kill adult beetles, improve soybean quality, reduce chemical applications, and preserve predators and pollinators. “And you're also reducing the likelihood of pesticide resistance with increased sprays,” Rice adds.
The pyrethroid net may not be the silver bullet to solving the Japanese beetle problem, but Rice says, “It might be a bullet,” and it may work even better under higher populations.