The Good Virus: A Bioinsecticide Helps Farmers Control Caterpillar Pests

10/19/2021 | 10:12 AM CDT

Progressive Farmer

By  Emily Unglesbee , DTN Staff ReporterConnect with Emily: @Emily_Unglesbee

ROCKVILLE, Md. (DTN) — Frank Appleberry has a list of things to apply each spring to his crop fields in Tillar, Arkansas: preplant fertilizer, preemergence herbicides and oh, don’t forget the liquid blend of pulverized caterpillars, teeming with live viruses.

It sounds unconventional, but for a growing number of American farmers, this type of bioinsecticide is proving a regular and reliable tool to control Helicoverpa zea, the multi-crop pest known as soybean podworm, sorghum headworm, corn earworm and cotton bollworm.

These bioinsecticides are made from a strain of naturally occurring nuclear polyhedrosis viruses (NPVs), recently categorized as Group 31 insecticides. They are sprayed on row crop foliage like a normal insecticide. From there, things get a little gruesome, but only for the targeted caterpillar pests.

After ingesting the bioinsecticide, the caterpillar dies within a week, and the virus turns its corpse into a virus-replicating factory. The blackened, jelly-like remains of the worm overflow with more viruses, ready to infect more caterpillars, who in turn produce more virus. And so the cycle goes, until the caterpillar infestation abates and — without a host — the virus fades into the ecological background.

“It’s just part of what we do now in the spring,” explained Appleberry, who has replaced much of his onerous schedule of spraying soybeans at least every two weeks, with a single application of an NPV-based bioinsecticide called Heligen, around soybean bloom. “The first year we used it, we sprayed 1,150 acres and only had to come back with a pyrethroid for worms on about 200 acres,” he recalled.

These types of viruses are already circulating in nature and are not totally new to agriculture. University researchers dabbled with harnessing their insecticidal properties back in the 1970s, but they were largely supplanted by the advent of fast-acting synthetic insecticides, such as pyrethroids.

Now, a global biotech company, AgBiTech, has scaled up a commercial NPV product in the U.S., Heligen. It uses an NPV strain that targets H. zea (bollworm/earworm/podworm/headworm) and is registered for use in most row crops. AgBiTech also offers a suite of products registered globally to control other caterpillar pests, such as soybean looper (Chrysogen), armyworm (Fawligen), old world bollworm (Armigen), and a dual-virus product combining the H. zea and soybean looper strains (Surtivo). Other brands of NPVs also exist, but AgBiTech has made the largest inroads among American growers, university entomologists and farmers told DTN.

Amid growing insect resistance to insecticides and Bt, as well as interest in more eco-friendly farming practices, the success of NPVs has caught the attention of an even bigger player — Corteva Agriscience. This year, the company announced its plans to commercialize an NPV strain marketed under the brand name, Hearken, developed by a German company, Andermatt Biocontrol.

HARNESSING A FARMER-FRIENDLY VIRUS

AgBiTech prides itself on running what Chief Technology Officer Paula Marcon jokingly calls “a five-star hotel for caterpillars” at the company’s manufacturing facility in Fort Worth, Texas. No check-out required for these doomed guests, however, as the company infects the insects with their NPV strain of choice and then blends them into a smoothie-like liquid, ready for the sprayer.

“It’s a little brownish, like syrup and smells wonderful,” Marcon said. “And it’s well adapted to foliar applications.” Since the NPV cocktails contain living organisms, they do come with some special handling requirements. They can last many years in a freezer and several months at room temperature (under 77 degrees), but if they stay at temperatures well above 77 degrees for more than 36 hours, the products can start to break down. “That last mile to the field, you have to be careful,” said Marcon.

And since the viruses are protected by a protein coating that is degraded by highly alkaline environments — such as a caterpillar’s stomach — tank mixes need to stay below a pH of 8 to keep the virus alive, Marcon said. AgBiTech’s products, such as Heligen and Surtivo, can be tank mixed with other active ingredients, such as herbicides or fungicides, as long as the tank’s pH stays low enough, added Marcos Castro, AgBiTech’s vice president of sales and marketing.

Heligen requires a fairly low use rate, ranging from 1 to 2.5 ounces, depending on the crop, with costs landing around $5 to $6 per acre.