Survivor: Winter Insects

Two factors indicate an insect’s ability to survive the winter: their biological adaptations to cold and a hospitable place to settle in to keep from freezing. If they hunker down successfully in your field, they’ll be in place to start feeding and breeding as soon as seeds are in the ground.

Because insects are unable to create their own body heat, three primary types of adaptation allow them to emerge in spring fields for another season: freeze avoidance, freeze tolerance, and “insect hibernation” or diapause.

Freeze-avoidant insects produce antifreeze proteins in their bodies as the cold moves in, allowing them to acclimate to the cold and survive sharp drops in temperature. Freeze-tolerant insects produce nucleating proteins that accumulate in their hemolymph — a fluid similar to blood in humans — which cause ice crystals to form in the hemolymph instead of the cells, where they would be lethal to the insect.

Diapause is a metabolic slow-down, regulated by hormones and genetically triggered to take place during a particular life stage. It’s effectively a state of suspended animation, during which growth and development slow and the insect’s resistance to extreme conditions increases. Extended diapause is what allows Northern corn rootworm to beat the corn-bean rotation by “sleeping” until corn is on the menu again.

Fight Back Against Threatening Insects

For soil dwelling insects, the most dangerous phase of development is often the larval stage when insects are hungry and preparing to pupate. Soil boring insects feed on plant roots or, in the case of cutworms, tender plant stems. In addition to feeding damage, the insects can spread disease through the crop as they move from plant to plant. They’re also most vulnerable to pesticides as larvae.

Since growers can’t count on the cold to kill off all the insects in their fields, integrated pest management (IPM) is a grower’s best approach against those that survive, according to Matt Geiger, agronomy service representative for Syngenta in south central Illinois.

“You should do multiple things to control your pests, not just one,” Geiger says. “You want to manage the vegetation in and around your fields and use good traits in conjunction with crop protection and seed treatments.”

A good time to scout is after harvest, when egg masses on dead plants, tree bark, and other sheltered locations are easier to see. Cultural controls against overwintering insects include tillage, which can disrupt habitats by incorporating field residue into the soil, destroying insect eggs laid in field stubble, and compacting the dirt, potentially crushing or trapping insects in the ground. Insects unearthed by tillage are also more likely to be exposed to predators or sudden severe weather they can’t bounce back from.

Crop rotation is another way to separate a pest from its crop of choice, as many corn growers learned after battling corn rootworm. In addition to depriving them of their food source, rotation can subject the insects to conditions they aren’t equipped for.

On the chemistry side, Geiger says clean fields are crucial even in cold weather, since insects, including cutworm moths, mate and lay eggs from early spring to late fall.

“In corn, you really don’t want to let a bunch of weeds go in the winter because cutworms could lay eggs in the weeds or potentially in a cover crop,” he says, noting that vegetation left in a field also serves as insulation for the insects beneath it.

“That insect can clip corn plants off at the ground if you don’t use traited corn. You should also have an insecticide like Warrior II with Zeon Technology^® mixed with your corn residual herbicide pass.”

“When cutworms crawl across the ground, that insecticide will absorb into their bellies and kill them before they can clip the plants. Every farmer should be using a soil-applied insecticide if cutworms are a risk for their geography.”

On the seed side, Geiger says, DuracadeViptera™ corn trait stacks feature a unique mode of action that controls corn rootworm differently than others on the market along with offering protection against cutworms, earworms and rootworms.

“The most devastating insects are overwintering in the soil — corn rootworm, wireworm — those are big problems,” Geiger says. “If you’ve got those, you need to have an IPM strategy, for sure.”