Insecticides: Migration Matters

PREDICTING an annual forecast for insecticide deployment in the Northern Hemisphere field crop growing season can only be as reliable as predicting weather forecasts around the world. No matter how tried-and-true data might appear, an unforeseen event can change everything. But the crop protection sector can still better prepare.

Many manufacturers offer transgenic and seed-coating alternatives to insecticides to stem pest outbreaks regardless of climate. But insect populations are fighting back, showing some immunity to these equalizers.


How one gauges the weather conditions for insect migrations determines not only which treatments are appropriate, but also when to use them. Take note of regional weather trends as they affect insect migration patterns.

If it sounds complicated, that’s because it is. “It’s really not possible to predict any outbreaks based upon weather trends that precede a growing season,” says Larry Bledsoe, research and extension entomologist at West Lafayette, Indiana-based Purdue University. “All you can do is offer an opinion or give your feeling. In the Midwestern US, it’s been very mild so far with little snowfall, and if the weather stays warm, then certain things will happen. But if it gets cold, the situation changes.”

Winter conditions mean far less than the timing of the weather breaking, he says. When things warm up and growing begins, insects get busy in the fields.

In the Midwestern US, look at prevailing trends coming out of the Gulf of Mexico. Insect populations in Louisiana and Mississippi are already increasing due to the warmer climate, hitching rides up to the northern US on early season storms.

Grant money and sponsorships are opening up research opportunities on weather trends and insect migration around the world.

In Illinois, Mike Sandstrom operates, which is sponsored by Monsanto. Sandstrom studied insect trap counts for 10 years in the food processing industry and developed a rich database, then crossed the data with weather trends to come up with the site. He hones in on weather patterns and the migration of corn earworm and Western bean cutworm populations in North America, and publishes daily forecasts on the site from May through September. Forecasts are offered along with three- to five-day outlooks.

“The key to studying migration is to make it proactive,” Sandstrom tells Farm Chemicals International. Plan ahead, noting that weather and heat units are very important factors in insect migration. “Certain conditions make it more possible for heavy migration of the corn earworm, for example, but if the growing season to the North isn’t in a susceptible growing stage, then there is no worry.”

Corn earworms tend to book their flights on winds preceding cold fronts, he explained. Southerly winds in North America generally precede a cold front. Insects migrate in the atmosphere, where winds can reach 100 miles per hour – then a cold front or storm brings them down to crops. If crops are in a growing phase and susceptible, growers experience migratory outbreaks.

Dominic Reisig, assistant professor and extension specialist at the Department of Entomology at North Carolina State University, is operating on a grant and tracking insects in North America. “We are in a strong La Niña weather pattern in the Southeast US. That means warmer and drier than usual conditions,” he says.

For wheat, warmer spring conditions favor cereal leaf beetle emergence and development. In corn, growers have seen increasing issues with sugarcane beetles. “I expect this pest to be an issue this year as well,” Reisig says.

“For cotton, the warmer winter may mean better overwinter survival of stink bugs. Stink bug abundances have been lower than normal over the past two years, but have been an increasing problem over the long-term,” he adds.

Reisig pointed out increasing troubles in soybeans from the newly invasive pest Megacopta cribraria, commonly known as the kudzu bug. “This will likely be our most significant pest across all field crops,” he says.

Pay Heed to Insect Stages

Roy Boykin, an entomologist with Syngenta, suggests looking at prevailing weather trends, and keeping in mind an insect’s hibernation, pupae and larvae stages, and how weather affects each of them.

“The stage that an insect is in relates to the weather conditions,” Boykin says. “If you’ve got warm weather in winter, you can expect a larger population, but a lot of rain can nip that in the bud.
Likewise, if you have warm weather that leads to a hot, dry growing season, the extreme will limit insect populations. Extreme conditions tend to limit, while normal conditions tend to point at high insect populations.”

According to Purdue’s Bledsoe, a 5% variance from the previous year is a good way to forecast insecticide use. Purdue maintains a useful insect forecast website ( based on a 20-year history that details serious insect threats and when to expect them.

Seed Treatments Rise

The advent of transgenic produce and seed coatings has “changed the whole concept of the way we do things,” Bledsoe says. They allow growers to manage insects outside the realm of weather. These operate in crops systemically.

“Every single kernel has a seed treatment attached to it: a fungicide and a powerful insecticide,” Bledsoe says. “Back in the old days, we would just plant corn unprotected and would get bug damage. But now it’s a thing of the past.”

Bledsoe sees pest management waning, as the newer strategies reduce uncertainty. Transgenics and seed coatings offer systemic protection against insects at all phases of their development and regardless of weather patterns. For corn rootworm infestations, treatments alleviate 99% of the annual populations. Trade patents include Poncho from Bayer CropScience and Cruiser from Syngenta. Monsanto also offers FieldGuard and DuPont offers Herculex.

Of course, Mother Nature does fight back. Such is the case with Monsanto’s YieldGuard, Bledsoe says. Rootworms are building up resistances. In such cases, growers must use traditional insecticides to battle infestations.

According to Christian Krupke, director of the Purdue Extension, growers should take a risk management approach to treating crops. Ask the question, “Does the market value of the crop make it sensible?”
Transgenics and seed coatings can bump up the price of produce at the market. The use of Bt corn, for example, led to corn prices spiking from $2.75 per bushel to $7 per bushel. In the marketplace, that means a rise from $95 to $135 per unit (about 80,000 seeds) to $240 to $350 per unit.

Traditional insecticides still have a market alongside systemic treatments. In addition to insects developing immunities to systemic treatments, there is always a need to spray for secondary pests. “There are different categories of management,” Bledoe says. “So why not be thorough? Why not protect your investment?”

The advent of systemics has had an effect on the insecticide market, however. One such impact is the reduction of the need for certain types of applications. For example, with transgenic resistance to corn rootworm or cotton bollworms, different pest management is needed. A grower might need to apply less for cotton bollworm, but other pests (which were previously controlled with the same insecticides that were applied for corn rootworms) are suddenly more of a problem, and so a different insecticide program is needed.

Meanwhile, manufacturers are continuing to pump significant investment into new strategies as insects proliferate. BASF, for example, is introducing a bait technology to combat wire worms in Europe. Goldor Bait, which received provisional registration for potatoes in Germany, Australia and Italy, is an effective insect control with a high level of environmental and product safety, BASF says.

“The active ingredient of Goldor Bait, fipronil, is combined with an attractant,” Anne Burt, BASF group communications director says. “The worms get attracted by the seed and once they get in contact with the seed or eat it they become inactive. “Industry is always investing in new insecticide discovery pipelines that are geared for active ingredients and solutions for emerging insect problems,” she says.

Timothy Troy is a freelance journalist based in Cleveland, Ohio.