Production Blog
Emily Unglesbee DTN Staff Reporter

Monday 08/25/14

The Trouble With Time

CHAMPAIGN, Ill. (DTN) -- University of Illinois entomologist Joe Spencer likes to boast that he has the highest concentration of western corn rootworms in the state in his university lab.

Don't wait for the official word on Bt-resistance to dig roots and react to significant root pruning on Bt-hybrids, shown on the right. (DTN photo by Emily Unglesbee)

He's probably right. Great hordes of the tiny black and yellow beetles swarm and flutter inside more than a dozen aluminum cages in his lab, where Spencer encourages the beetles to produce enormous numbers of egg by fattening them on sweet corn.

These insects were swooped into Spencer's net in fields in northern Illinois this summer, where farmers found significant root damage on first-year Bt-corn hybrids in the summer of 2013. Farmers in Kankakee and Livingston counties first alerted Spencer and another University of Illinois entomologist, Mike Gray, to the possibility of rootworms with dual rotation -- and Bt-resistance last August. The entomologists immediately collected insects and spirited them back to the lab that same month.

Now, almost a year later, Spencer says he is still at least a month away from having concrete answers to share with the growers or the scientific world.

Why? Time is a troubling obstacle for rootworm researchers. Confirming resistance in rootworms requires hatching the eggs of the females with suspected resistance, allowing their larvae to feed on Bt-roots, and monitoring them to see if they survive. Unfortunately, this bioassay process can take almost a year to complete, so growers cannot wait for official confirmation before they react to rootworm damage on Bt-corn hybrids.

To start the confirmation process, researchers have to first round up large quantities of the beetles in question and encourage them to mate and lay eggs.

Never grab your lunch blindly from the two refrigerators in Spencer's lab. When he isn't stuffing the rootworm beetles with food, Spencer is on to the second step: packing away hundreds of thousands of their eggs into the fridges.

Rootworm beetle eggs need nearly five months of cold exposure before they will hatch, which is the largest factor contributing to the time lag between the discovery of root damage and the confirmation of resistance.

For example, the beetles currently munching on sweet corn in Spencer's lab were caught this summer. Yet the eggs that he is pulling from cold storage to hatch are from the samples collected in August of 2013.

About three weeks after they leave the fridge, Spencer and his assistants will transfer groups of 10 larvae onto the roots of Bt-traited or non-Bt corn. After 17 days of feeding, the researchers collect the larvae, measure their sizes and tally up how many survived on each type of corn.

If the beetles from August 2013 are Bt-resistant, similar numbers will survive on both the non-Bt and Bt-roots, Spencer explained.

In the fields where those suspected Bt-resistant beetles were caught last year, farmers had diligently rotated corn and soybeans for 20 years, and yet they are struggling to manage unexpected damage to their Bt-corn hybrids. They want answers.

The growers will be among the first to know the results of the resistance tests in the next month or two, Spencer said. Yet already, these farmers have had to purchase corn hybrids for 2014, and soon they will need to make seed decisions for 2015, all without concrete information about resistance in their fields, he pointed out.

"It's a very long process. We need something faster," he said. "It's very hard for farmers to take an IPM [Integrated Pest Management] approach when they have incomplete information about the nature of their problem."

Until a faster method comes along, all farmers can do is dig and react quickly. If the roots of your Bt-corn hybrids show significant pruning, don't wait a year until scientists can confirm resistance before you change tactics.

Although official Bt-resistance confirmation takes time, entomologists work quickly each summer to write up results from their rootworm trials so farmers can make more informed seed decisions, University of Illinois entomologist Mike Gray noted.

Already this year, Gray has published the preliminary results from the University of Illinois 2014 rootworm test plots. In their plots across the state, Bt-hybrids expressing only Cry3Bb1 or mCry3A continued to show very poor protection against the western corn rootworm. Researchers also found that adding a soil insecticide to Bt-hybrids in the one trial did not produce significantly more protection than using the soil insecticide alone.

These results and past research all suggest that farmers have the following options to draw from if they find unexpected damage to Bt-corn roots: Rotating to soybeans, switching to a hybrid expressing a different Bt-protein, moving to a pyramided Bt-hybrid, or using a non-Bt hybrid with planting time soil insecticides.

"Please don't wait until a problem exists on your farm before you start to actively manage [rootworms]," Pioneer research entomologist Murt McLeod told growers at the company's Research Station Open House near Champaign, Ill., last week. "When you officially have resistance, that battle is going to be much more significant and much more difficult."

Emily Unglesbee can be reached at

Follow Emily Unglesbee on Twitter @Emily_Unglesbee


Posted at 11:07AM CDT 08/25/14 by Emily Unglesbee
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