DECATUR, Ill. (DTN) -- It's hard not to be attracted to a blooming sunflower field this time of year. The bright smiling yellow faces appear like rays of sunshine against the backdrop of browning corn and soybeans.
I expected to find honeybees hunting for pollen in this late blooming field of sunflowers that were double-cropped following wheat. There's not a lot for bees and other pollinating insects to forage on this time of year. What I didn't expect to find were large amounts of adult corn rootworm beetles -- both westerns (with the striped backs) and southern (polka dotted) joining in the feeding frenzy.
Their presence was a reminder of how critical it is to evaluate rootworm controls this fall. It was a relatively quiet summer for rootworm feeding reports. However, we found a surprising number of adult rootworm beetles and some lodged corn while pulling yield samples during the Pro Farmer Midwest Crop Tour in August -- particularly as we sampled in western Illinois and eastern Iowa.
Earlier this month, University of Illinois entomologists announced they had found significant western corn rootworm larval injury in some first-year cornfields that had been planted to Bt rootworm hybrids expressing the Cry3Bb1 protein. That discovery is important because it now means some populations of rootworms have been able to overcome two management practices -- rotation and Bt traits -- in the same field.
Testing to see if rootworms are "resistant" is no easy task. University of Illinois entomologist Joseph Spencer spends much of his time rearing rootworm babies and trying to determine if the suspected Bt-resistant populations are indeed resistant.
This involves a complicated procedure of inoculating both Bt-hybrids and near isoline non-Bt hybrids with rootworm larvae. However, before this happens, he must get females from each suspected Bt-resistant population to lay enough eggs to do the tests. "The trick is to get eggs to hatch at around the same time as corn plants are ready to accept them," Spencer told DTN.
"You also need similar numbers of insects from Bt-susceptible populations to run alongside the suspect populations as controls. Fortunately, eggs from these populations are available from the USDA lab in Brookings, S.D.," he said. "They were collected from the field before Bt-corn was ever commercialized and they are a terrific resource."
Spencer said while the susceptible populations were not collected with the intention of this use, the fact that USDA scientists and others collected these insects and have maintained them turns out to be a very important. "Without these susceptible field insects, it would be a lot harder to assess resistance and we would have a much poorer understanding of how pest management has affected this important pest," Spencer said.
As it turns out, there is a high bar to clear before resistance can be formally determined. "There is an on-going conversation about what tests should be used to confirm resistance -- scientists, regulators and the biotechnology companies are all involved and I think there is cooperation that is leading somewhere," he said.
"In the meantime, mounting growers' field accounts, university research and industry responses to poor performance indicate that there is little doubt that resistance to some Bt traits is present in the Corn Belt," Spencer added.
For farmers, that intensifies the need to pay more attention to fields this fall and what they have or have not done to manage corn pests. Those observations are critical to the selection of traits and evaluating the need for planting-time soil insecticide for 2014.
Spencer said it is likely many soybean acres quietly hosted vigorous populations of Bt and crop rotation resistant egg-laying females this summer. "With no attention paid to monitoring abundance in those fields, more surprises could be in store for some of the 2014 rotated corn," Spencer said. "I also expect that as combines begin to roll and growers encounter patches of downed corn, there will be more awareness of the new problem with rotated Bt-corn."
Pamela Smith can be reached at Pamela.email@example.com
© Copyright 2013 DTN/The Progressive Farmer. All rights reserved.