6 - Corn Earworm Susceptibility to Bt Corn Proteins
Dr. Robert Wright, Professor of Entomology and Extension Specialist - Corn earworms don’t overwinter in Nebraska, but moths fly north from the southern U. S. each spring. In the south they develop on Bt cotton and Bt corn. Resistance to Bt traits has been detected in the southern U.S. This study is part of a multistate project to determine the distribution of Bt resistance traits in the U. S. It has implications particularly to seed corn and food grade corn production in Nebraska.
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[00:00:04.350]Okay, this is Bob Wright.
I'm an entomologist.
[00:00:07.110]I do a lot of my field research out
here at the South Central Ag Lab.
[00:00:11.250]And we like to talk about a new study.
We started this year on corn earworm worms.
[00:00:15.600]Corn earworm are not
a major pest of field corn,
[00:00:19.170]but there are types of corn in
Nebraska that we have such as popcorn,
[00:00:24.000]seed corn and food grade corn,
[00:00:26.760]where they can be economically
important pests. Corn earworm
[00:00:30.180]this study started out with sweet
corn entomologists in the, corn earworm
[00:00:35.040]mid Atlantic States and upper Midwest
where they grow a lot of sweet corn.
[00:00:39.180]And we're testing whether the,
[00:00:40.920]the corn earworm in this area
have tolerance to different BT
[00:00:45.450]traits. And so what we have
here is, is BT sweet corn.
[00:00:50.010]We have two different types of
actually three different BT proteins
[00:00:54.450]expressed in these different
hybrids and also some non BT
[00:01:00.750]And so the corn earworm does
not overwinter in Nebraska.
[00:01:05.130]It overwinters in the Southern half
of the U S. And so the, the, corn earworm
[00:01:10.320]corn earworm worms had come up here,
have developed on crops in the South,
[00:01:15.360]and we have BT cotton
and BT corn in the South.
[00:01:19.290]And we think what has happened.
[00:01:21.060]We're started to see resistance
to BT in some of the Southern
[00:01:26.940]And we're started to see that show up
in the Northern populations that migrate
[00:01:30.750]from the South. So, corn earworm we've,
[00:01:34.350]we've seen in the past that PI rethread
resistance that developed in the South
[00:01:38.550]has moved up to the Midwest
as well. The same way. Corn earworm
[00:01:43.380]the corn earworm feeds
in the ear tip, corn earworm
[00:01:47.040]is attracted to late the mods attracted
to lay eggs on green silk stages,
[00:01:51.870]which is what we have right
here. And we hope to get, corn earworm
[00:01:55.440]some egg laying in the
next couple of weeks.
[00:01:57.360]We'll evaluate this when it's the time
that we would normally harvest sweet corn
[00:02:02.850]and see if we have survival
on the different BT traits.
[00:02:07.710]This is part of a multi-state
project, corn earworm from the East coast, corn earworm
[00:02:12.120]to Nebraska, multiple States are
generating data on this study.
[00:02:17.040]And so we'll have more information
in the future about the status of,
[00:02:21.750]corn root worms in Nebraska,
whether they have resistance to BT.
[00:02:26.580]The last couple of years,
we've gotten more reports.
[00:02:28.950]People saw poor performance, corn earworm
[00:02:32.070]or they saw more corn earworm where
they thought they wouldn't in either BT
[00:02:36.480]corns or, corn earworm
[00:02:38.310]other other crops or sweet
corn and BT sweet corn.
[00:02:43.230]So we've had some indication that we
might have some changing resistance in
[00:02:47.400]Nebraska to corn earworms,
[00:02:50.250]corn earworm overwinters in
the pupal stage in the soil,
[00:02:54.120]in the Southern us emerges early, corn earworm
[00:02:57.400]starts laying eggs on a variety
of crops. It has a multiple, corn earworm
[00:03:01.750]different common names. It can be
called the cotton bowl, worm tomato,
[00:03:05.260]fruit worm, soybean pod worm,
[00:03:07.840]as well as the corn earworm to reflect
the number of crops it can grow.
[00:03:13.390]And so, corn earworm
[00:03:15.160]one thing we can do in this
study is test to see whether
[00:03:20.050]we have BT proteins in the
different, corn earworm varieties.
[00:03:24.610]And there are some quick
strips tests that we can do.
[00:03:34.610]Type of a protein has
a different strip test.
[00:03:39.720]And so this shows that one of the,
[00:03:41.550]one of the BT corns is expressing
the BT protein that is supposed
[00:03:46.320]to. And so if we see
resistance or survival,
[00:03:50.010]we know it's due to resistance.
[00:03:52.140]We also have a test strip from the
non BT corn with no lines on the
[00:03:56.850]test rep showing that no
BT is being expressed here.
[00:04:01.200]So that's sort of a quality control we
can do to make sure that what we see is
[00:04:06.180]actually due to resistance.
[00:04:08.160]The alternative to this type of study
would be to collect a lot of moths and
[00:04:12.260]Rear them out in the lab and test larvae
individually against different BT
[00:04:18.060]And that's relatively labor
expensive to do this
[00:04:22.470]approach is to put out different
hybrids with different traits,
[00:04:26.460]and basically let the, corn earworm the insect
do the work, corn earworm to find the sweet corn.
[00:04:31.320]Then we'll come back in a couple of
weeks and see if anything is surviving in
[00:04:35.520]these different hybrids and
what that means about survival.
[00:04:40.350]Typically in field corn, it's
not a concern for corn earworm worms,
[00:04:45.510]corn earworm because they typically
feed just in the ear tip.
[00:04:48.360]This is field corn here at the station.
[00:04:53.520]And so we have some,
[00:04:55.650]here's a corn earworm where I'm feeding in
the ear tip right now it's about half
[00:04:59.520]grown. Corn earworm
[00:05:01.170]typically we only find one mature
larva in an ear because they're
[00:05:05.760]cannibalistic. And if we have more than
one they'll feed on each other, corn earworm
[00:05:10.290]and typically they'll just feed in the
ear tip a lot of times they're just
[00:05:13.410]feeding on these undeveloped ears
and research has shown that in
[00:05:18.300]field corn, it doesn't pay
to treat for corn earworms.
[00:05:21.750]It may pay to treat in other, other
corns. Like we talked about popcorn,
[00:05:26.040]seed corn or sweet corn or food grade.
[00:05:36.330]So we'll be reporting this data later
in the year as we get information.
[00:05:40.620]And also what we're seeing
in other States, corn earworm
[00:05:43.380]they have seen resistance to BT
some of the BT proteins in the
[00:05:47.880]South. And, corn earworm
[00:05:49.980]so we're wanting to see if we can also
find it in the Midwest and that'll help
[00:05:53.940]us, corn earworm make our management
accurate for this area.
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