Fannin, Saturday, Octafcar It, Ht 2
Scientists battle European corn borer
By Joan Easley
NEWARK, Del. - Agricultural
scientists go to great lengths to
slow down a destructive insect like
the European corn borer. In the
1940 s they went to Europe in
search of natural controls.
There they found several insects
that parasitize die com borer.
They brought these insects back to
the United States to see if they
would establish themselves and
keep U.S. com borer numbers
down.
The one that seemed most
promising was a hungry little fly
called Lydella. For the next
several years it did a creditable
job of controlling com borer
populations in Delaware and other
corn-growing states in which it had
been introduced.
During the 19605, however, Paul
Burbutis, University of Delaware
Agricultural Experiment Station
researcher who was heavily in
volved in the Lydella project,
discovered that for unknown
reasons the parasite had disap
peared in this country.
Burbutis decided to try again. He
and two researchers from the
nearby U.S. Department of
Agriculture Beneficial Insects
Laboratory, Larry Ertle and
Richard Dysart, imported
thousands of European com borer
larvae from Yugoslavia. They
knew that about 10 percent of the
borer larvae in that country carry
the Lydella parasite.
To find out which, though, they
had to raise all the larvae to
maturity and wait for the parasites
to emerge. In the interest of safety,
they carried out this work in the
quarantine facility of the USDA
lab.
They released Lydella in
Delaware and New Jersey in 1974,
1975, and 1976. However, winter
checks of the fields during 1975 and
1977 failed to turn up any surviving
Lydella. The researchers decided
their attempt to reintroduce it had
been a failure.
During a routine com borer
survey in 1978, however, a few
Lydella parasites turned up.
Encouraged, the researchers
employed a student, Nate Erwin,
to conduct a systematic search
throughout the state. He found a
few more surviving pockets of
Lydella.
Since 1979, Lydella has continued
to multiply and spread throughout
Delaware. Other corn-growing
regions, encouraged by
Delaware’s success, would like to
reintroduced the parasite too.
University of Delaware
Agricultural Experiment Station
researcher Charles Mason has
agreed to try to reintroduce
Lydella to lowa, Missouri,
Nebraska, and possibly Minnesota.
He’s working with mid-western
entomologists to learn why Lydella
disappeared in the first place so it
won’t happen again.
Past experience and a search of
the literature have given Mason a
few hints that may help insure the
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success of the midwestem reih
troduction attempt. The evidence
seems to indicate that Lydella is
better able to survive near large
bodies of water. This is probably
because Lydella also parasitizes
the stalk borer, an insect that feeds
on grasses common to wetter
areas. For that reason Mason will
release the parasites near water.
Whether he succeeds or fails in
his initial attempt to re-establish
the parasite in the Midwest, Mason
will pay close attention to what
happens in hopes it will help him
understand the factors that led to
the parasite’s first disappearance.
If the parasite fails to reestablish
itself, he hopes to find out why. And
if it succeeds, he will want to know
what factors influenced population
numbers.
Agricultural conditions vary
from year to year. Farmers switch
varieties and chemicals, and the
weather changes. Any of these
factors could have caused
Lydella's disappearance.
Mason is considering the
possibility that a change in com
varieties caused the problem.
Lydella deposit their young as
living larvae at the base of- the
entrance hole to the com stalk
created by the com borer. But they
refuse to do this on some com
varieties, perhaps because these
lack certain chemical attractants
that other varieties possess.
Midwestern scientists are pur
suing this line of research. '
There are other possible ex-
planations for the parasite’s
disappearance. Perhaps en
vironmental conditions became
less favorable to Lydella and more
favorable to one of its ecological
competitors such as a disease
organism or another parasite of
the European com borer. Even
more complicated, nature has
created a miniscule wasp that
parasitizes the Lydella fly. A
change in environment could have
allowed the wasp to thrive at
Lydella’s expense.
To test whether a chemical may
have caused Lydella’s disap
pearance, University of Delaware
graduate student Bob Leighty is
feeding sublethal doses of in
secticide to com borers in the
laboratory. Some of the borers
. in the experiment are parasitized
by Lydella. Leighty wants to learn
whether a dose of insecticide that
is only slightly harmful to the
borer could be fatal to the parasite.
If so, entomologists will have to
reconsider pest control recom
mendations so as to maximize
Lvdella’s chance of survival.
Wherever possible scientists
prefer to rely on nature’s own pest
control mechanisms such as Lydell
instead of chemicals. Now through
the efforts of University of
Delaware and USDA en
tomologists, Lydella is back on the
job in Delaware. With a little luck
it will soon be back at work in the
rest of the United States, and
scientists will know what to do to
keep it there.
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University of Delaware Agricultural Experiment Statioi
researcher Charles Mason checks for corn borer damage ii
hopes to re-introduce the corn borer parasite Lydella tothi
Corn Belt.
10 AM to 3 PM
Mi
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PLAN NOW TO ATTEND
Tuesday, November 2
Wednesday, November 3
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