Christian Krupke part of study suggesting
warmer temperatures could lead to boom in corn pests
By Elizabeth K. Gardner
Purdue News Service
December 16, 2008
WEST LAFAYETTE, Ind. - Climate
change could provide the warmer weather pests prefer, leading to
an increase in populations that feed on corn and other crops, according
to a new study.
Warmer growing season temperatures and milder winters could allow
some of these insects to expand their territory and produce an
extra generation of offspring each year, said Noah Diffenbaugh,
the Purdue University associate professor of earth and atmospheric
sciences who led the study.
"Our projections showed all of the species studied spreading
into agricultural areas where they currently are not endemic," said
Diffenbaugh, who is interim director of the Purdue Climate Change
Research Center. "The greatest potential range expansion was
seen with the corn earworm, which is known to infest other high-value
crops such as sweet corn and tomatoes. Warming could allow populations
to survive the winter in the upper Midwest, the key region for
corn production, as well as areas of the West where other high-value
crops are grown."
The United States is the largest corn producer in the world and
contributes almost half of the world's total production, according
to the U.S. Department of Agriculture. Within the United States,
corn and corn syrup are used in common food items such as cereal
and soft drinks, as well as being used as feed for livestock. Outside
of the United States, struggling countries depend on U.S. corn
crops to feed starving populations.
"The world depends on
U.S corn production for a variety of uses," Diffenbaugh said. "Ethanol
production and a growing world population are increasing demand
for corn. Expansion of the pests' ranges could have substantial
impacts through decreased yields and increased costs for seed and
Diffenbaugh collaborated with Purdue professors Christian Krupke,
an entomologist, and Corinne Alexander, an agricultural economist,
as well as with Michael White from Utah State University. The team
incorporated the survival temperature thresholds of each species
with a highly detailed climate change model for the United States.
A paper detailing their work was recently published online in Environmental
"Basically, we examined both the number of days warm enough
for the pests to grow and the number of days cold enough to kill
the pests, assuming the pests' documented climate tolerances remain
the same," Krupke said. "This tells us what could happen
in projected future climates. However, the model cannot take into
account the dynamic nature of any ecological system. There are
significant additional factors that could come into play such as
interaction of the pests with the environment, relocation of corn
and other crops and changing human management of the pests."
The research team studied the potential end-of-the-century distributions
of the corn earworm, Heliothis zea; the European corn borer, Ostrinia
nubilalis; northern corn rootworm, Diabrotica barberi; and western
corn rootworm, Diabrotica virgifera virgifera.
The team used the
physiological thresholds for each species coupled with models of
development to determine how each would respond to projected climate
For example, the pupal stage of the corn earworm
overwinters and cannot withstand more than five days at temperatures
below 14 degrees Fahrenheit. It also requires six days at a temperature
of about 55 degrees Fahrenheit to complete development. By including
these parameters in the climate model, the team was able to project
future temperature-based distributions for each pest, Diffenbaugh
Krupke said the insects in this study should not be adversely
affected by temperature increases.
"The limiting factor for these pests is usually cold tolerance,
specifically their ability to overwinter and re-infest the crop
the next season," he said. "Increases in temperatures,
even summer temperatures, generally benefit these pests. An effectively
longer season, or more days exceeding their minimum temperature
range, provides them with additional time to feed, mate and reproduce."
corn earworm is of particular concern because it is migratory and
pesticide resistant, he said.
"The corn earworm is an established
global pest, and particularly in the Southern U.S., where it has
proven difficult to manage," Krupke said. "It is resistant
to several existing pesticides, and adult moths are capable of
being transported long distances in the jet stream to infest new
Alexander said a reduction in corn yields could have
substantial economic and social impacts, including higher food
prices and reduced food supply.
"Losses due to insect pests, including the resources required
to control them, is the biggest cost for corn production," Alexander
said. "The European corn borer has been estimated to cost
the United States around $1 billion annually, and the corn earworm
is responsible for destroying about 2 percent of the corn crop."
corn reserves add to the impact of a poor growing season. The 2007-08
30-year low inventory resulted in the United Nation's Food and
Agricultural Organization Food Price Index increasing by 47 percent,
with cereal prices increasing 62 percent, she said.
increasing demand and a limited supply, even small reductions in
yield, for example from a pest expanding its range by 60 miles,
could result in substantial economic and social consequences," Alexander
said. "In addition to loss of yields, the variation in yields
could drive up the costs of insurance and disaster relief for farmers."
research team next will look at a broader range of crops and will
work to create a more complete modeling framework, Diffenbaugh
The team used a high-resolution climate model, believed to
have the greatest detail currently available for the United States,
to project daily temperatures for specific regions.
For the study's
climate change scenario, the research group used a commonly accepted
A2 emissions scenario from the Intergovernmental Panel on Climate
Change that assumes greenhouse gas emissions continue to increase
The Purdue Climate Change Research Center is affiliated
with Purdue's Discovery Park. The center promotes and organizes
research and education on global climate change and studies its
impact on agriculture, natural ecosystems and society. It was established
in 2004 to support Purdue in research and education on regional
scale climate change, its impacts and mitigation, and adaptation
strategies. The center serves as a hub for a range of activities
beyond scientific research, including teaching, public education
and the development of public policy recommendations.
were carried out using computational facilities in Purdue's Rosen
Center for Advanced Computing, which is supported and administered
by Information Technology at Purdue.
The National Science Foundation
and National Aeronautics and Space Administration partially funded