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6

IN THE SPACE

of five seasons, the

Western bean cutworm (WBC) has spread

to become a well-established threat across

Ontario. The question is, how?

Researchers from the University of Western

Ontario (UWO) are trying to understand more

about the pest’s overwintering habits and

basic biology so they can give farmers a

better idea of what conditions allow WBC

to reproduce, spread, and overwinter.

“I understand farmers’ frustration. They want

an answer right now and I don’t blame them,”

says Professor Jeremy McNeil, from UWO’s

Department of Biology. “But some of those

answers can’t be instantly generated, because

we don’t know much about Western bean

cutworm. With further information, we

may be able to improve on the current

management strategies.”

Currently, pheromone traps are used to

monitor for WBC moths in corn fields and

detect when the peak moth flight takes

place. Farmers then monitor their crops

for egg masses and spray once a certain

threshold is reached.

“We would like to relate the number of moths

caught to the number of egg masses or larvae

found in the field,” says McNeil. “And if you

could say ‘above this number of moths

caught per day, per week, in the trap means

we’re going to have more caterpillars and

intervention is needed.’”

However, there doesn’t always seem to be a

strong relationship between what’s caught in

the trap and subsequent WBC feeding damage.

One key aspect, says McNeil, lies in

understanding where many of these cutworms

are coming from. Are there bigWBC populations

overwintering in local fields, or are the pests

flying in from warmer geographies?

This is where knowing more about WBC

overwintering and biology could allow

researchers to develop a sort of early warning

system for major infestations.

“We know there are certain species of insects

that don’t overwinter here, but immigrate in

every year,” explains McNeil. “And in some

years, these insects can cause epidemics if

we get a very large population, and if the

conditions are ideal for them when they

get here.”

He compares getting a serious insect epidemic

to rolling three dice at a casino and getting

three sixes. The first six, McNeil says,

represents the conditions wherever the

insects are coming from, which need to be

ideal to have a big population.

The second six is the weather patterns that

will carry insect pests, like WBC, into Ontario

growing areas, while the third six represents

the weather and growing conditions when

the WBC arrives in Ontario.

“You might have had a freezing cold spring

where nothing’s been planted,” says McNeil.

“In that situation, even if hundreds of Western

bean cutworm moths arrived every minute,

they would all die.”

OVERWINTERING

But even if immigrant cutworm populations

were out of the picture, farmers may need to

be worried about local, overwintering WBC.

That’s why McNeil and his research team

are trying to learn more about the WBC’s

overwintering biology — namely how soil

depths, temperatures, and timing affect the

insects’ survival rates when they burrow

down into the soil as pre-pupae.

“We do know that there’s only one generation

of WBC a year, but they start early. The first

moths that lay eggs and the last ones that

lay eggs can be nearly a month apart,” he

explains. “So, you could have some going

into the soil in mid-August with others in

late September.”

This is important, as insects use day-length

and temperatures as a cue to overwinter.

But higher late-season temperatures in

September could be causing a much wider

overwintering period. McNeil is also working

with UWO biology professor Brent Sinclair

and graduate student Kurtis Turnbull to

understand how much energy the pest uses

while overwintering.

“One of the big questions for us is, do WBC

have enough energy to survive and emerge

as adults,” he says.

McNeil points out that the insects are also

cold blooded, so if the soil is cool with a snow

cover, the WBC pre-pupae use far less energy

while overwintering. But the warmer soil

temperatures are, the faster they use up

energy meant to last them through the

following spring.

McNeil and his fellow researchers suspect

that climate change and weather conditions

could play a big role in cutworm survivability.

This led them to set up a field trial at their

experimental farm outside of London, where

pre-pupal cutworm larvae were buried in cages

about one meter deep in the soil.

The idea, explains McNeil, is to infest corn

plots with the pest, then dig up some of the

cages in September, November, and March

to see how many insects have survived until

the spring. The researchers also look closely

at each cutworm’s fat content to see how

much energy the insects have used up

while underground.

So far, McNeil and his fellow researchers

found that 50 to 65 per cent of pre-

pupae cutworm larvae died by the end

of September — roughly one month after

burrowing underground.

“Of course, that doesn’t bode well for the

insect’s long-term survival until the following

June – especially when they need to survive

Western bean cutworm

OVERWINTERING BEHAVIOUR AND BIOLOGY

Joey Sabljic

continued on page 8

Cover story