EAST LANSING, Mich. — Western bean cutworm (WBC) continues to threaten corn and dry beans throughout the Great Lakes region and parts of Canada, but researchers this year are seeing evidence the threat is declining.

According to Michigan State University field crops entomologist Chris DiFonzo, based on this year’s research as compared with data collected since 2008, “2012 had the lowest average catch by several times. The peak looked to be July 14, which is the earliest on average.”

DiFonzo leads a research project funded by MSU’s Project GREEEN (Generating Research and Extension to meet Economic and Environmental Needs) and the state’s corn and dry bean industries. She and her team monitor moth flight timing, egg deposits and larval feeding of the pest throughout the state.

They also cooperate with a group of entomologists around the Great Lakes region, including Canada, which helps them better understand WBC and determine management recommendations for growers. She said the moth flight was lower this season – a trend she first noted in the last growing season.

“Because flight was more spread out, egg laying was likely ‘diluted’ among more fields in the landscape. We may end up with some WBC damage to corn and dry beans, but distributed differently, across more fields,” she said.

In the fields this year, she said fewer live larvae are hatching from egg masses than during past years. These larvae can cause severe feeding injury to corn ears and to pods of dry beans, resulting in loss of yield and quality. “In previous years, with a tighter emergence and bigger peak, we saw an all-or-nothing pattern of infestation in corn, based on crop stage. Some fields had no larvae because they were at the wrong stage to attract females, while pre-tassel fields were over threshold because they were highly attractive for egg laying,” DiFonzo said.

“This year, we could find egg masses at many locations, but at very low levels compared to the past. If so, this would be good news for corn, since fewer fields will be over threshold.”

Above-average temperatures in July may have reduced egg laying by stressing or killing female moths. As more Bt (pest-resistant) corn containing the Cry1F trait is planted, there are fewer cornfields in the landscape that can produce large numbers of larvae. The natural control and Bt hybrids may be reducing the population over the landscape.

“Another big difference in 2012 is a big increase in biological control,” DiFonzo said. “Last year we observed occasional predation and limited parasitism in the field. But this season, many of the egg masses we find are partially eaten; many have a predator consuming the egg mass even as we collect it. When we hatched egg masses in individual containers, we found that parasitism rates were way up. The bottom line is that egg masses were getting hit hard by natural enemies this year, and hatching success was much lower.”

A spray advisory to safeguard against WBC in dry edible beans was issued on Aug. 1 for several counties in central and northern Michigan, because of high trap counts and the known potential risk of the pest to the dry bean crop.

WBC has been present in Michigan for several years. During the 2007 growing season, the northwestern quadrant of the state, from Oceana County to Montcalm County and north, was infested. In 2008, there was significant damage to dry bean crop in a few locations. Most beans in Montcalm County were sprayed in 2009 and 2010, but those left untreated had significant damage.