Cold Temperatures and the Potential for Insect Mortality on Soybean

By Ron Hammond and Andy Michel, Department of Entomology, Ohio Agricultural Research and Development Center, The Ohio State University

This past winter had two instances of extremely cold temperatures, well below those that are considered normal low temperatures in Ohio.  After any cold winter, we get questions as to whether insect mortality might have occurred, and our answer has been that it is usually not cold enough to be a factor in causing significant insect mortality during the winter months.  However, the extreme cold this past winter has the potential to change that thought, at least for those pests that overwinter in Ohio.  An example of what can happen occurred in the winter of 1983-1984 during an extreme cold spell that caused significant mortality to Mexican bean beetles which had been causing considerable grower concern across Ohio.  Since that winter, this insect has never threatened soybean growers except in a few counties in east-central Ohio.

Will growers see similar mortality to the various insects that are a threat to soybeans?

At this time, we can only say it is a possibility; however, we will not be able to tell what happens until we actually see insect numbers, or the lack of them, during the growing season.  The insects that overwinter in our state have a tremendous ability to survive severe conditions, although we are pushing the limit this winter.   Insects overwinter in protected places, and growers also need to consider heavier snow cover which is a good insulator.

Which soybean insects fit into this category of overwintering in Ohio that might be affected?

On soybeans, insects or other pests of interest include bean leaf beetles, Japanese beetles, Mexican bean beetles (at least in localized areas), stink bugs, slugs, and the soybean aphid.  However, soybean aphids should be considered slightly differently.  The main thought is that the aphid has always occurred in a two-year cycle; a high soybean aphid year is followed by a very low year, where aphids are difficult to find in the state, let alone at a level causing concern.  Because the past summer of 2013 was a high year, with aphids common on soybeans and at economic levels in many fields, we expect this coming summer to be a low year.  We already expect soybean aphids to be at very low to non-existent levels.  Thus, if aphids are indeed lower, will it be because of the two-year cycle, or significant mortality caused by the cold winter?  It will be more interesting to see what happens in 2015, a year that should be a high aphid year.   If the cold spell we experienced this winter has a negative impact on their populations, perhaps it will be more noticeable the following year.

A specific stink bug should be mentioned, and that is the newest pest of grower concern, the brown marmorated stink bug.   It will be interesting to see what happens to this insect following this extreme winter for no other reason than this has been the first “really cold winter” that it has experienced since its introduction into the U.S.   Will the insect be able to handle those extremely low temperatures?  Or will they suffer significant mortality?  We will need to keep close watch this summer to find out the answer.

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