Cold may have thinned insect pests

As we finally see spring conditions, farmers and others are asking whether insect pests will be reduced because of the severe winter.
Normally, Ohio seldom gets cold enough to help cause significant mortality during the winter. However, the later severe cold spells may have reduced some insect pests that spend the winter in Ohio.
Cold temperatures have reduced insects in the past. A good example of this occurred in 1983, when a late cold spell cut the Mexican bean beetle, killing off a statewide problem that was beginning in soybeans.
Some insects will not be affected at all since they do not spend the winter in Ohio and migrate from warmer climates during the growing season. These include true armyworms and black cutworms in early summer, and potato leafhoppers later in the summer.
Also, some insects such as the soybean aphid and western corn rootworm were already expected to be low this year.
Soybean aphid populations tend to follow a two-year cycle of low and heavy infestations. This year is already expected to be bad for soybean aphids.
Western corn rootworm numbers have been low for the past few years, including last year. There is no reason to expect anything different this summer.
Thus, if numbers of rootworms are again low, will it be from having had low numbers already, or was it the cold spell?
The main pests that may have been affected are bean leaf beetles and Mexican bean beetles on soybeans; Japanese beetles and slugs on soybeans and corn; and the relatively new western bean cutworms and Asiatic garden beetles on corn.
All of these spend the winter in Ohio, and perhaps the cold spell will reduce the initial population.
One pest that should be affected is the corn flea beetle. They generally cause minor feeding damage, but a more serious problem is Stewart’s bacterial wilt and leaf blight, which may be transmitted by feeding flea beetles to both field and sweet corn.
Entomologists use a flea beetle index to project estimated flea beetle populations by adding the monthly average temperatures for December, January and February.
If the sum is greater than 90, corn flea beetle populations will be expected to be at levels to cause concerns from Stewart’s bacterial wilt.
However, all observation sites in Ohio had values below 90 this past winter, and the northwestern Ohio site had the lowest score for the state.
We know less about the survival from severe cold of many important beneficial insects that help control the pests. Adverse effects on important beneficial insects may favor a rapid buildup of pest populations.
Because most insect and mite pests have a high capability to reproduce, they can overcome initially low populations and rebound quickly once temperatures warm up.
Thus, at this time it is speculation on what might happen until we actually see lower numbers during the growing season.
Insects are quite adaptable. They tend to spend the winter in protected places, and the heavy snow cover was also a good insulator for them. However, this past winter would have tested their survival.
Lentz is extension educator for agriculture and natural resources for The Ohio State University Extension Service in Hancock County. He can be reached at 419-422-3851 or via email at
Lentz can be heard with Vaun Wickerham on weekdays at 6:35 a.m. on WFIN, at 5:43 a.m. on WKXA-FM, and at 5:28 a.m. at 106.3 The Fox.


About the Author