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Cold Weather Effects On Insect Populations?
DR. SCOTT STEWART
JACKSON, TENN.
Hey, let’s face it. The reason we have more kinds of bugs in the South is because we have a warmer environment. However, not all insect pests are equally affected. Some are very tolerant of cold weather while others take a hit during a hard winter. Below are some examples.
1) Boll weevil: I know this one is eradicated in the Mid South, but this pest is one reason this question arises so much. Most people recall that boll weevils are sensitive to winter kill, and populations would be substantially reduced the year following a harsh winter.
2) Tarnished plant bug: Sorry, they can tolerate very cold winter, and this species actually occurs well into Canada. Don’t expect much in way of a winter kill, but a cold winter can definitely delay the weedy hosts that support early plant bug populations. How this affects populations that will occur in cotton is much less predictable.
3) Southern green stink bug: This species does not like the cold and rarely occurs in Tennessee except late season and/or after 2-3 consecutive mild winters. We will certainly see reduced populations across much of the South this year. I don’t expect to see one in Tennessee!
4) Green and brown stink bugs: They don’t mind the cold too bad and populations persist well north of Tennessee. They tend to have fewer problems with stink bugs in the Midwest because they have fewer generations and less time for populations to build to economic levels. I’m not expecting much winter impact in Tennessee.
5) Brown marmorated stink bug: An invasive pest from Asia, this species is well established in Pennsylvania, Virginia, Delaware and other surrounding states. It is also well established in the Knoxville and Nashville area. It is invading from the north and appears to do well in the cold. Indeed, hot summers may negatively affect the spread of this pest in the South.
6) Kudzu bug: Another Asian invasive that does not appear too sensitive to cold weather. We will find out more this year. However, both kudzu bug and brown marmorated stink bugs like to overwinter in homes and other structures, so we know some will make it through the winter. Based on its distribution in its native home range, this pest should make it just about anywhere kudzu is common in the South. However, the kick off to seeing the first generation will occur later as you move northward. I expect there is a place where only one generation (as opposed to two) occurs each year. This could be a help, but we don’t know where that line is yet.
7) Southwestern corn borer: The hard winter should give us some help here. Cold definitely hurts this critter. Thus, it rarely gets much further north than Kentucky and southern Illinois. I expect reduced problems in Tennessee during 2014.
8) European corn borer: This corn borer does just find in both northern and southern geographies. It has a history of being a major pest in the upper Corn Belt.
9) Threecornered alfalfa hopper: Tennessee is about this insect’s upper limit, and I’ve seen slow starts for this pest following previous cold winters. Expect the same for 2014, but populations may still rebound enough to be a problem in wheat beans.
10) Fall armyworm, beet armyworm, soybean looper, and velvetbean caterpillar: These pests typically do not make it through the winters in the U.S., except for extremely southern areas where it does not freeze. Our infestations originate from migratory moths in places like Puerto Rico, Mexico and South America. Thus, mid-southern temperatures do not predict much about the occurrence of these critters.
11) Green cloverworm, yellowstriped armyworm, corn earworm: These are native species with a broad distribution. I do not expected a predictable, negative effect from our hard winter. The corn earworm (i.e., bollworm) may have a little trouble making it through this last Tennessee winter, but it is a very cable migrator. How well it fares on spring hosts to our south probably will have a bigger effect.
12) Fire ants: Yeah, the winter should knock these guys back a good bit in Tennessee. Down but not out! Their distribution will likely continue to ebb and flow northward depending upon how harsh or mild the previous winters have been.
13) Twospotted spider mite: Nah, they will do fine despite the cold winter.
14) Japanese beetles: First found in the Northeast (New York, etc.) about 100 years ago. They have been moving our way ever since. Enough said!
We know less about the survival of the many important beneficial insects that help control insect pests. But bad effects on important beneficial insects favors a rapid build-up of pest populations. So there is some give and take here. Because most insect and mite pests have a high capability to reproduce, they can overcome initially low populations if conditions are favorable during the first generation after winter breaks. In my business, we call this job security!∆
DR. SCOTT STEWART: IPM Extension Specialist, University of Tennessee
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