Mild winter’s impact on insect populations

GENESEO, Ill. — Monthly average temperatures during “meteorological winter” were above freezing throughout a sizable chunk of Illinois, and the $64,000 question is — how has that impacted insect populations?

Kelly Estes, an entomologist with the Illinois Natural History Survey at the University of Illinois and the state’s agricultural pest survey coordinator, was a guest on Wyffels Hybrids’ “Keeping It Independent” podcast with Ryan Gentle, Wyffels Illinois agronomy manager, to address the buggy outlook and statewide trapping program.

Q: Trent Ford, state climatologist, said it was the warmest February ever in Peoria this year and in a few other parts of the state. There was a cold snap, but there was a lot of snow at the same time. What impact, if any, do these factors have on insects and their survivability?

A: Insects are temperature dependent, and they are going to overwinter in lots of different life stages. Some are overwinter as eggs like rootworms. Japanese beetles are overwintering in the soil as late instars, and as it warms up, they’re going to pupae and emerge as adults.

Stinkbugs overwinter as adults in what they consider protected areas. Brown marmorated stink bugs is an invasive that we’ve been dealing with for a couple of years and they’re overwintering in homes and barns. Temperature plays a part with them, but also day-length is increasing, so they’re activity is increasing, as well.

As the temperature drops, insects super cool their body to the temperature around them. So, when you start talking temperature swings, it gets warm and then they start to warm up and if you have a cold drop sometime they can’t adjust their body temperature.

When you have wild temperature swings, it can impact population. Severe cold can impact populations. Snow cover is insulating, so is it as cold where they are compared to what the ambient temperature is.

In looking at temperatures in December, January and February — meteorological winter — and at average temperatures based on that, we can predict Stewart’s wilt, which is not a huge deal overall for commercial growers because of resistance, but for sweet corn growers and maybe even seed corn companies, that plays a little bit of a different part.

Those average winter temperatures have been like 34 degrees, 35, 38 throughout most of the state. Overall, we’ve had a warmer winter, which indicates we will probably have greater insect survival.

Q: Another frequently asked question for agronomists in early spring is their views on rootworm hatch and survival. Warm weather is already producing growing degree units. Will this possibly move the rootworm to hatch early?

A: In mid-July every year we have our statewide survey we’re looking at insect populations throughout the state. We look at rootworm beetles in two ways — counts on corn and also sweeps in soybeans — hoping to get a general indication of corn rootworm populations.

It’s a little hard because it is just a random sampling throughout the state. We don’t know what management strategies are being employed by different growers and what’s going on exactly in the fields. But, overall, our averages of corn rootworm beetle populations have been pretty low.

Q: Are there areas in the state that we’re seeing higher populations?

A: Yes, there are. While our survey will give a good indication of an average and maybe trends, things are happening locally at different levels and we’re seeing that as we survey, even throughout the county. We sample here and there’s nothing and it’s a different situation five miles down the road.

Even though populations on average are low, survivability of eggs from the warm winter is probably pretty high.

The wild card that we have going into the spring, it’s warming up earlier, so things could move a little faster. Insects are temperature dependent. If it warms faster and higher temperatures, development comes earlier, development comes faster.

We’ve seen this several different years where we have a really wet spring, particularly when eggs are hatching. The saturated soils will definitely play a part in larval survival.

Do we have potential for rootworm populations that will be there? Yes, we have to get through the spring and hatch to find out what we might actually end up with.

Q: A statewide network of cooperators monitor insects through trapping, field monitoring and sample collecting. The work provides timely information on pest populations with insect trapping in the spring and summer surveys.

A: The spring trapping season is actually one of my favorites. Some insects overwinter in Illinois in different life stages. We have several predominant agricultural pests that migrate from the south.

They overwinter in the south and then head north when it starts to warm up, when you have storm fronts, rain and wind coming in from the south — those are great opportunities to bring pests into the state. Two of the primary ones we focus on in the spring are black cutworm and true armyworm.

This program has been around forever. When I started at the university, my predecessors were entomologists Rick Weinzierl in specialty crops and Mike Gray and Kevin Steffey in field crops.

They had been part of this program for many years and a lot of it was run through the Extension office because every county had their own Extension office and their own agent.

But times have changed and we have a lot of interested growers that like to do this stuff, too. So, we utilize Extension.

We also utilize grower volunteers or industry volunteers. I even had a bridge club that tried it out last year. We’re open to whoever is interested in learning more what’s going on not only in their field, but in their area.

Q: How many cooperators do you have across the state for the insect monitoring program and are there areas where you could use a few more?

A: We like to get volunteers from every area of the state. We get a lot through central Illinois and then I start working with some of my contacts in northwestern Illinois.

Southern Illinois has been one of the harder places to get some volunteers in the last couple of years, but that’s when networking comes in great because I can start asking — do you know somebody or can you persuade somebody into doing this for me? If anybody is ever willing, we want them to have that opportunity.

This is a program that’s funded through a USDA National Institute of Food and Agriculture grant. It not only funds spring trapping, some seasonal summer trapping with different pests, and also our statewide survey that we do in the summer, as well.

It’s been very supportive of what we want to do to get a good indication of what’s happening with insect pests in Illinois.

Q: Does monitoring through insect surveys in southern Illinois provide a heads-up with the migrating pests moving up from the southern states?

A: It is important. For these pests that are moving south to north, we definitely want to get traps in southern Illinois first.

I think one of the most interesting things that we’ve learned over the years with this trapping program is we may not see anything in traps in southern Illinois and you may pick up something quicker over in, for example, Fulton County.

These moths are caught in these weather fronts and winds that are coming through and as they move they are falling out randomly. So, there could be an area where you see a lot of insects in a trap, and five miles down the road you don’t.

Coverage regionally is good because it gives us an indication of what’s going on in an area. So, even if you’re catching insects in your trap and your neighbor who is also trapping isn’t that doesn’t necessarily mean that they shouldn’t be aware of what’s going on either.

The whole premise of the program is to be able to get an idea of insect pressures. Especially in the case of black cutworm, we can help try to forecast when the insect pressure could lead to insect damage and give advanced warming for scouting and just general awareness of different things that are going on in the field.

A sticky trap is one of the best ways to find out what is going on in your fields real time. It’s not always the easiest some days, but you’re definitely going to get some of the best information from it.