Insect update: Good news for monarch butterflies, bad news for us on gypsy moths, Japanese beetles

  • "I'm seeing the kind of numbers that indicate a good start to the monarch year," says Doug Taron, who tracks monarch butterflies through the Illinois Butterfly Monitoring Network.

    "I'm seeing the kind of numbers that indicate a good start to the monarch year," says Doug Taron, who tracks monarch butterflies through the Illinois Butterfly Monitoring Network. Daily Herald file photo, 2003

 
 
Posted7/24/2019 5:30 AM

Doug Taron expresses the kind of cautious optimism you would expect from a conservationist who tracks a vulnerable, majestic creature.

So while he's not exactly uncorking the champagne yet, Taron is willing to say the monarch butterfly population is the one bright spot in what otherwise has been "sort of a depressing start" to the butterfly season in our region.

                                                                                                                                                                                                                       
 

"In general, butterflies have not been doing particularly well this year," he said. "I suspect part of the reason monarchs may be doing differently than other species is that we had so much rain and cold weather this spring, but the monarchs weren't here yet."

Monarchs migrate from Texas, arriving here around Memorial Day. Taron closely surveys their presence from the Bluff Spring Fen, an oasis for butterflies near his Elgin home. He will get a broader picture of the population this fall after analyzing data from Illinois Butterfly Monitoring Network volunteers.

So far, initial reports indicate a reassuring number of monarchs, the orange-and-black pollinator that has experienced sharp declines.

"I hope they can continue to have as strong of a summer as they seem to starting off here," said Taron, the network's director and the chief curator at the Peggy Notebaert Nature Museum in Chicago.

Here's a closer look at how monarchs and other, less welcome visitors to our gardens are faring after an unusually wet spring and topsy-turvy weather this summer.

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"I'm seeing the kind of numbers that indicate a good start to the monarch year," says Doug Taron, who tracks monarch butterflies through the Illinois Butterfly Monitoring Network.
"I'm seeing the kind of numbers that indicate a good start to the monarch year," says Doug Taron, who tracks monarch butterflies through the Illinois Butterfly Monitoring Network. - Daily Herald file photo, 2003
Monarchs

During the summer, monarchs enjoy three generations here and then begin an incredible migration south to Mexico. Taron and other surveyors are now seeing the peak of the second generation to emerge from the chrysalis for a two-week life span.

It's still too early to say whether the Butterfly Monitoring Network will record a repeat of what it observed in 2018, an "extremely strong year" for monarchs. The reasons then?

"Probably the same sort of things we're seeing this year: It was a wet spring down in Texas, and then we had a good growing season here," Taron said. "We didn't have a prolonged drought or anything like that, and that tends to be good for monarchs."

Also working in their favor? The lush growth of milkweed plants, said Andres Ortega, an invertebrate ecologist for the Forest Preserve District of DuPage County.

                                                                                                                                                                                                                       
 

"There's a lot of milkweed out there right now," Ortega said. "Big, robust plants, so there's a lot of food for the monarch caterpillars."

Monarchs lay eggs only on milkweed, and the caterpillars feed on the leaves, which is why the previous decline of the plants has taken a severe toll.

"Milkweed has a great advantage that it's not only very, very important for the monarch, but the flowers are a great nectar resource for all kinds of butterflies and other pollinator insects," Taron said.

Gypsy moths threaten the health of oaks and other trees.
Gypsy moths threaten the health of oaks and other trees. - Courtesy of Forest Preserve District of DuPage County
Gypsy moths

The DuPage forest preserve district will begin pulling traps of gypsy moths in about a month when the adult season ends to determine the levels of the invasive species that wreaks havoc on tree canopies.

"Just looking at the past five years, we're not seeing a significant variation in the population," Ortega said.

He expects that the fuzzy, insulated egg masses on trees over the winter provided enough protection from the brutal cold of the polar vortex.

"The hope was it being so cold, it would kill off a lot of them," Ortega said. "I don't have counts right now, but looking at all the other insects in the area, it doesn't seem the polar vortex actually had a significant impact."

The season for caterpillars -- and potential defoliation if the pests are abundant in that life stage -- has passed, and it's currently the breeding period for gypsy moths. The drab brown males fly, but not the off-white females that climb trees.

"So if you're looking for gypsy moth activity right now, I would recommend looking on any oak trees and seeing if you see any white moths crawling on the trees -- even though they have wings, they don't fly, so they'd just be crawling up and down," Ortega said. "That might be an indication of a gypsy moth infestation."

The egg cases can be too high to remove by hand in the fall and winter. Biodegradable oil sprayed directly onto the egg masses is generally the most effective treatment.

"The problem is if the caterpillar population gets so high that it's stripping the entire tree," Ortega said. "Even a healthy oak tree can only withstand maybe one or two defoliations. By about the third year, if that tree is stripped again, it's going to die."

Adult Japanese beetles are quite the nuisance, consuming leaves until they look skeletal. They'll eat leaves off roses and other ornamental plants.
Adult Japanese beetles are quite the nuisance, consuming leaves until they look skeletal. They'll eat leaves off roses and other ornamental plants. - Associated press, 2017
Japanese beetles

Adult beetles have emerged from turf soil, slightly behind schedule, said Julie Janoski, plant clinic manager at the Morton Arboretum in Lisle.

"They require heat for the larvae to come back to the surface, and they have to do that to pupate into the beetles," she said. "So the soil warming up more slowly than normal may have affected that."

The metallic green adults are hardly finicky eaters. In the category of ornamental plants alone, the beetles will feed off 300 different species, Janoski said. Favorites include roses, crabapple, cherry, grape and Linden trees.

"You'll see the damage on leaves," Janoski said. "They'll look like they've been skeletonized, like all the interiors eaten out, and the veins are left."

The females like to lay their eggs in moist soil in sunny areas from mid-July through early August.

"So if you go and plant some trees and shade your yard a little bit, you'll have fewer Japanese beetles," Janoski said.

The grubs also are quite the nuisance, consuming the roots of your grass. The plant clinic recommends following the timing, dosing and safety instructions of grub treatment products, but experts advise against using traps that use pheromone to lure beetles.

"They may actually attract more beetles to your yard than they're trapping," Janoski said.

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