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Scale insects create sticky situation in St. Charles

Scale insects creating a gooey mess in St. Charles area

We're in a sticky situation in western St. Charles. Cars, driveways, plants, lawn furniture - everything outdoors - is coated with something sticky.

Just sap? Yes, and no. The substance raining from the trees is a by-product of sap. For three years in a row, small creatures called scale insects have infested woods in the St. Charles area.

The scale insects (scales, for short) suck sap from woody plants with their tiny, strawlike mouthparts. After digesting the sap, they excrete a sticky substance called honeydew. Sap in, honeydew out. Each tiny individual exudes copious amounts of this sugary stuff.

The tacky coating on plants is bothersome if you're working in the garden, walking barefoot on the grass, or sitting on a sticky lawn chair. But the problem doesn't end there. The honeydew attracts wasps and ants with a sweet tooth.

It also attracts mold - in particular, sooty mold. By late summer, the sooty mold casts a dark gray pale on everything in sight. Patios look dirty, wildflowers wilt, garden plants wither, and the autumn woods loses its glow.

Scale insects are indomitable little creatures. The type that plagues us in St. Charles are in a group called soft scale insects, specifically lecanium scales. Adult females are tiny - only 2-6 mm long - and easily overlooked. Females look nothing like insects; the head, legs, and antennae are hidden under a dome-shaped shell. They look like brown bumps on twigs and branches. Males are even smaller than the females. They're flat and transparent.

If you pry up the shell of a female in summer, you'll see what appears to be pollen. This is a mass of minuscule lecanium scale eggs. Each female can lay over a thousand eggs, which remain protected under her waxy shell.

Eggs turn into "crawlers," the larval stage of scale insects. The crawlers move around, usually migrating to the leaves where they fatten up on sap. At the end of the crawler stage, the larvae move back to the twigs and become adults.

The adults are voracious and suck sap like there's no tomorrow. Does this damage the trees? It can. Most damage occurs on already-stressed trees. Healthy, mature trees may withstand scales, but heavy, repeated infestations eventually weaken all the trees. This year, I notice significant die back in the upper branches of many oaks.

And, of course, there's that honeydew and the sooty mold yet to come.

The pressing question is, "What do we do?" The answer depends on whom you ask. There are companies who would love to sell you their services spraying insecticides. Unfortunately, aerial sprays are harmful to pretty much every creature they contact - including those who prey on scale insects.

This will, in turn, affect plants that rely on insect pollinators - lots of your ornamental plants, plants in your vegetable garden, and wildflowers. It will also affect birds who eat insects.

Plus, spraying pesticides for scale insects won't work unless you time it just right. Only the crawler stage is susceptible to chemical sprays, because the larvae lack the protective, waxy covering of adults.

You have to know exactly when the crawlers emerge. To be effective, every twig and branch must be treated. This is nearly impossible in heavily wooded areas.

Some plant specialists recommend a horticultural oil. This is a special type of oil that smothers adult scales. The challenge is, of course, applying oil to branches and twigs in trees that are 70-feet tall, and to cover hundreds of the afflicted trees.

This leaves the option of waiting it out - letting Mother Nature take her course. In fact, this is not such a bad option. Nature has deployed many troops in the battle against scale insects. Ladybug larvae are going to town on scale insects right now.

This week I've watched these larvae methodically crawling up and down scale-covered branches, indulging in scale meals all day long. Lots of hungry birds, like warblers, nuthatches, vireos, and orioles, glean scale insects from twigs. Grab some binoculars and watch these efficient predators at work - they're amazing insect-eating machines.

The coolest of all natural predators are probably the parasitoid wasps. There are a handful of species of these wasps that attack oak lecanium scales. Parasitoid wasps lay eggs inside other insects (or, in many cases, arachnids). When the wasp eggs become larvae, they eat their hosts from the inside out. Pretty gruesome - but, hey, it works for them! And it works for us, in controlling pests like scale insects.

A complication in the scale saga is that ants defend scales from predators. The ants have a hankering for honeydew, and they do whatever they can to keep it flowing. I watched ants in my back woods duking it out over a honeydew source. So if the ants are protecting the scale insects from predators, then what? Enter the flicker and its woodpecker cousins, who mine tree bark and ant nests for their own meals. These birds consume lots of ants, who might otherwise protect the scales, who would otherwise suck the life out of trees. Food webs are complex, and a tug on one strand affects all the other strands in the web.

The best thing we can do to battle scale insects and their ilk is to make our yards and woodlands inviting to their natural predators. There are more predator-prey interactions at work than we can shake a sticky stick at. I'm going to wait out this scale infestation, and watch the action. Biodiversity is the healthiest - and most economical - strategy all around.

•Valerie Blaine is the nature programs manager for the Forest Preserve District of Kane County. You can reach her at blainevalerie@kaneforest.com.

Honeydew, produced by scale insects that feed on sap, drips from the tree tops on everything below. Here, a drop of honeydew is caught in a spiderweb. COURTESY OF VALERIE BLAINE
Two ladybug larvae converge on scale insects. COURTESY OF VALERIE BLAINE
A ladybug larva feeds on scale insects, which are sucking sap from a hickory tree. COURTESY OF VALERIE BLAINE
A ladybug larva works its way along the buffet of scale insects on a hickory tree. COURTESY OF VALERIE BLAINE
A close look at the twig of a hickory sapling reveals scale insects crowding together, eating sap. COURTESY OF VALERIE BLAINE
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