Calico scale (Eulecanium cerasorum) females spend the winter as small, crusty, flattened late instar nymphs (crawlers) stuck on plant stems. They don't look anything like their mature form and may be overlooked or misidentified.
They make their true identity known when they start pumping out impressive quantities of honeydew. The first image in this report, as well as the two images below, show something that I've never observed before. I took these pictures yesterday on honeylocusts (Gleditsia triacanthos) in southwest Ohio.
If you look closely, you'll see the shimmering droplets of honeydew are oozing from the femalesbeforethey inflate like balloons as they mature. In fact, some of the droplets obscure the source making it look like the trees are leaking sap.
These flattened females will eventually "puff up" and their characteristic helmet-shaped shells will display the starkly contrasting calico pattern of black-and-white markings that gives this scale its common name. I've only ever observed heavy honeydew production during the puffing-up phase, not while the females remained flattened on the stems.
Calico scale is a type of "soft scale" meaning their shells can be easily crushed. In fact, this soft scale can be handily removed from tree stems using a scrubbing pad or scrub brush. It's an effective management method for small trees and preserves natural bio-allies such as lady beetles and other predators that target this sucking insect.
Origins of Scale Poo
As with all soft scales, calico scale adults and nymphs (crawlers) feed by inserting their piercing-sucking mouthparts into phloem vessels to withdraw sap. They extract both carbohydrates for energy and amino acids to build proteins. However, the sugary sap contains a much higher percentage of carbohydrates by volume compared to amino acids meaning the scale must remove a huge amount of sap to extract the quantity of amino acids required to meet their needs.
They discharge excess sap from their anus in the form of a sticky, sugary, clear liquid called "honeydew;" a polite name for the liquid scale poo. The honeydew drips onto the leaves and stems of infested trees as well as understory plants, sidewalks, lawn furniture, parked cars, stationary entomologists, etc. My hat, shirt, glasses, and camera have become speckled with sticky scale poo goo during past visits to heavily infested trees.
Black sooty molds quickly colonize the honeydew imparting a black veneer to stationary objects. Despite its unsightly appearance, the sooty molds cause no direct harm to plants other than possibly interfering with photosynthesis.
What's Up Next?
The females will continue to spew honeydew as they mature towards egg production. Each female can produce more than 1,000 eggs, so populations can build rapidly.
Calico scale females die after producing their eggs and quickly turn reddish-brown and appear deflated. The 1st instar crawlers that hatch from the eggs migrate to the underside of leaves where they attach themselves to veins. They suck fluid from phloem vesicles and drip honeydew; it's a family business.
A Host of Calico Problems
Calico scale has a wide host range. In fact, few landscape trees in Ohio other than conifers are beyond the reach of this Asian native. Here is a partial A-to-Z list of possible hosts: buckeye, crabapple, dogwood, elm, hackberry, hawthorn, honeylocust, magnolia, maple, oak, pear, redbud, serviceberry, sweetgum, tuliptree, poplar, witchhazel, yellowwood, and Zelkova.
Fortunately, as with most soft scales, calico scale is seldom a direct killer of established landscape trees. But heavily infested trees may suffer branch dieback and the accumulated stress caused by substantial sap loss coupled with other stress-inducing conditions may kill trees. So, the best first step in scale management is to resolve other issues that may affect overall tree health. I've frequently observed large, heavily infested honeylocusts that are planted in good sites showing no obvious symptoms. Just don't park your car beneath them.