eGarden © 2006 Ed Mues

From The Garden of Ed. Submitted for publication in The Towne Crier on April 19, 2006

Two Caterpillars Worth Knowing.

I stress the "worth knowing". Grabbing the can of "Raid", which a neighbor did last year, is not the best option. It is harmful to the environment: that includes you and me, the beneficial insects, the air quality, and the trees it is sprayed on. It is neither cost, nor time, effective.

These two caterpillars can sometimes cause serious economic damage. They hatch from eggs laid last year and appear in the spring. They awaken ravenously hungry. They are minute. I hatched three different broods of eggs at monthly intervals this past winter indoors, and they were all about 3 millimeters long on emergence. These pests worth knowing attack ornamental trees and shrubs, as well as valuable forest trees. I'm writing about them because there is the potential for significant defoliation this year. They will be appearing very soon.

This past winter is characterized by especially mild temperatures, one of the warmest Januarys on record, and one of the driest Marches on record. Furthermore, there was virtually no snow pack for the entire winter, even after a couple of moderate snow events. As I write this, we are still in a drought. I'm hoping we get some relief in the coming weeks. There is little moisture in the ground. These factors suggest that our trees are probably stressed. January's warmth surely challenged their dormancy. The ever present acid rain adds to the stress equation, as does the excess fertilizer runoff that is endangering the biological health of the very soils they rely on for support.

Within the next couple of weeks you will begin to notice small silken webs where branches fork. It is the protection for the Eastern Tent Caterpillar, a native insect. You will see these just as new leaves begin to unfold. They collect in the crotches of a tree and spin a noticeable mass of webs. Look in particular at wild cherry, apple and crabapple trees, but they will attack several others. As the caterpillars continue to eat leaves and grow, they carry their silken thread with them and the "tent" of webbing expands. Removing and destroying the tent-like nests is an effective control. These caterpillars eat the leaves and are sheltered by the nest. They do not ascend and descend the trees they inhabit. If the larvae are still young, less than an inch in length, spraying the leaves with Bt (Bacillus thuringiensis) is the control of choice. Bt is a naturally occurring microbe that controls many harmful caterpillars and is harmless to humans, pets and beneficial insects. They must eat the Bt sprayed leaves to be killed. Does this raise the question I've brought up before? I said, "Everything has a right to live", if I recall correctly. So be it. You decide.

The egg masses of the ET caterpillar are distinctive and usually easy to reach. They are like a shiny brown tube wrapping around a twig. The whole thing is about as thick as a pencil. They have been there since last summer when the adult moth laid them. Scrape them off easily with your fingernail. They feel like and resemble Styrofoam.

Egg hatch coincides with the blossoming of shadbush, star magnolia, Japanese quince and bridal wreath (spirea). In our area this is usually in the last weeks of April and first two weeks of May. The warmer the season, the earlier it might be. The adult caterpillar is 2 to 2 1/2 inches long, is black with a continuous white stripe along the middle of the back, bordered on each side by a broken reddish-brown line. Each segment has a small, vertical blue mark on the side.

Nearly coincidental, or at most, a couple of weeks later, an even more serious pest hatches from very different, but still noticeable egg masses. It is the, an alien invader from Europe, accidentally introduced to North America. It is one of the most important forest pests of the Northeastern United States. They will eat as many as 500 different species of plants. Oaks are the favorite. Stressed deciduous trees and shrubs that are defoliated two years in a row can die.

Evergreens can die in a single year. My property was hit very hard last year. Thanks to some ample rainfall everything leafed out again. Egg masses, however, are abundant high up in trees, on rock outcroppings, woodpiles and lawn furniture. I purchased firewood recently, and I received an unexpected guest: more moth eggs. They are buff colored, feel like velvet, and are about 1 1/2 inches long by 3/4 inch wide. These are the ones I hatched indoors after collecting in December, January and February. About a month at room temperature was all it took. They are ready and waiting, and in a few weeks, they may begin their unwelcome work.

Fortunately, Mother Nature has provided us with some help against these potential attacks. Nine parasites (wasps and flies) have been identified that lay their eggs into the eggs of the GM eggs. The parasites usually control about twenty percent of the hatch. It's a small, but not insignificant, help.

Our most important ally is the fungus, Entomorphaga maimaiga. Its spores are found on the ground in woody debris and leaf litter. A few days after hatching, the young larvae eat the leaves at night and descend the tree before daybreak to seek protection. They do this by hanging and descending on silken threads. Breezes can easily blow them to other trees. (More mature caterpillars have to climb down and back up.) While on the ground, if the spores are present, the GM caterpillars come in contact with the spores, contract the disease, and are often found on tree trunks shriveled and dead before they reach maturity. Crucial to the success of the fungus in controlling the caterpillar numbers is the amount of rain. The fungus and spores can only proliferate if there is a wet spring, especially in the month of May. A wet, mild April may be helpful. If their population is not checked, expect trees to begin to take on the look of winter: skeleton trees.

Checking the population calls for other options. Spraying programs can be initiated. If the GM caterpillars are still young (3/4 of an inch) and the spring has been dry, Bt, mentioned above, is the preferred material to spray if conditions are appropriate. Spray the foliage of your favorite landscape plants to protect them. Trees are out of the question, without hiring professionals. Mature GM caterpillars are slate colored, about 2 to 2 1/4 inches long. The back has two rows of blue spots (five pairs) followed by six pairs of red spots.

Another non-chemical option toward controlling more mature GM caterpillar populations requires a little hands-on mechanical work. Wrapping the trunks with a protective band to trap ascending caterpillars can protect oaks and other valuable trees, and even landscape favorites. Burlap flaps, duct tape applied sticky side out, and some very sticky material, such as Tanglefoot applied to some landscape paper or tree wrap are three methods that can be used effectively to trap the caterpillars on their return trip to feed on the foliage. Care must be taken not to damage the tree trunk. Collect trapped caterpillars daily. Scrape into soapy water. Don't crush with your fingers, as many people are allergic to the hairy spines.

The world has come along at an astonishing pace. Today I received a call asking me for my "physical address". I almost answered, "Where the Gypsy Moth eggs are", but thought better of it. I hope I've given you a little bit of useful information about these soon to be seen, leaf eating, moth caterpillars. So much more is available. Don't hesitate to drop me a line if you need more information, or call Cornell Cooperative Extension at 292-6180.

From The Garden of Ed. Submitted for publication in The Towne Crier on April 19, 2006

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