Two years ago five elderly red maples were removed from my yard. These veterans had lost most of their crowns and one threatened to destroy my neighbor’s carport in the next windstorm. To soften the blow of losing these beauties, I replanted with an ‘October Glory’ red maple. This tree has spectacular color in autumn and is well suited to the soils and climate in Maryland. I moved my small October Glory from its large plastic container to its new home in the front yard. I dutifully removed all potentially girdling strings and bindings, used good organic soils to fill the hole, planted at the correct depth - not too shallow and not too deep, and carefully staked the tree to prevent windthrow. I kept my fingers crossed knowing that the years following installation are especially stressful for a tree as it struggles to establish a root system capable of fulfilling the water requirements of the plant. When I installed the tree, little did I know that Mother Nature was about to deliver one of the worst droughts to be seen in Maryland in many years.
Droughts wreak havoc on trees right along with floods and extremes of heat and cold. The reason for this has to do with the fundamental way trees go about their daily work. Trees transport water from the soil to the leaves where the magical process of photosynthesis combines the water with carbon dioxide from the air to produce sugars and the oxygen we breathe. Be sure to thank a tree today. Trees are marvelous chemical factories and use some of their sugar-derived products to grow while others are used to repair wounds and to produce compounds that help trees defend themselves from attack by many types of insects and diseases. You can imagine that prolonged periods of drought greatly curtail a tree’s ability to photosynthesize, grow, repair wounds, and produce defensive compounds.
As our drought deepened in May, I began to irrigate the sapling once or twice a week to compensate for the rainfall deficit. My worst fears were realized in June when a large vertical crack developed in the bark near the base of my now doomed October Glory. Despite my best efforts, the borers had arrived. Many kinds of beetles, caterpillars, and wood wasps bore into the shoots, branches, and trunks of trees. We met several of these in previous episodes of Bug of the Week including “The green menace - Emerald Ash Borer”, “The lesser ash threat? Banded ash clearwing borer”, "Beetles roasting on an open fire", and “Beautiful in yellow and black - The locust borer”.
Trees under drought stress are among the most vulnerable because their abilities to defend themselves and repair damaged tissues are compromised. Beneath the bark of my maple, larvae of a borer laid waste to a tissue called the cambium. The cambium is a layer of living cells that enables the tree to grow in girth. The cambium also generates cells that differentiate into tissues used to transport water and nutrients from the earth to the canopy and to conduct the products of photosynthesis from the leaves to the roots. Although it was too late to save my tree, in a fit of revenge I removed the loose bark and dug-out several fat happy borers with bellies full of cambium.
The shape of the larvae revealed that these were roundheaded borers. If uninterrupted, these larvae would have consumed cambium and other tissues nearby, and developed into pupae in galleries beneath the bark. In spring they would have emerged as glorious beetles called longhorned beetles. Longhorned refers to the exceptional length of the antennae of this family of beetles. Adult longhorned beetles are vegetarians and eat pollen, tender bark, and leaves. After dining and finding a mate, the female longhorned beetle “sniffs’ the air with her antennae to detect trees under stress and dying or those already dead.
Unfortunately for my October Glory, stressed trees
emit unique blends of chemical odors that are detected by the vigilant longhorned beetle. The subtle message tells the beetle that the tree’s defenses are compromised and the tree may not be able to put up much of a fight - an easy target. The longhorned female flies to the tree, deposits her eggs on the bark and, after hatching, the tiny borers enter the tree to conduct their nefarious work. Although I will never know the full identity of the culprits that did in my maple, I suspect that they were the larvae of red-edged saperda, Saperda lateralis. This longhorned beetle favors hickories, elms, basswoods, oaks, and maples that are stressed. A close relative of this beetle is the famous rounded headed apple tree borer, Saperda candida. This critter is a major of killer of trees in the rose family including apples, pears, crabapples, and hawthorn. Perhaps, with the benevolence of Mother Nature and a little luck, my next attempt to reforest my yard will meet with more success.
J.D. Solomon’s wonderful “Guide to insect borers in North American Broadleaf Trees and Shrubs”, USDA, was used as a reference for this Bug of the Week. To learn more about wood boring beetles, please visit the web sites below.