by Kathy Rusniak

Created on: February 03, 2009   Last Updated: February 26, 2009

The emerald ash borer, or Agrilus planipennis, kills ash trees through a slow process of strangulation of the trees' circulatory systems. Vital water and nutrients that provide the limbs and leaves with hydration and energy are blocked by the colonization and growth of these tiny green pests. Likewise, nourishing sugar supplies are cut off from their ultimate destination in the roots. With dwindling nutritional support from below, the branches and leaves slowly begin to die off. With less and less of the sugars produced in photosynthesis to feed the tree roots, they begin to die as well. To gain a clearer understanding of the problem, it is important to look at the basic function and structure of a tree as well as the life cycle of the emerald ash borer to see how the habits of the ash borer interfere with the ash tree's vital physiological processes. Another important consideration is that the Asian pest's habits also lead to easy and often unwitting spread of infection and general ash tree population decline.

All trees have several layers of tissues in their trunks that have unique functions. A cross section through the body of a tree trunk, starting from the outside and traveling inward, would reveal the bark (made mainly of cork and cork cambium), phloem, cambium, xylem and finally the woody core. The bark is the older cork tissues that get pushed outward as new cork is produced. This origin is responsible for the cracked appearance of bark, whose dried and tough surface serves to shield the tree from outside forces.

The phloem itself transfers newly made sugars from the leaves at the tips of the branches in the canopy, all the way down to the tree roots deep underground. Conversely, the xylem draws up water and nutrients from deep below ground at the tips of the most microscopic root hairs all the way up the trunk and into the canopy to feed the tree's growing and food producing appendages. Between the phloem and the xylem, the cambium is the generative tissue that produces the new tissues of both the food and water transporting systems, growing one type of tissue in each direction simultaneously. The inner core of the trunk is made of the growth tissues of past years the tree has outgrown and so have slowly gone dormant. These inner core layers are the rings of the tree that most people are familiar with and also make up the woody portion of the tree used for furniture and raw construction materials.

At the start of the ash beetle's life cycle, the spaces

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