Tuesday, March 20, 2012

Flatheaded appletree borer

   The flatheaded appletree borer is a common pest of young pecan orchards. You rarely see the insect, but during early spring, you can easily spot the results of its activity in the crotch of a branch. In the photo at right, you can see a pile bark shavings created by the adult phase of the borer, a  buprestid beetle called  Chrysobothris femorate.  The adults chew their way out of the tree to escape from tunnels created by the insect's larval stage during the previous growing season.
   Even old exit holes created by adult flatheaded appletree borers are easily spotted near branch attachments. In the photo at left, note the oval shaped exit hole in the side of the tree at the point of a branch attachment. Once the adults emerge, they mate and female beetles begin laying eggs about a week later. Females beetles can lay as many as 100 eggs and search the tree's bark for deep crevices that offer some protection for the eggs. This female behavior is the reason larvae tend to develop at branch attachment points especially branches that have developed a bark inclusion.
    Eggs hatch in 15-20 days and the resulting larvae start to create tunnels under the bark feeding on the inner bark, cambium, and new wood. Healthy pecan trees fight flatheaded appletrees borers by producing excessive sap flow that can prove lethal to developing larvae. Trees weakened by stress often suffer the greatest damage from these borers, sometimes resulting in limb loss.
    The larvae are legless and can grow to 1.25 inches long. Several body segments just behind the insect's head are enlarged and flattened (photo at right). These segments are actually part of the insect's thorax, but appear to be a large flat head, thus the common name. Once larvae become fully developed they burrow deep into the wood of the tree to form a pupal chamber, where the insect over winters. Larvae pupate in the early spring and the adult beetles chew their way out as described above. 
    Although we find flatheaded appletree borers in most young pecan orchards,  the damage caused by this insect is usually not serious enough to warrant a control program. The best defense against borers is the keep your trees healthy with adequate nutrients, water, and weed control.