The cottonwood borer is limited in range to the southern half of the
United States. Hosts include cottonwood, poplars and willows. The adults
feed on the tender shoots of young trees causing them to shrivel and
break off. The larval stage of this insect tunnels in the inner bark and
wood at the base of the tree and may kill or severely weaken it.
[Illustration: Adult cottonwood borer.]
The adult beetles appear in midsummer. After feeding briefly on the
tender bark of the terminals the adults descend to the bases of host
trees where the female deposits her eggs in small pits gnawed in the
bark. Eggs hatch in about three weeks. The larvae bore downward in the
inner bark, entering a large root by fall. Larval feeding continues into
the second year as the larvae bore into the inner bark and wood. The
larvae transform into the non-feeding pupal stage and finally into an
adult in the summer of the second year thus completing a two year life
cycle. Adult beetles are 1¼ to 1½ inches long. They are black with lines
of cream-colored scales forming irregular black patches.
The best control for the cottonwood borer is to maintain a vigorous,
healthy stand. Slow growing, off-site plantings of host trees are the
most severely damaged. While some systemic insecticides have shown
promise, there is currently no registered chemical control method.