Question
I live in Northern Nevada.  I have two locust trees that seem to be shedding sawdust.  The plants under the tree are covered every day.  I think something is boring through my trees.  Any idea what it could be?
Thanks!
Gail

Answer
This is a insect called the locust borer. The locust borer, Megacyllene robiniae (Forster) belongs to the beetle family Cerambycidae, commonly known as the longhorned beetles, a name which refers to the long antennae of most of the species in this group.

The boring activity of the larvae starts when the tree becomes active in the spring. The larvae bore up and in towards the heartwood, frequently returning to the opening to enlarge it. After reaching the heartwood the larvae bore down staying near the margin on the trunk and in the center of the branches. Larval tunneling in the trunk and limbs results in broken and dead limbs, weakened trees, excessive sprout production, and even death of the tree. Low vigor trees, damaged trees, and trees under environmental, drought, or nutritional stress are most likely to be infested. Trees of less than six inches diameter are most often attacked, while those larger than eight inches diameter are generally safe from attacks. A yellow sawdust is ejected when they reach the heartwood in late summer. As larvae bore deeper into the tree, they eject this sawdust- like material out of the burrow entrance.

Cultural practices that improve or maintain the vigor of locust trees will decrease the need for preventative or rescue applications of insecticides. Healthy, vigorous trees have little borer damage. During vigorous spring growth of the tree, larval mortality is at its highest, probably because of the high sap flow. Fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good.

If insecticides are required, sprays should be applied to the trunk and larger limbs. Treated portions should be thoroughly wetted with the spray. Spray with an insecticide called Merit, check with your local nursery/garden type store for an insecticide for borers.