Palm Tree Borers

Identification

• The giant palm borer (Dinapate wrightii) is a member of the Bostrichidae family and is typically a secondary pest that attacks already stressed palm trees. Adults are large brown or black beetles that grow up to 2 inches long and carry no hair on top of their body, but a collection of gold hair underneath. Primarily active at night, adults appear in midsummer with females chewing into the trunk near the base of leaves. Here, they are met by males and mating commences.

Features

• Palm borer larvae take on a yellowish color and bore into the trunk of the palm tree where they live for several years. When nearing adulthood, the larvae pupate near the surface of the trunk and then chew their way into the open. Sometimes, they back out of holes because their abdomens have become larger than their heads. The presence of both adults and larvae will be noticed by the large holes they leave behind, each approximately 1/2 inch in diameter.

Considerations

• The chewing of the beetle is so distinct that other insects use the sound to find the palm borer and devour them. Spiders and bees often use vacated holes to build their own nests. The incessant feeding by the palm borer over the course of years weakens the tree immensely. As the trunk is filled with holes, it becomes more vulnerable to windy conditions and may eventually fall. The first symptoms of distress from the tree are a yellowing of the palm fronds.

Management

• The California fan palm (Neowashingtonia filifera) is the preferred tree of choice for the giant palm borer, but the insect is known to infest other varieties of palm such as the date. The best practices for management include keeping palm trees healthy and providing proper cultural care. Dead palms in which the borer have lived should be destroyed. In most instances, the giant palm borer will only inhabit older palms, tending to leave younger, healthier palms alone.