An Outbreak of Sawflies!

An outbreak of pine sawflies defoliating pine trees in Lamar, Kaufman and Hunt counties have been reported, mainly on the loblolly pine. Although its identity has not been confirmed, it is likely one of the Neodiprion species of pine sawflies. Different species of sawflies cause periodic, widespread defoliation of pines throughout the southern states. The leaves (needles) of infested pines may be chewed down to the fascicles at the base of the needle bunches.

Sawflies are the only suborder of wasps, in the order Hymenoptera, that are plant feeders. They are greenish in color with dark longitudinal stripes and orange to black heads.

According to the Texas Forest Service entomologists, Joe Pase and Dr. Don Grossman, most affected trees should recover and re-leaf with no treatment. According to Pase, “The larvae feed mostly on 2nd year needles and leave the current year’s growth intact. The result is that few trees die from the defoliation. When tree mortality occurs, it is usually from attacks by pine engraver beetles (pine bark beetles) responding to stressed trees. Even then, few trees are attacked by pine beetles. Because the new growth on the trees this year has not progressed very far, the trees look especially bad, but I think most of them will come through OK – they just need a little time for the new growth to develop.”

If you feel that chemical treatment is needed, then applications of carbaryl or a pyrethroid insecticide such as bifenthrin or permethrin are suggested. Note that B.t. and spinosad are not effective against sawflies, since they are not true caterpillars.

There is usually more than one generation a year, so watch for additional feeding in late May or June. Trees that have been previously attacked may experience re-infestation by the 2nd generation. However, diseases and natural enemies usually keep later sawfly generations under natural control.

Sources: Joe Pase III, Entomologist, Texas Forest Service, jpase@tfs.tamu.edu and
Mike Merchant, Texas AgriLife Extension Entomologist, http://insectsinthecity.blogspot.com/.


Photo by: Pam Corder, Kaufman County Urban Forester.