HomeDave

Scarlet Oak (Slug) Sawfly



Species: Caliroa quercuscoccineae (Dyar) [Hymenoptera: Tenthredinidae]

Distribution:

This native insect is one of several in this genus that are commonly found in the eastern half of North America.

Hosts:

Pin oak and scarlet oak are preferred, but most oaks in the red oak group may be attacked. Oaks in the white oak group are not attacked by this species.

Damage:

Like most slug sawflies, the larvae have the habit of covering their bodies with a slimy material that may also contain excrement pellets. Occasional outbreaks can greatly skeletonize landscape and forest oaks. Completely skeletonized oak leaves drop prematurely and successive generations of this pest can skeletonize new leaves as they emerge. Normally, damage is an aesthetic problem.

Description and Life Cycle:

The 3/8-inch long, black fly-like adults emerge in mid-May to early June, after the oak leaves have fully expanded. The females insert their tiny, oval eggs in rows by slicing through the leaf epidermis with their saw like ovipositor. Upon hatching, the larvae crawl to the leaf undersurface where they begin to feed, often lined up side by side. The gregarious larvae are first black but they turn green with black head capsules as they grow. Within a couple of days, they have their characteristic covering of slime. After feeding for several weeks, the mature larvae are 1/2 to 5/8-inch long. The last larval instars become solitary and they crawl away to shed their skins and slimy coating. They then drop to the ground where they burrow into the litter and soil to spin a cocoon and transform into the adult. Two to three generations may occur in a season but the late cocoon forming larvae spend the winter instead of emerging. A generation can occur in 35 to 40 days.

Control Hints:

Normally, this pest is kept under control by several parasites and diseases. Even noticeable outbreaks are generally not dangerous to the health of the host oaks.

Strategy 1: Chemical Control - Use Insecticidal Soaps or Horticultural Oils - The 2% insecticidal soaps and 1.5 to 2% horticultural oils have been effective in managing these slug sawflies as long as contact with the larvae is made by the spray.

Strategy 2: Chemical Control - Insecticide Sprays - Several insecticides are labeled for control of sawflies in ornamental trees. Hold back sprays until it is evident that the oak sawfly population is reaching unacceptable levels. The larvae can be killed at any time that they are feeding on plant foliage.