Skeletonization sounds like a good descriptive term, but this word can represent very different conditions in the mind’s eye:
1) Surface feeding (Figure 1), which leaves a window-like effect of thin leaf tissue (caused by echelons of oak slug sawfly larvae)
2) Foliage stripped (Figure 2) so that only main veins remain (caused by night-feeding May beetles)
Different types of feeding by very different insects.
Oak Slug Sawfly
Oak slug sawflies are the larvae of small, plant-feeding wasps that can strip the surface tissue of scattered oak leaves. Generally, the damage is spotty with no consequence to healthy, established trees. There may be 3 generations during the summer, but control is rarely warranted.
May beetles (Figure 3) are brown-to-black beetles that emerge suddenly from lawns and grassy fields during May and June, especially after rains have softened the soil. Several beetle species are involved. They feed at night and prefer the foliage from most of the common oaks, as well as birch, elm, hickory, and walnut. Entire leaves may be eaten or petioles may be cut so leaves drop to the ground. These beetles often feed on, but rarely strip, ash, fruit trees, hackberry, locust, Lombardy poplar, maple, plum, and willow.
May beetle larvae are white grubs that have fed on grass roots for several months, or even several years, before emerging as adults to reproduce. Damage often is worse on trees near expanses of turf.
As with the sawfly, control is not needed on medium to large healthy trees. New trees in the landscape may befit if damage is caught early. A foliar spray of tree and shrub products containing any of these or similar active ingredients can be used to protect the remaining foliage: bifenthrin, carbaryl, cyfluthrin, malathion, permethrin, or spinosad. These insecticide names can be found in the Active Ingredients box below the brand name on the product label.
By Lee Townsend, Extension Entomologist