Origin:
This is a native species in North America.
Biology:
This pest is found throughout the U.S. and southern Canada wherever the host plants are found, and these include pear, cherry, apricot, plum, and some ornamentals such as hawthorn and ash. The larvae are capable of defoliating large areas of the trees, leading to reduced vigor in the tree, reduced fruit size and quality, and reduced bloom the next year. Female wasps deposit eggs in the tissues of the leaf, often in the upper branches, and two generations occur each year. The second generation is usually larger and progresses more quickly to the adult stage. The larvae often feed alone on a leaf but feed on the soft tissues, leave the leaf veins behind, and result in a skeletonized leaf.
Identification:
The larva of this wasp is unusual in that as it grows it covers itself with a dark slime that causes it to look more like a small slug than a wasp larva. Beneath this slime coating the larva itself is actually white initially and yellow as it matures. The adult wasp is small, only 0.2 inch long and a solid shiny black. While at rest it holds it wings folded over one another and flat over the top of the abdomen.
Characteristicts Important to Control:
Insecticides are effective but must be directed to the larvae wherever they are feeding on the foliage. Contact insecticide sprays can be used or a soil-applied systemic can be applied in advance of the presence of the damage on the leaves. The use of horticultural oils or soaps will also be effective but must be applied so that the larvae are thoroughly coated with the spray.
