Additional information from the University of Massachusetts:

"Imported Currant Worm (Nematus ribesii): The full-grown sawfly larva is 3 inches long; it is green with yellowish ends, has a black head, and is covered with black spots. Shortly after the leaves are out in the spring, the worms feed first in colonies and later singly, voraciously stripping the plants of foliage. A second brood occurs in early summer, and a partial third brood may appear depending on the weather. If numerous, they can strip a bush of its foliage in a few days.

Management: Monitor for and remove leaves harboring eggs by hand. Watch for larvae starting just after bloom as the fruits start to enlarge. Cultural control involves being observant of growing conditions and keeping plants vigorous. Insecticide applications may be made as soon as larvae are found feeding on the leaves."