Redheaded pine sawfly larvae were found on Scotch pine in McLeansboro in southern Illinois on June 12. This sawfly feeds primarily on two- and three-needle pines, and is particularly common on Scotch, jack, and red pines. They can also feed on five-needle pines, Norway spruce, and larch growing near two- or three-needle pines.
The larva is about an inch long when fully grown, has a red head, and is yellow with several rows of black dots. As with all sawfly larvae, it has more prolegs than caterpillars have (caterpillars have five or fewer pairs of prolegs). This species has seven pairs of prolegs on its abdomen, as well as three pairs of true legs on the front end of its body. The larvae feed on the needles, defoliating branches or trees. Because all of the needles can be eaten, stripped branches or trees are likely to die.
Full-grown larvae drop to the ground where they pupate in a silk cocoon and emerge for a second generation in late August through September. In the southern U.S., three generations per year can occur. Winter is spent as a prepupa in a cocoon on or in the duff under trees. Thus, removing fallen needles and debris beneath infested trees in the winter should eliminate many of the mature larvae. The prepupae pupate in the spring to emerge as adults a few weeks later. Some prepupae may lie dormant through two or three seasons before emerging as adults.
This insect is spotty in occurrence and is usually found in the southern third of Illinois as well as in north central and northwestern areas of the state. Look for these larvae now in southern Illinois and be watchful in northern Illinois in about two weeks.
Control can be achieved with many chemical insecticides. Remember, this is not a caterpillar, and therefore will not be controlled with Btk.