First chewed needles are visible in mid- to late April. Sawfly larvae are easily killed by most broad spectrum insecticides, insect growth regulators, botanicals, or insecticidal soap or oil. Most effective control is achieved when pesticide is applied early in the season when sawflies are young. After sawflies are one inch long they stop feeding and construct a pupae. Applications of insecticide at this time are no longer needed.
Sawflies regularly suffer from a lethal virus-like disease that greatly reduces their number.
If you notice larvae that are hanging limp from pine needles there is no need to apply an insecticide. This virus-like disease is not likely to be commercially available in the near future.