European Sawfly Larvae
Several varieties of pine sawfly larvae feed on many types of conifers across the United States. The European pine sawfly is one of the more common varieties. They feed on Scotch, Mugho, Red, Jack, and other pine trees in the eastern and southern U.S. The larvae look like caterpillars, but they are the young of a non-stinging wasp. The female adult will lay her eggs into a group of needles that are next to each other. She has a saw-like organ that makes a small cut into the needle in order to deposit her eggs. The eggs generally hatch before the new growth – often called ‘candles’ – has started. Therefore, they will feed on the older needles on one branch before moving to another branch. The larvae will reach about 1” in length, are dark green, and have a black head. In late May to early June, the larvae will drop to the ground and spin a cocoon. The adults emerge in early fall, mate, and lay eggs. The larvae are normally found in groups of about 30. They can quickly defoliate several branches on the tree. They generally do not feed on the newest growth, so the tree will survive, but in a weakened state.
Controlling European Sawfly Larvae
Selective pruning can control minor infestations of European pine sawfly larvae. If the larvae are small (1/8 to 1/4″ in length), then summer horticultural oils or insecticidal soaps can be used. Older larvae will need to be controlled using an insect control spray using carbaryl (Sevin), or similar type of material. Remember – always read and follow all label directions for responsible tree care. If damage had occurred the previous year, check for small brown spots from the egg-laying activities of the female on last year’s growth. Inspect the tree for the tiny larvae in early spring (early to mid April).
European Sawfly Behavior
The European pine sawfly larvae will rear-up in unison when disturbed. It is a fascinating sight to see the little green ‘soldiers’ all come to attention when one is threatened or touched. It is most likely a reaction to scare away a predator, such as a bird or parasitic insect. The quick response would appear to be threatening and would probably frighten most any attacker. It almost looks like the branch has come alive.
Types of European Sawfly
There are several other pine sawfly larvae that will do damage that is more extensive. The white pine sawfly hatches later in the year and will feed on both the new and old tree growth. It will feed on many of the same trees as the European pine sawfly. The white pine sawfly larvae are dark-colored and have rows of orange-yellow spots down its sides. It also has a black head. While the European pine sawfly has one generation, the white pine sawfly has two.
The red-headed pine sawfly will feed on the same pines as the other two, but will attack the Larch and the Norway spruce. It has a yellow body, a red head, and six rows of black spots along the length of its body. These destructive feeders are active in mid- to late summer and have one generation per year.
Good scouting of your landscape plants and a common-sense approach to tree maintenance and pest control will help keep these pests from doing extensive damage. Take time to inspect the plants in your landscape to inspect for insect and disease activity. Look for damage from last year and anticipate the same tree and lawn care problems again this year. Be prepared and treat the problems early so your plants will not suffer from pine sawfly, or many of the other pests, that inhabit your landscape.
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