Each spring, about the first week of May, many pines are attacked by what seem to be large swarms of green worms. This is the European pine sawfly (Neodiprion sertifer) which was introduced into the United States in 1925. It is now a common pest of longer needle pines throughout the northeast and north central states.

It is not a true fly but rather belongs to a non-stinging group of wasps. Although similar in form, the larvae are not caterpillars.

Scotch (Pinus sylvestris) and red (Pinus resinosa) pine are most commonly attacked by this insect but Eastern white (Pinus strobus), mugo (Pinus mugo) and Austrian Pine (Pinus nigra) may also be susceptible.

 Life Cycle

The eggs of the sawfly larvae are tan to brown and half-mooned shaped. They may be found in rows of 6 to 8 eggs per needle on the previous season's growth. Newly hatched larvae have a shiny black head capsule and dark green body. When mature, they can be about 7/8 of an inch long. Their bodies will be gray-green with several light and dark longitudinal stripes.

 Eggs are deposited in a series of slits cut in the needle by the saw like ovipositor of the female in mid to late September. Larvae hatch in early to mid-May and begin to feed on the old needles. As they get larger, each larvae may eat entire needles and a group will strip all of the previous year's needles. They do not feed on the current year's needles at the tip of the branch.

 The full-sized larvae drop to the ground where they pupate. The adult saw flies emerge in September to mate and lay their eggs. There is only one generation per year.

Since they only eat the previous year's foliage, the European sawfly larvae are rarely fatal to the tree. In the rare case of massive numbers over several consecutive years, trees could be stressed enough to die during a drought or other additional stress.

 In the case of Christmas trees, however, it is important to control the damage of European sawfly since the loss of needles one or two season before a tree is sale able size may reduce its value.

 Control Alternatives

 On small trees in the landscape, control may be as easy as directing a strong spray of water onto the larvae and knocking them off the plant. Insecticidal soaps or horticultural oils at summer rates may also be used as an alternative.

 Foliar sprays of insecticides labeled for pine sawfly control are also affective in severe infestations. One application should be enough.

 The key is to look for the insect in early May as they begin to feed on the older needles. They are very easy to kill at this time and have done little damage.  

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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