News release: Pine Sawflies

Tim Baker, MU Extension Horticulture Specialist
102 N. Main, Suite 1, Gallatin, MO 64640
660-663-3232, bakert@missouri.edu

Release date: June 27, 2013

Title: Pine Sawflies

For every plant that exists, I think there is an insect that will eat it. When it comes to plants that we grow to consume, it seems that there are literal armies of insects out there to destroy our carefully cultivated crops. Well, that’s understandable.  If it tastes good to us, surely it tastes good to the bugs.

But what about the plants that would normally be unpalatable to us?  Surely no insect would be interested in them, would they?

I think so, in most cases.  Take pine trees for example.  I wouldn’t think pine needles would be very tasty, and they might even be bad for you.  But as you may have guessed from the title of my column, yes, there is an insect that loves to eat pine needles.

That insect is the pine sawfly, which is classed in the same insect order as ants, bees, and wasps (Hymenoptera).  The larval stage looks like a caterpillar, and often has stripes. These insects can strip the needles from pine trees in short order. If the number of pine sawflies is high enough, they can completely defoliate a pine tree.

While the larvae may look like caterpillars, they are not in the same order as butterflies and moths (Lepidoptera). Many organic gardeners use biological insecticides such as BT (Bacillus thuringiensis) which work well against lepidopterous insects. However, BT will not be effective against pine sawflies.

To control pine sawflies, you may not need to do anything. Pine sawflies have natural enemies that may keep them under control. Diseases, starvation, and unfavorable weather may help keep their numbers down as well.

However, at times, they may occur in such high numbers that you will need to spray an insecticide to keep your pine tree from being defoliated.  Products such as carbaryl (Sevin) should control them, but be sure to read the label carefully before you purchase and use any product.

The problem for most homeowners is how to spray a tall tree.  Most spray equipment will not reach the heights needed to spray a mature tree. You may need to call a professional arborist to perform this service. Remember, however, that pine sawflies may have up to two generations per year, so a repeat spraying may be necessary.

Images

Pine sawfly larvae on a tree, showing bore holes. Click for larger image
Pine sawfly larvae on a tree. Click for full size, print-quality photo (4.5 mb)

Close up of pine sawfly larva.  Click for full-size image
Close-up of pine sawfly larva. Click for full size, print-quality photo (1.3 meg)