Hungry, Redheaded Pests

Redheaded pine sawfly larvae dining on our mugo pine

If you have a mugo pine, it’s time to give it a look-over to see if it’s being eaten by groups of redheaded pine sawfly larvae.

We have one mugo pine that anchors a corner where two perennial beds meet in our back yard. A couple of weeks ago I checked it for the signs of the redheaded pine sawfly larvae and found nothing. When I was weeding and mulching on Thursday morning, I found three groups of the larvae busy eating the needles of our mugo.

What do I look for? First, I look for branches where needles seem to have been eaten. Then I look for—surprise here—the red heads of the sawfly larvae. A third sign comes after I shake the pine where I find the larvae and hundreds or thousands of bright-green fecal pellets, called frass, shower to the ground, sort of like a green snowfall in miniature.

Larvae in soapy water

What do I do when I find larvae? Since we have only one mugo pine, I pick them off with my fingers or tweezers, depending on the size of the larvae, and drop them into a bottle of soapy water. I find it easier to pick older, larger larvae with the tweezers and younger larvae with my fingers. Of the three groups I found, one was older, one was younger, and one was in between—so I used tweezers and fingers.

Some of the larvae didn’t appreciate my picking and went into their defensive mode, vomiting a pine-smelling resinous substance that they store to teach predators a lesson. I knew when my tweezers and my fingers suddenly were sticky and smelly.

Larvae frass, locally called 'green snow'

I stopped counting when I passed 100. I think I caught most of the larvae, but I’ll check back the next couple of days to make sure. I’ll also have to check back in August for a second generation. If I can’t control them by picking, I can spray with horticultural oil or a registered pesticide, but with one small Mugo pine, I haven’t had to do that yet

If you want additional information about this native pest and to see a short video of them in action, I recommend you visit Mike Raupp’s “Bug of the Week” website. At the Home page, click on “Archive” in the left column and then look for his posting of July 16, 2007. To access “Bug of the Week,” CLICK HERE.

And if you have a mugo pine—or other pines under 12-feet tall—better check now for this pest.