The Value of Christmas Trees

"...there is no reason why the joy associated with the Christmas evergreen may not be a means of arousing in the minds of children an appreciation of the beauty and usefulness of trees; and keen appreciation of the beauty and usefulness of trees is a long stop toward the will to plant and care for them (Arthur Sowder, US Forest Service, 1949)."

Thursday, January 5, 2012

Parasitic Wasps on Scale Infested Trees

This photo depicts Frasers set up to see how likely elongate hemlock scale crawlers will come off of cut trees. The yellow sticky cards were used to trap the crawlers. But something more interesting was found. Wasps!

These are predatory wasps, probably Encarsia citrina though I didn't have them positively identified. They are very small. The following photo has both a wasp (on the right) and a crawler (bottom left) on it. You can see the wasp is only a bit larger than the crawler. 

The wasps lay an egg in a scale and it develops inside. When the wasp emerges, it leaves a hole in an otherwise empty scale casing. You can see these sometimes when looking at scales on trees.

I put a photo of a wasp that hadn't emerged yet from inside of a scale on my October 6, 2011 post "Last Treatments." In that post, I made the comment that when you don't add Talstar or Asana to Safari, you see a lot more parasitized scales. 

Interestingly, I only found these wasps on cards put in the two untreated trees. The tree that had been treated in the fall had no wasps in it. That made me curious to see how readily wasps are found on trees following different treatments. I plan on setting up some branches inside a warm location over the next few weeks to see how many wasps appear on sticky cards. Perhaps this can shed some light on how we can control scales without creating conditions for a quick rebound by killing off all of our natural enemies.

These wasps are very small. You would never see them flying around in your trees. But they are giving you free pest control. That's why its so important to only use an insecticide when you really have to. 

Another view of one of the wasps. 

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