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Mr. Smarty Plants - Leaf-cutter ants on non-native crape myrtle

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Thursday - May 08, 2008

From: Austin, TX
Region: Southwest
Topic: Non-Natives
Title: Leaf-cutter ants on non-native crape myrtle
Answered by: Barbara Medford

QUESTION:

We have a problem with cutter ants. I lose my entire Crepe Myrtle tree every year. All of the pest control personnel I ask do not have a solution. Can you please suggest something to eradicate these pests?

ANSWER:

When we first started researching this matter, we found that most sites on crape myrtle mention only mildew and aphids as major problems. So then we went looking for leaf cutter ants, and found that it is an enormous problem. Like fire ants, these creatures are imported from Central and South America and have no natural enemies in our area. This very comprehensive site from Texas A&M AgriLIFE Extension, Leaf Cutting Ants, has a lot of information that you should read. The pest control people you have been talking to probably either don't know how to approach the problem or realize it is bigger than they can easily control.

To quote from the above site:

"Defoliation by leaf cutting ants can resemble damage produced by several other leaf chewing insects, particularly sawflies and leaf cutting bees. Trees defoliated by the leaf cutting ant usually are within sight of an ant nest and the ants themselves may be seen carrying leaves. Foraging trails will be littered with pieces of leaf tissue that can be traced to a feeder hole. Considerable damage to a plant can occur in a few hours. Small- to medium-sized trees can be stripped in one night. One researcher in South America estimated that a large leaf cutting ant colony harvested approximately 13,000 pounds of leaves over a 6-year period. This same colony excavated 802 cubic feet of soil weighing over 44 tons."

First of all, let's make sure we're talking the right bug. Take a look at this page of Images of leaf cutting ants and see if that is what is going on in your yard.

We checked some websites on leaf-cutting bees, and don't believe this is your problem. This Wikipedia article on Megachilidae-Leaf Cutting Bees says that the bees are mostly solitary bees, and only cut the leaves for material with which to line their nests. They are considered excellent honey bees and not pests to be gotten rid of. And they're certainly not the bugs that are stripping your crape myrtle.

Next, we checked out sawflies, and found another Texas A&M site, Sawflies, which told us they are not flies, but related to wasps and bees, very plant specific in the type of plant they attack, and seem more inclined toward conifers.

So, we'll assume that it is indeed leaf cutters that are after your crape myrtle. The most recent information I found on those ants was that they were threatening pine forests as near as East Texas and on east into Georgia and Florida. They apparently choose one particular plant to chow down on, but the reason they take so many leaves is not for food and not for nest lining but for their own version of farming. They go back to the colony, chew the leaves and spit them out and on this base a fungus grows which is the only food of the ants, including the young. When a queen ant flies, she takes a "starter" from this fungus, establishes a new little hole, and plants her garden. Then, the workers come in and begin the fresh tunneling. Because they eat nothing but the fungi, putting out bait is not successful. Because they have such a large and intricate colony of underground tunnels, spraying down the holes in the conical mounds doesn't go far enough to do any real good.

So, you and probably neighbors have a major problem. We're assuming you live in a part of Austin that is in Travis County. Go to this website for the Travis County Extension Office, find a contact number and ask them if this problem is known elsewhere in the area, and what they recommend you do. We would recommend you find a licensed professional who will make whatever applications are necessary. We're afraid that cutting down the crape myrtles will not be any help, because the ants might just choose another host plant. In the meantime, you could always use the old home remedy of scattering diatomaceous earth (DE) on the mounds and the routes the ants are taking. It won't eliminate them, but it will give you some feeling of revenge, because the DE scratches their external protective covering, drying it out and killing them.

 

 

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