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| Gallery, larvae, and an adult beetle Wikipedia |
The Granulate Ambrosia Beetle (Xylosandrus crassiusculus) hitched a ride to South Carolina from Asia in the 1970's on packing crates. It has gradually spread across the Gulf States and has now been found in Missouri on the MU campus. It seems to prefer ornamental trees such as dogwoods and fruit trees, but can be found on some oaks and walnuts. There are 30 plus Ambrosia Beetles found in the US but this Asian visitor is more successful than the others and can kill trees when present in numbers.
The diagnosis is made by finding tiny white "toothpicks" extending out from the bark (see picture). These are columns of frass (insect poop) extruded when the beetle is boring its tunnel. This is just debris as the beetle doesn't digest wood for nutrition. Its sole food is the Ambrosia fungus that the female transfers into the tunnels.
There are several dozen species of Ambrosia fungi, all of which are only found in tunnels created by the Ambrosia beetle. Their relationship is pure symbiosis, each dependent on the other for survival.
According to Wikipedia there are around 3000 beetle species in many different families which use this same fungus feeding strategy. Many are not related and have developed this adaptation independently, an example of convergent evolution.
When the Ambrosia beetle larvae become adults, their next challenge is to go find a tree of its own. The problem is how do you pack your lunch when you only eat a fungus growing in a tree that you mother planted it in? The answer will be in Ambrosia Beetle- Part II, the next post.
* Dr. Starbuck's article is available at this site. Select Volume 17 No.2 and click on "Granulate Ambrosia Beetle: Another Exotic Pest of Ornamentals to Watch For" to download the PDF.