|The Question: I noticed this little frog stuck to the outside of my exterior door about 11 p.m. The porch light was on and was attracting various “bugs” which I assume the frog was taking a keen interest in. I saw the frog jump from the door to this position next to the bug, which I assume looked like dinner? Anyway, what kind of frog and bug is this?
Submitted by: Chris, Cobb County, GA
The Short Answer: This is a green tree frog (Hyla cinerea) and the beetle is a pine sawyer beetle in the genus Monochamus, probably the Carolina pine sawyer (Monochamus carolinensis – thanks to the people at BugGuide.net for the ID). Both the Carolina pine sawyer and the green tree frog are common throughout the southeastern United States, so seeing these two together is not surprising.
Insect predators like the green tree frog often cleverly hang out where outdoor lights attract insects. That’s probably what this one was doing. It seems like this beetle might be a bit on the large side for this frog, but maybe not. One study showed that the green tree frog, like many other frogs, responds most to movement. So as long as this beetle stays perfectly still …
Destructive Invasive Species: The Carolina pine sawyer is one of more than 20,000 species of “long horned” beetles in the family Cerambycidae, so called because their antennae are often longer than their bodies. Many of the long horned beetles feed on trees, either living or dead. In the United States, the most well known long-horned beetle at present is probably the Asian long-horned beetle (Anoplophora glabripennis), which is considered to be a major –possibly catastrophic – threat to trees all over the country. Conservation and environmental authorities are conducting aggressive control programs to limit the spread of this non-native invasive beetle. For more information from the USDA, click here, and report any sightings of long-horned beetles by clicking here.
If you read about the Asian long-horned beetle and live in North America, you probably fear for your trees, and you might curse the processes that bring so many invasive animals and plants to our shores. But remember that the process goes in both directions. In Japan, for example, they curse the arrival on their shores of our pinewood nematode, a tiny worm with a very close connection to North American pine sawyer beetles.
The Beetle-Nematode Connection: Adult Carolina pine sawyers carry tens of thousands of the pinewood worms also known as the pine wilt nematode (Bursaphelenchus xylophilus). Nematodes in the Bursaphelenchus genus feed on fungi that grow on dying or dead trees. The worms are not particularly mobile, but they hitch a ride from dead tree to dead tree on insects like the Carolina pine sawyer. The pine wilt nematode has developed a further ability that others of its genus don’t seem to have, which is that it is able to grow and multiply in some live, healthy trees. More on that in a minute.
In North America, to which the Carolina pine sawyer and the nematode are native, the adult beetles feed on the branches of live trees. The beetles don’t seem to do any serious damage to a healthy tree and importantly, the pine wilt nematodes they carry don’t seem to do much damage. After feeding on live trees for about two weeks, the adult female beetles then find a dead or dying tree, cut a hole through the bark and lay their eggs. As they do so, the nematode worms jump ship (okay, crawl ship) and enter the tree through the hole made by the female beetle. Once in the tree, the worms multiply. Meanwhile, the beetle egg has hatched and is likewise eating the decaying tree tissue. When the beetle larvae reaches full size and metamorphoses into an adult beetle, the nematode worms crawl aboard the new adult beetle before it chews its way out of the tree and flies away. The adult beetle finds another dead or dying tree in which to lay its eggs, and the cycle begins again.
Notice, however, that the beetle and nematode don’t do much harm to healthy trees. And this is the story in North America for our native pines. However, the pine sawyers and their nematode friends can do great damage to non-native decorative pines like Austrian pines, Scotch pines and Japanese pines. When a pine sawyer beetle feeds on healthy trees of these species, it transmits the nematodes, which then multiply rapidly in the tree and can kill a tree in just weeks.
This is exactly what the pine wilt nematodes have been doing to pine trees in Japan since early in the 20th Century. It’s likely that that the nematodes reached Japan in trees imported from North America. Once there, it was spread by Monochamus alternatus, the Japanese pine sawyer, which previously had not been infected with the pine wilt nematode. The nematode is now a major problem in Japan, Korea, China and Taiwan and may now have gained a European foothold in Portugal.
To see a diagram of the life cycle of a Monochamus beetle and the pine wilt nematode, click here (about half way down the page).
In this country, we fear the potential for disaster that could be caused by the Asian long-horned beetle, but our own pine wilt disease – spread by Monochamus beetles– long ago became an ongoing ecological disaster in Asia, causing the deaths of uncounted millions of trees.
What Protects North American Trees: The situation in Asia is perfect for the beetles and nematode worms. The adult beetles feed on healthy trees, introducing the nematodes, which kill the tree, making it available for use by the beetle larvae, which then carry the nematodes to the next healthy tree. North American trees have developed some resistance to this process so that the nematodes only become established in trees that have been killed or seriously weakened by some other disease, insect damage or damage.
Special Thanks to Michelle Cram, biologist for the U.S. Forest Service in Atlanta, Georgia, USA, for her assistance and her correction of errors in the original version of this article.
Akbulut, S, & Stamps, W T. (2012). Insect vectors of the pinewood nematode: A review of the biology and ecology of monochamus species. Forest pathology, 42(2), 89-99.
Kikuchi, T, Cotton, J A, Dalzell, J, et al. (2011). Genomic insights into the origin of parasitism in the emerging plant pathogen bursaphelenchus xylophilus. PLOS pathogens, 7(9).
Freed, A N. (1980). Prey selection and feeding behavior of the green treefrog (hyla cinerea). Ecology, 61(3), 461-465.
How to Identify and Manage Pine Wilt Disease and Treat Wood Products Infested by the Pinewood Nematodes http://www.na.fs.fed.us/spfo/pubs/howtos/ht_pinewilt/pinewilt.htm – 10/8/2012.
An Overview of the Pine Wood Nematode Ban in North America –
http://www.forestpests.org/pinenematode/ – 10/7/2012.