Chestnut and Invertebrate Extinctions

A few weeks ago I had the chance to speak to Dr. David Wagner at the University of CT about the functional extinction of the American chestnut and he commented with an anecdote I'd not heard before. He pointed out that the functional extinction of the American chestnut accounts for a significant percentage of the recorded invertebrate extinctions in modern times. In fact Dr. Wagner provided this qualified quote …

“American chestnut extinction correlates to the greatest invertebrate extinctions on earth in the modern era. That there are only 61 invertebrate extinctions in modern era … 41 in North America and of those, 5 are directly related to loss of chestnut.”
Dr. David Wagner

The five insects believed to be extinct as a result of the chestnut's demise (see the IUCN Red List) are Argyresthia castanella, Ectoedemia castaneae, Ectoedemia phleophaga, Tischeria perplexa, and Swammerdamia castaneae. In fact, seven are (were) red-listed as extinct but two of those – Synanthedon castaneae and Coleophora leucochrysella – have been subsequently found by Dr. Wagner and his team.

While the specifics are probably important, the general concept is truly monumental. Loss of a single species in an isolated ecosystem can have dramatic and unanticipated effects. In the most recent publication of the Annual Review of Entomology, David Wagner and Roy G. Van Driesche discuss some of the threats to rare insects by invasive species and the evidence is telling .

Since its discovery in Michigan in 2002, the Chinese buprestid Agrilus planipennis has killed more than 30 million ash (Fraxinus) trees in the northcentral United States (43, 122). If ash suffers the same fate as American chestnut (Castanea dentata), numerous Fraxinus specialists will perish. Wagner (168) identified 21 ash-feeding moths and butterflies potentially threatened by the beetle, of which five sphingids–Ceratomia undulosa, Manduca jasminearum, Sphinx canadensis, Sphinx chersis, and Sphinx franckii–are thought to be especially vulnerable.
Annual Review of Entomology 2010 55:565

This is a good reminder of the complexity of our ecology and the impact of a single foreign invasive pathogen. A bird lover, I always wonder how insect abundance affects birds. There is of course much more to the puzzle. If you have comments or other examples, please feel free to put them in the comments below.