Leafminers

I think many people believe that we already know what lives on this planet, and there is not much more to discover.  But there are still some curious explorers in this country that are making new discoveries, more than one could imagine.  Yes, we have names on many of the trees and birds and mammals found around the world.  But many tiny creatures, some in your own backyards, are waiting to be discovered.  Two of these taxonomic pioneers, Charley Eiseman and Julia Blyth, recently made a trip to the Edge of Appalachia to teach a class on leafminers.  Leafminers are not people that dig in the earth to find leaves, but rather tiny insects which, in the larval stage, mine (eat) through the fleshy inner cell layer of leaves.  Just as Lewis and Clark traveled the country keeping notes on new plants and animals they witnessed, Charley and Julia travel across this country's backyards and forests to discover new insect tunnels on leaves made by creatures still un-described in science.

Charley Eiseman showing the class an insect larva eating the inner portion of a leaf.

Have you ever seen a leafminer?  I bet you have.  Look closely at leaves on almost any tree, and you will probably find one.  Although you may not see the insect, the trail it leaves by tunneling through and eating the innards is evidence of its existence. These tiny insects can be larval moths, flies, beetles or even sawflies (wasp-like hymenopterans).  They have utilized the niche of the tiny space within the mesophyll of a leaf to eat, grow and presumably stay safe from predation.  But as in all things in nature, nothing is safe.  Many predators have honed in on these hiding insects and eat them. Parasitoids, many of which are wasps, can find and lay eggs on these sitting ducks, by piercing the leaf with their ovipositors. 

A tunnel mine of a moth, Phyllocnistis populiella.  Notice the dark line of droppings left behind in the tunnel.



A moth, Stigmella intermedia, on sumac, lays eggs on the leaf surface.  After hatching, the larva starts eating and you can see the tunnel grow wider as the larva grows until exiting the tunnel after pupation.

Enjoy this short video of a beetle larva feeding on the inner layer of an oak leaf.

Charley and Julia have keen eyes and did not have to walk far from the building before finding leaves that bear the mark of a leafminer.  They would find splotch mines or tunnel mines on grasses, tree leaves or any herbaceous plant.  One species of beetle that feeds on Virginia Creeper, Parthenocissus quinquefolia, was new to science a few years back.  This weevil is named Orchestomerus eisemani.  Eisemani of course, from Eiseman because Charley discovered this new species.  When they find a mine on a plant they have not seen before, they will take the plant home and wait for the critter creating the mine to pupate.  At that point they can identify the adult and record the culprit.

Charley Eiseman holding the leaf of Virginia Creeper with the mine of Orchestomerus eisemani 

Charley and Julia recording data of the mines collected during the class.

Within two days of our class, Charley and Julia had collected, identified and pressed the plants of over 100 specimens containing at least 80 species of leafminers.  All of these insects were new species additions for the Edge preserve collection.  Charley is working on keys to identify the leafminers.  Knowing the shape and size of the tunnel on specific plants can give you clues as to the species that created it.  So you may never see an adult Agromyza ambrosivora fly, but you can identify the mine on the leaf of an Ambrosia plant.  These leaves have been mounted and housed in the Eulett Center herbarium for reference. 

A few of the mounted specimens kept for reference.

Following are some examples of leafmines showcasing the artistic blotches and squiggly lines helpful for identification.

A moth, Astrotischeria astericola on aster

A fly, Aulagromyza orbitalis on Orange-fruited horse gentian,  Triosteum aurantiacum.

A moth, Cameraria guttifinitella on Poison Ivy, Toxicodendron radicans.

A moth, Coptotriche fuscomarginella on Black oak, Quercus velutina.

A moth, Ectoedemia platanella on Sycamore, Platanus occidentalis.

A fly, Liriomyza eupatoriella on white snakeroot, Ageratina altissima.

A fly, Liriomyza sp. on Ironweed, Vernonia.

A moth, Parectopa robiniella on black locust, Robinia pseudoacacia.

A moth, Phyllocnistis vitifoliella on grape, Vitis sp.

A moth, Stigmella prunifoliella on black cherry, Prunus serotina.

I think it is safe to say that you could count on one hand, if there are any other naturalists in this country that could have identified this many leafminers in such a short time.  They are a great team and have shared with us a whole new world living inside a leaf.  To see more of their work, publications, and blog, and to get information on how to obtain Charley’s new book, Leafminers of North America as well as his last book Tracks and Sign of Insects and Other Invertebrates (co-written with Noah Charney) click on the link here: http://charleyeiseman.com/leafminers/.

Posted by: Mark Zloba