Maple Leaf Miners: Introduction

by Carl Strang

 

Leaf miners are amazing insects, so tiny that they live between the upper and lower surfaces of leaves. They eat the succulent interior leaf tissues, and as they grow, the area they have depleted of these tissues expands to form a shape that is easy to see and is distinctive according to the insect species. Here are two common forms, linear mines in a cow parsnip (Heracleum) leaf, and blotch mines in a leaf for you to identify (note: this is a trick question! Plant identification given below).

 

Linear mines in Heracleum leaf

Linear mines in Heracleum leaf

 

Blotch mines in mystery leaf

Blotch mines in mystery leaf

 

 

There are flies and beetles that are leaf miners, but the ones I have been studying for more than two decades are minute moths whose caterpillars do the mining in maple leaves. The trees, at Maple Grove and Meacham Grove Forest Preserves, are either black maples (Acer nigrum), sugar maples (A. saccharum), or hybrids of the two. In the mid-1980’s, when I began studying leaf eating insects in these two forests, my attention was drawn by the large numbers of leaf miners in the understory maples on both study areas.

 

I was able to sort out five species of insects doing the damage. They include Caloptilia bimaculatella and C. packardella, of the moth family Gracilariidae. Their larvae begin with tiny mines which they soon leave, and their major growth takes place in folded, cone-shaped shelters (called here “boxfolds”) which the larvae construct at the tips of leaf lobes.

 

maple-leaf-mines-b

 

In the photograph, the boxfolds are unrolled and flattened to show how the green tissue has been scraped away by the tiny caterpillars’ mandibles. I have found both species on both study areas, and also two more members of the same family, Cameraria saccharella and Phyllonorycter clemensella. Cameraria form irregular blotch mines on the upper surfaces of the leaves, and Phyllonorycter produce tent-like mines on the under surfaces. I have not reared adults or identified larvae from the fourth mine type, a distinctive linear mine form, but it likely is the exotic (European) Stigmella aceris, of the moth family Nepticulidae.

 

There are a lot of questions that can be addressed in a system like this. For example:

  • Do the leaf mining species interact in such a way that they either avoid one another, occupying separate leaves as a rule, or do they congregate, clustering onto particularly attractive leaves?
  • These two study areas are separated by many miles of suburbs. Do the populations of the leaf mining species go up and down together on the different study areas (which might reflect responses to climate as it varies between years), or do they fluctuate independently (which might indicate biological regulation of populations)?
  • How does restoration management practice affect these organisms?
  • Do the moths have the same impact on the canopies of large trees as they have in the understory?

 

I’ll address these questions in future posts.

 

Mystery plant with blotch mine: did you recognize it as a rare, 4-leafleted poison ivy leaf? Probably most would regard this as less lucky than a four-leaf clover.

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