Leaf-Mining Insects - John A. Byers

Leaf miners form a natural rather than a taxonomic group of insect species that are adapted to a special type of environment.

Definition: A leaf miner is a species, the larva of which lives and feeds for a part of all of its time between the epidermal layers of a leaf. The mining insects have habits that grade into gall making and deeper plant boring as well as external feeders and scavengers. There is little difference between a borer and a miner except that the borer feeds deeper in the tissues of plant. Bark beetles, that mine under the bark in the phloem and cambium layer could be considered miners or borers. The codling moth, typically boring in fruit of apples, sometimes mines the surface of the fruit. The Diptera family of Agromyzidae also show habits of both leaf mining and boring. Agromyza youngi mines the petioles and flower stalks of dandelion flowers as well as its leaves. Some leaf-mining species also make galls. Agromyza laterella (Agromyzidae) produces a gall on a young tender iris leaf but a mine on mature leaves. In the genus Agromyza, some species like tiliae, schineri, and websteri are gall makers of citrus, poplar, and wisteria (respectively), simplex is a stem borer of asparagus, aeniventris and virens are pith borers, amelanchieris, aceris, and pruinosa are cambium miners, laterella makes both leaf mines and galls, while most other species are largely leaf miners of herbaceous and woody plants.

The family Cecidomyiidae in the order Diptera (flies) have many species that intergrade between gall making and leaf mining. The tulip spot gall, Thecodipolosis liriodendri, is only a slight thickening of the leaf while the tar-spot gall, produced by a species in the genus Asteriomyia has even less thickening is little more than a leaf mine. The boxwood leaf miner, Monarthropalpus buxi, makes a leaf mine but the surrounding tissues proliferate. None of the Cecidomyiidae, however, produce long leaf mines typical of the Agromyzidae flies.

Some leaf-surface feeding insects may appear like leaf mines. Some Chironomidae (Diptera) dig grooves in leaves, removing the upper epidermis and packing the channels with frass. Many larvae of the order Lepidoptera (moths and butterflies) have similar habits.

Leaf miners attack nearly all plant families. The insects can mine plants with milky juices, poisonous to higher animals, and even aquatic plants. Leaf miners are most numerous in the tropics but are still widely distributed in the temperate zones. However, miners are rare or nonexistent on high mountain tops or Arctic zones where plants occur. Insects of four orders have evolved the leaf-mining habit: Coleoptera (beetles), Lepidoptera (moths), Diptera (flies), and Hymenoptera (sawflies), or in other words in orders with complete metamorphosis and the highest degree of specialization. The adults are able to fly and to select the appropriate host plant for their larvae. Only the larvae are able to live in the interior of leaves since the adults are winged and therefore disperse, find host plants, and mate. Most leaf-miner adults are small and can be very beautifully colored.

Â© by John A. Byers