Leafmining Insects Fact Sheet No

Leafmining Insects Fact Sheet No. 5.548 Insect Series|Trees and Shrubs by W.S. Cranshaw, D.A. Leatherman and J.R. Feucht* Leafminers are insects that have a habit of and/or its droppings (frass). Leaf spotting Quick Facts feeding within leaves or needles, producing fungi cause these areas to collapse, without tunneling injuries. Several kinds of insects any tunneling. • Leafminers are insects have developed this habit, including larvae of that feed within a leaf, moths (Lepidoptera), beetles (Coleoptera), producing large blotches or sawflies (Hymenoptera) and flies (Diptera). Common Leafminers meandering tunnels. Most of these insects feed for their entire of Trees and Shrubs • Although leafminer injuries larval period within the leaf. Some will also Sawfly Leafminers. Most sawflies chew are conspicuous, most pupate within the leaf mine, while others on the surface of leaves, but four species have larvae that cut their way out when full- found in Colorado develop as leafminers of leafminers produce injuries grown to pupate in the soil. woody plants. Adults are small, dark-colored, that have little, if any, effect on Leafminers are sometimes classified by non-stinging wasps that insert eggs into the plant health. the pattern of the mine which they create. newly formed leaves. The developing larvae • Most leafminers have many Serpentine leaf mines wind snake-like across produce large blotch mines in leaves during natural controls that will the leaf gradually widening as the insect late spring. The sawfly leafminers produced a normally provide good control grows. More common are various blotch single generation each year. leaf mines which are generally irregularly Elm leafminer (Kaliofenusa ulmi) is of leafminers. rounded. One subgroup of these are the the most important species, being locally • Insecticides applied when tentiform leafminers, which produce bulging common in several Front Range cities leafminers lay eggs are useful blotch-type mines that curve upwards where it develops on American, English for control of many leafminers. somewhat like a tent as the damaged and Siberian elms. Other species include: leaf tissue dry. Mining patterns often are hawthorn leafminer (Profenusa canadensis) combinations of the above, such as species associated with Crataegus crus-galli, C. that initially produce serpentine mines but persimilis, and C. erectus; birch leafminer terminate by making the enlarged leaf cavity (Fenusa pusilla) present in some plantings of a blotch mine. of white or gray birches; and alder leafminer Areas mined by insects die and dry out. (Fenusa dohrnii), a native species that Although injuries produced by leafmining develops in alder leaves. insects can be unattractive, it is rare for them Tentiform Leafminers. Larvae of to significantly affect plant health. Also, most several tiny moths (Phyllonorycter species) leafminers have important natural controls produce blotch mines in leaves that pucker which normally check populations before too when they dry out, somewhat resembling a much injury is done to plants. Injuries caused by leaf and needle mining insects can superficially resemble symptoms produced by leaf spotting fungi or other abiotic problems. They can be differentiated by pulling apart the blotchy area. If damaged by insects the leaf or needle will have a hollow area and may expose either the insect © Colorado State University *W.S. Cranshaw, Colorado State University Extension Extension. 3/96. Revised 7/14. entomologist and professor, bioagricultural sciences www.ext.colostate.edu and pest management; D.A. Leatherman, entomologist, Colorado State Forest Service; and J.R. Feucht, former Extension landscape plants specialist and professor (retired), horticulture. 7/2014 Figure 1: Spinach leafminer egg mass. pup tent. These tentiform leafminers occur Management of on willows, poplars, and cottonwoods, Leafminers of Trees hackberry and apple and leaf mines tend and Shrubs to be concentrated on the lower, shaded leaves. Probably two generations are Few, if any, leafminers pose any normally produced. Outbreaks are rare significant threat to the health of trees or because these insects are normally heavily shrubs. Injuries are cosmetic and treatment attacked by parasites and other natural decisions are based on plant appearance. enemies. Furthermore most leafminers have Lilac leafminer. Another small moth, numerous natural enemies that normally Figure 2: Elm leafminer injury. the lilac leafminer (Caloptilia syringella) well regulate their populations. Outbreaks, produces a blotch mine and then folds if they occur, are usually very short-lived. edge of lilac and privet leaves. A related However, exceptions to this can occur species, the boxelder leafminer, Caloptilia among the non-native species that are not negundella, produces similar leaf injuries to as well regulated by natural enemies in boxelder leaves. There are two generations areas such as Colorado where they have per year and the life cycle is likely similar to been recently introduced. Examples of non- that of the lilac leafminer. native leafminers are those found on elm Needleminers. Several minute moths (elm leafminer, European elm flea weevil), of the genus Coleotechnites have larvae birch (birch leafminer), and the tentiform that develop in the needles of conifers. leafminers of apple. Affected needles appear brown beyond the If controls are attempted with tunnels of the larvae. Most important is the insecticides there are two approaches to ponderosa pine needleminer (Coleotechnites consider. The first involves sprays applied Figure 3: Tentiform leafminer injuries to ponderosae) that has periodically produced to leaves that are timed to coincide with cottonwood. outbreaks in forested areas of ponderosa periods when egg laying occurs - usually pine. Related species occur in lodgepole shortly after leaves have expanded in pine, pinyon, and spruce. spring. Persisting contact insecticides Aspen leafminer. Delicate, winding can be used for this purpose, such as mines through the upper leaf surface of the various pyrethroids that currently aspen leaves are characteristic of another predominate for control of insects that small moth, Phyllocnistis populiella. The chew on leaves (permethrin, bifenthrin, feeding by the caterpillars that produce lambda-cyhalothrin, cyfluthrin, the mines produces insignificant damage deltamethrin), None of these will move and is notably mostly because they may systemically in plants so active larvae attract attention. within mines will not be affected. Sprays Poplar blackmine beetle. Large black of systemic neonicotinoid insecticides blotches in poplar leaves are produced (imidacloprid, dinotefuran) can provide Figure 4: Lilac leafminer injury. Photo courtesy of some control of these stages among Ken Gray collection. by larvae of a leaf beetle (Zeugophora scutellaris). Adults chew small pits in the leafminers that are beetles (Coleoptera) or leaf. Outbreaks are extremely rare and the sawflies (Hymenoptera). Neonicotinoids insect causes only minor leaf damage. tend to be poor in control of caterpillars, European elm flea weevil. Probably the larval stage of moths (Lepidoptera). the newest leafmining insect to establish in Alternately, neonicotinoid insecticides Colorado is the European elm flea weevil can be applied to the soil for root uptake. (Orchestes alni). The larvae make a leaf Imidacloprid (Merit, various generics) mine in elm that superficially resembles is widely available for this application that of the elm leafminer sawfly. The mine both through most nursery outlets and of the European elm flea weevil originates by commercial applicators. Dinotefuran from a leaf vein, meanders in a serpentine (Safari) is presently only available through form, and ultimately terminates in a leaf commercial applicators. blotch along the edge of the leaf. Adults are Figure 5: Serpentine leafminer on grape tiny beetles that jump which makes pits produced by small moth. in leaves, producing a lacy appearance of foliage when they are abundant. Leafminers of Vegetables grown, providing host plants for the insects. and Flowers Injuries most commonly occur in spring but there are two or more generations Columbine leafminers. At least produced during the growing season. two species of leafmining flies in the genus Phytomyza produce leaf mines in columbine. One produces blotch mines Management of while serpentine mines are characteristic Leafminers of Trees of the second species. Adults are tiny dark and Shrubs flies and females make leaf punctures with their ovipositor so that they can Controls have not been evaluated for the columbine leafminers but they are Figure 6: Serpentine mines produced in drink plant fluids. The presence of small cottonwood leaf. puncture marks is a indication of activity of likely able to be managed in the manner these insects and can be useful for timing of leafminers on trees and shrubs. insecticides applied for control. Furthermore, the feeding puncture wounds Vegetable leafminers. Several that the flies make can provide an early Liriomyza species of leafmining flies means of detecting their activity, thus make long serpentine mines through allowing proper timing of treatments leaves of flower and vegetable garden applied against the egg laying adults. plants. Normally these insects are very No controls for the vegetable leafminers well controlled by natural enemies and are recommended. Many insecticides have outbreaks are almost always associated with poor activity against these insects and use of

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