NC State Extension Publications

Description and Biology

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Locust leafminers, Odontota dorsalis, are small, elongate, flat beetles, about ¼ inch long. The head is black and the wing covers are orange with a broad black or brown stripe down the center. The wing covers are deeply pitted and have three long ridges each. Full-grown larvae are yellowish, flat, and slightly longer than adults. Locust leafminers have one or two generations per year. Locust leafminers overwinter as beetles in bark crevices and leaf litter. They emerge in spring about the time leaves start to unfold to feed on the lower leaf surfaces where they also lay eggs. The eggs overlap like shingles in groups of three to five and are cemented together by excrement. Upon hatching, the tiny new larvae feed inside that leaflet. Later the larvae leave to mine other leaflets. One larva may mine several leaflets before it matures. Larvae pupate within the translucent mines in July. There are two generations per year. Several parasites and predators attack the locust leafminer, which may explain why it does not maintain large populations in one area for long.

Locust leafminer adult beetle

Locust leafminer adult beetles are yellowish and flat.

Locust leafminer eggs

Locust leafminer eggs are laid on the undersides of leaves.

locust lfmner larva

Locust leafminer larvae are usually found inside their mines.

locust lfmn dam

Locust leafminer damage resembles frost or drought damage.

locust lfmne dam close

Locust leafminer mines are translucent and whitish but soon turn brown.

Host Plants

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Locust leaf miners prefer to mine the leaves of black locust but they have been reported from honey locust and a few other trees as well. Apple, beech, birch, cherry, elm, oak, and hawthorn are occasionally attacked. Outbreaks of this leafminer occur almost every year throughout the range of black locust, but seldom affect the same trees for more than a couple of years. Sometimes the damage is quite noticeable with acres of black locusts turning brown by mid summer. A few years ago we had a minor outbreak here in Raleigh that nobody noticed because black locust is mostly a weed tree here (however, it does make a fine shade tree). If trees are severely defoliated by locust leafminers and other stress factors are present, some trees may even die.

Residential Recommendation

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In a landscape the best time to spray a pesticide is in late May or early June when the adult locust leafminers are active and the larval mines are less than ¼ inch long. An insecticide with some systemic activity such as Orthene or imidacloprid will give the best control.

References

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For assistance with a specific problem, contact your local Cooperative Extension Center.

This Factsheet has not been peer reviewed.

Author

Professor Emeritus
Entomology and Plant Pathology

Publication date: Dec. 18, 2013
Revised: Oct. 1, 2019

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