Elm Leaf Beetle

Elm Leaf Beetle Larvae

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Pest Identification & Damage

Common Name(s): Elm leaf beetle

Scientific Name: Pyrrhalta luteola (Muller), Coleoptera: Family Chrysomelidae.

Identifying Characteristics for Damaging Stage(s):

Adult beetles are black and greenish-yellow, and about 1/4 inch long. The outer edge of each wing cover is bordered with black. The larvae are yellow when first emerged from the egg, then becoming darker as they increase in size. Each has a broad central dorsal stripe of yellow and black to brown striping on each side. The larva causes the greatest amount of feeding damage.

Damage/Nature and Symptoms:

Elm leaves are skeletonized by feeding larvae. Two periods of damage usually occur, the first in June and the second in August/September, coinciding with the appearance of the two generations of larvae. Damaged trees may develop a grayish color as the green leaf tissue is consumed by thousands of voracious yellow and black marked worms. Eventually trees may turn brown as the leaves die and some leaves may drop.

Distribution and Life Cycle

Distribution:

A European insect introduced to the U.S. around 1830, this pest is now found throughout the country. It attacks American, Chinese and Siberian elms. Adult beetles are common household pests when they invade structures in the fall.

Summary of Life Cycle:

Adults (beetles) spend the winter in sheltered places, especially home attics and wall voids. Their presence is noticed during warm periods in winter when they emerge from hibernation and crawl about the house. In the spring the beetles fly to nearby elms and begin to lay their yellow, lemon-shaped eggs in double rowed masses of 25 to 30 each on the undersides of leaves. When eggs hatch, young worms begin to skeletonize leaves, feeding for about 21 days. When they are mature, they crawl down the trunk, where they collect beneath mulch, stones, boards or other items and transform to their pupa stage, which is yellow. After 12 days, they emerge as beetles, mate and fly to the leaves to deposit eggs, which marks the beginning of the second generation. These new worms feed, then crawl down the trunk when mature, to emerge as the second batch of beetles in September, and these insects later seek and enter winter hibernation quarters.

Management Methods:

Inspection/Survey Methods:

Periodically examine elms for the presence of beetles, egg masses and larvae. Critical months are June and July/August.

Non-Chemical Management Strategies:

Carefully seal and screen entry points into homes and other structures to reduce overwintering opportunities. Place small boards, shingles or pieces of coarse fabric at bases of elm trees to attract larvae. Periodically remove these and saturate larvae and pupae with warm, soapy water.

Chemical Management Strategies:

If the attic is used only for storage of non-food items, you can hang No-Pest resin strips in early September to reduce overwintering beetles. If the developing infestation seems to be heavy during the summer, plan to spray trees, otherwise concentrate on reducing populations by treating tree trunks and soil around bases of trees for pupating larvae. Good spray coverage will be essential to prevent extensive leaf damage.

For the latest information on available chemical controls, consult the Pesticide Selection Guide.

References:

Metcalf, C. L., W. P. Flint and R. L. Metcalf, 1962. Destructive and Useful Insects. 4th Ed.: McGraw-Hill Book Co., New York NY. 1087 p.