Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
Elm Leaf Beetle
Elm
leaf beetles are plant feeders both in the adult and larval stage. They feed
almost exclusively on elm trees, and the most damage is done by the larva,
which skeletonizes the elm leaves. Elm leaf beetles
occasionally become annoying in the home. Adult beetles enter structures during
the autumn but may be most troublesome during the spring when they become
active after hibernation in attempting to get back outside to elm trees.
Although these beetles do not harm humans or their possessions, they are
sometimes confused with carpet beetles and other household pests and considered
a nuisance by their presence.
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Identification Adult elm leaf beetles are about 1/4 inch long,
1/8 inch wide and elongate oval in shape. Beetles vary from yellow
when young to olive green when mature, with a black stripe along the outer
edge of the wing covers. There are four black spots on the thorax. During the
winter, many beetles fade in color and by spring appear dull to olive green
with the edge stripes less distinct. Eyes are black and the antennae and legs
are yellowish. Larvae are about 1/2 inch long and dull yellow with two dark
stripes down the back. Pupae are about 1/4 inch long and bright
yellowish-orange. Eggs are about 1/16 inch long, yellowish to orange,
spindle-shaped and attached in clusters of 5 to 25 in two or three parallel
rows on the undersides of elm leaves. |
Elm Leaf Beetle |
Life Cycle and Habits
Elm
leaf beetles over winter as adults in homes, buildings, wood piles, tree bark
crevices, debris at the tree base and other protected places. During the
spring, beetles leave their over wintering quarters, become active and fly to
elms (especially Chinese or Siberian elm) and American elm, and begin feeding
on newly emerged leaves. Egg-laying begins in late May and early June, with
each female laying between 400 and 800 eggs over her life span. Eggs hatch in
about seven days. Small, black larvae feed on the leaves and mature in two to
three weeks. Young larvae feed in groups and older larvae sometimes singly.
Pupation occurs in tree bark crevices or on the ground in sheltered places,
with new adults emerging about 10 days later. There are two or more generations
per year depending on the season. Both adults and larvae feed on the elm
foliage. Adults chew small, round, irregular holes in the leaf, whereas the
larvae skeletonize, leaving only the vein intact. When
damage is severe, leaves curl, dry out and fall prematurely.
Foliage
feeding usually will not kill the tree but may weaken it, resulting in more
susceptibility to branch dieback, attacks of bark beetles and borers, as well
as disease organisms such as Dutch elm disease. However, elm bark beetles, not
elm leaf beetles, transmit this serious fungus disease of American elm.
Control
Measures
Natural
There
are/several natural enemies of elm leaf beetles such as birds, toads, diseases,
and predaceous and parasitic insects. A chalcid wasp
frequently kills many pupae. The fungus Beauveria
bassiana (Bals.) also
kills pupae and even adults during late summer, especially in humid seasons.
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Indoors Beetles
in the home can be collected with a vacuum cleaner or broom and dustpan for
disposal. Household pressurized aerosol sprays of pyrethrins
applied directly on the beetles are effective. Collect dead and dying beetles
soon after for disposal. Prevent
entry at window wells, doorways, unused fireplaces, etc. by providing
tight-fitting screens and snug windows and doors. Stuff cotton in sash cord
channels and use caulking compound to repair cracks and cervices in the house
foundation, around doors and windows and other possible entry points. Crack
and crevice treatments of amorphous silica gel (Tri-Die) or boric acid (Perma-Dust) will help. |
Larvae on elm
leaf |
Outdoors
For
control of beetles crawling on and into buildings, spray the exterior
foundation, outside walls of the house, around window wells, doorways, etc.
On
Trees
Thorough
spray coverage of all foliage is essential. Use appropriate spray equipment of
sufficient capacity, especially for tall trees. (Commercial spraying may be
needed for a community-wide control program).
Apply
in early spring when eggs are hatching, new larvae are appearing and leaf skeletonizing is first observed on fully expanded leaves
usually in late May. A second spray may be needed in July for second generation
larvae. Carefully inspect the undersides of the leave for small, black larvae
and spray only if found in large numbers with leaf skeletonization.
Only the trunk of the tree needs to be sprayed when larvae are near the tree
base and prior to pupation.
Information obtained through the Ohio State Extension
FactsheetHYG-2036-94
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES