The smaller European elm bark beetle was first reported in the United
States in 1909. Its presence in this country was given significance with
the introduction of the Dutch elm disease in 1930. The beetle attacks
all native and introduced species of elms and now occurs wherever the
hosts are present. The feeding of the adult beetles in the spring is
responsible for transmitting the Dutch elm disease from diseased to
healthy trees. The Dutch elm disease is now our most important shade
tree disease.
[Illustration: Smaller European elm bark beetle adult.]
Adult bark beetles emerge in the spring from dead or dying elms and
begin feeding on the twigs of healthy elms. The female then excavates an
egg gallery in the bark of dead or weakened elms. Eggs are deposited
along the walls of the gallery. The larvae, upon hatching, burrow into
the bark at right angles to the egg gallery. Pupation occurs at the end
of the larval tunnel. New adults tunnel to the bark surface and leave
the tree through circular emergence holes. There are usually two
generations a year. The beetles overwinter in the larval stage.
Chemical control and good tree maintenance are the two methods used to
reduce bark beetle populations. Insecticides are used to prevent feeding
by the adults in the spring. Tree sanitation involves removal and
disposal of dead elms and elm limbs which eliminate breeding and larval
development sites.