The adult boxwood leafminer is a tiny 1/10 inch in length,
fragile, orange-yellow, gnat-like fly. The larva or maggot is yellowish-white
about 1/8 inch long. The adult hawthorne leafminer is a sawfly,
a bee-like insect. The larvae have flattened bodies with three pairs
of legs and averages about 2/10 inch in length when fully grown.
adult oak leafminer is a small moth. Larvae are usually
about 1/10 inch long. The adult birch leafminer is
a small, black sawfly about 1/10 inch long. The larva is whitish,
somewhat flattened and slightly over 1/4 inch long when full
grown. It has distinct black spots in the middle of the underside
of the thoracic and first abdominal segments.
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Figure 1. Birch Leafminer Damage
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Figure 2. Leafminer Damage on Honeysuckle
adult holly leafminer is a small black fly introduced
from Europe. The larva is a small yellowish-white maggot about
1/6 inch long.
leafminer. The boxwood leafminer adult emerges in the spring
when weigelia begins to bloom. The adult female begins laying eggs
on the underside of young leaves inserting each egg deep into the
tissues. An average of 29 eggs are laid and she dies hours after
her first eggs are laid. The eggs begin to hatch in about 3 weeks
and the young larvae begin feeding in the soft parenchyma tissue.
Mined or blistered leaves are visible from mid summer until the
following spring.The insect passes the winter as a partly grown
larva in the leaves. In the spring, it become active and grows quickly.
Pupation occurs in late April. There is only one generation per
leafminer. The adult hawthorns leafminer emerges on May when
first leaf clusters begin to unfold and blossom buds begin to open.
Eggs, 1-5 per leaf, are laid singly in the upper epidermis at the
base of the leaf. The larvae feed for about 2 weeks on the parenchyma
between leaf surfaces. They mine toward the distal end, generally
close to the margins. By mid July they abandon the foliage, drop
to the ground and construct earthen cells in preparation for winter.
There is one generation per year.
leafminer. The adult oak leafminer female lays her eggs on the
leaf surface and each young larva bores into the leaf and proceeds
to tunnel in various directions. If mining of the leaf is heavy,
death of the leaf may result. Generally white and red oaks are attacked.
The larvae then pupate inside the leaf and overwinter inside the
dried leaves on the ground. Depending on the location and species,
there may be from 2-5 generations per year.
leafminer. The adult birch leafminer lay eggs singly in new
leaves: Gray, paper, and white birch are favorite hosts. It rarely
feeds on black, yellow, European white or river birch. Larvae feed
between the upper and lower layers of the leaf forming a large hollowed-out
blotch. Larval development is about 10-15 days. When mature, the
larva cuts a hole through the leaf and drops to the ground. A cell
is constructed in which pupation occurs. It takes 2-3 weeks for
transformation into the adult stage. There may be 2-4 generations
leafminer. Adult holly leafminers emerge around May 1 after
a few new leaves have formed. Emergence may continue over several
weeks. Females lay eggs in slits on the underside of the leaves.
Upon hatching, the larvae make slender, narrow mines in the leaves
up to 1/2 inch in length. Later the mines broaden into a long blotch.
After feeding, the larvae pupate and overwinter in the leaf. There
is only one generation per year.
Leafminers cause yellow spotting of the leaves and premature leaf
drop. The plants grow poorly and have sparse foliage. Repeated infestations
can result in dead twigs and a weakened plant, subjecting it to
disease and winter kill in colder areas. The hawthorne leafminer
can be a serious pest of certain species and cultivars of Crataegus
sp. From a distance heavily infested trees will have a brownish
cast as though singed by fire. Injury to the tree is not long lasting,
but can reduce the aesthetic quality and salability of the plant.
The oak leafminer normally does not cause any serious damage
to their hosts. The ornamental value may be reduced if mining is
extensive. The birch leafminer is attracted to vigorously
growing trees and usually these trees are able to withstand several
years of attack. Most problems arise from loss of aesthetic qualities
and salability of plant material. The holly leafminer causes
injury to the tree both in the adult and larval stages. Adults leave
tiny round feeding scars and leaf distortion results from uneven
feeding punctures. With heavy infestations, every leaf can be mined
causing the leaves to drop and leaving the tree practically bare
until the next spring. This can be quite destructive especially
in commercial orchards of "Christmas" holly. In a landscape
setting excessive mining can lead to poor growth and loss of vigor.
Nursery plants may not be salable if heavy infestations are present.
Control of most miners can be achieved by burning the leaves in
the fall which contain overwintering larvae or pupae.
For those species that do not overwinter in the fallen foliage,
chemical insecticides are available and should be applied just as
the eggs are being laid on the foliage.