Birch leafminer
Encyclopedia
Birch leafminers are sawflies
, which are closely related to bees and wasps. They are among the most common insect pests affecting Birch
trees (Betula spp.) in North America. Areas inside the leaves are consumed by the larva
e affecting the leaves' ability to produce food. Yearly browning of birch leaves are noticed in mid July and August, but the leafminers have been feeding inside the leaf tissue since early spring.
(egg-laying) peaks during the last week of June. Adult birch leafminers are small (about 1/8 to 1/4 inch long), black and fly like. Females deposit their eggs singly in slits cut in the central areas of young leaves, usually near the tips of branches. More than one female may lay eggs in a leaf.
The eggs hatch into legless, worm-like larvae. These immature larvae feed individually between the leaf surfaces, creating blotchy kidney shaped mines. The immature leafminers feed for several weeks, then drop to the ground where they enter the soil layer to develop into pupa
e. They pupate and remain there until the following spring. After overwintering as prepupae in the soil below the tree, the adults emerge just as the birch trees are leafed out. Adults are almost all females.
area of the leaf. Heavy infestations of leafminer larvae can seriously affect a tree's photosynthetic capacity. Repeated attacks will generally cause stress which may induce susceptibility of the tree to other injurious agents.
area have been successfully controlled with releases of a parasitic wasp, Lathrolestes luteolator. Populations of the tiny parasitoid
wasp selectively attack the most damaging birch leafmining pest (Profenusa thomsoni) have developed and drastically reduced the problem in the Edmonton area of Canada.
Following trials in 1995 that supported a dramatic reduction in birch leafminer damage by the first parasitoid, the City of Edmonton, Canada discontinued pesticide treatments to almost 3,500 city birch trees in 1996 and 1997. These trees continue to show very little leafminer damage without any treatment.
can be used to control birch leafminers prior to extensive damage. Spinosad is a new chemical class of insecticide
s derived from a soil dwelling bacterium discovered in 1982. It is considered practically non-toxic to humans, pets, and beneficial insects. Unlike other insecticides, Spinosad will not harm beneficial insects including the Amber Marked Leafminer parasite.
Horticultural oil applications applied at the right time may help kill eggs or tiny larvae within the leaf tissue. Oil applications should be made as soon as adults have emerged in the spring and egg laying has occurred and should continue weekly until mid June. Pesticides made with botanical plant oils may be especially useful to prevent egg laying. Neem
oil acts as a repellent and may interfere with the egg laying activity of female leaf miners.
Systemic insecticides are chemical pesticides that are absorbed into the tissues of plants. These pesticides make the entire plant, or parts of the plant, poisonous to insects that feed on the plant tissue. Most systemics are very toxic to people and pets. Trunk injections are confined to the tree's cambium
layer, where it is carried to the leaf tissue by the movement of the tree's sap.
Urban Forestry, City of Edmonton, Alberta Canada.
Parkland Services Urban Insect and Disease Report. Ed Holsten, Research Entomologist USDA Forest Service: Alaska Region; S&PF, FHP & PNW, personal communication.
USDA Forest Service, Amber Marked Birch Leafminer Leaflet R10-TP-114 April 2003.
Sawfly
Sawfly is the common name for insects belonging to suborder Symphyta of the order Hymenoptera. Sawflies are distinguishable from most other Hymenoptera by the broad connection between the abdomen and the thorax, and by their caterpillar-like larvae...
, which are closely related to bees and wasps. They are among the most common insect pests affecting Birch
Birch
Birch is a tree or shrub of the genus Betula , in the family Betulaceae, closely related to the beech/oak family, Fagaceae. The Betula genus contains 30–60 known taxa...
trees (Betula spp.) in North America. Areas inside the leaves are consumed by the larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e affecting the leaves' ability to produce food. Yearly browning of birch leaves are noticed in mid July and August, but the leafminers have been feeding inside the leaf tissue since early spring.
Life cycle
Leafminers overwinter in the soil as prepupae. Adults emerge in May to late June to early July, depending on temperature and humidity. OvipositionOviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
(egg-laying) peaks during the last week of June. Adult birch leafminers are small (about 1/8 to 1/4 inch long), black and fly like. Females deposit their eggs singly in slits cut in the central areas of young leaves, usually near the tips of branches. More than one female may lay eggs in a leaf.
The eggs hatch into legless, worm-like larvae. These immature larvae feed individually between the leaf surfaces, creating blotchy kidney shaped mines. The immature leafminers feed for several weeks, then drop to the ground where they enter the soil layer to develop into pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
e. They pupate and remain there until the following spring. After overwintering as prepupae in the soil below the tree, the adults emerge just as the birch trees are leafed out. Adults are almost all females.
Damage
The areas of leaves that are consumed by the amber marked birch leafminer larva turn brown. Because people often do not see the early signs of birch leafminer feeding, it often appears the tree has suddenly dried up or become diseased. This browning is caused by the outer layers of the leaf drying out after the leaf miner larva has consumed the green tissue between the outer layers of the leaf. Early mines appear as light green or whitish discolorations on the leaves. Larvae sometimes can be seen easily when leaves are held up to sunlight, especially as the mines and larvae grow larger. Feeding over several weeks causes the blemish to take on a blister-like appearance. A single leaf can contain as many as 40 larvae whose mines may merge to destroy the total photosyntheticPhotosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
area of the leaf. Heavy infestations of leafminer larvae can seriously affect a tree's photosynthetic capacity. Repeated attacks will generally cause stress which may induce susceptibility of the tree to other injurious agents.
Species Responsible
There are two species mainly responsible for defoliation and browning of birch trees in the United States and Canada. In Northern forests, it is the Amber Marked Leafminer, Profenusa thomsoni, which were accidentally introduced from Europe to North America early in this century. The other is the Birch Leafminer, Fenusa pusilla, which is more common in Eastern forests.Biological Control of Birch leafminers
Presently there is no commercially available biological control agent to control Amber marked birch leafminers, however Canadian trees in the EdmontonEdmonton
Edmonton is the capital of the Canadian province of Alberta and is the province's second-largest city. Edmonton is located on the North Saskatchewan River and is the centre of the Edmonton Capital Region, which is surrounded by the central region of the province.The city and its census...
area have been successfully controlled with releases of a parasitic wasp, Lathrolestes luteolator. Populations of the tiny parasitoid
Parasitoid
A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...
wasp selectively attack the most damaging birch leafmining pest (Profenusa thomsoni) have developed and drastically reduced the problem in the Edmonton area of Canada.
Following trials in 1995 that supported a dramatic reduction in birch leafminer damage by the first parasitoid, the City of Edmonton, Canada discontinued pesticide treatments to almost 3,500 city birch trees in 1996 and 1997. These trees continue to show very little leafminer damage without any treatment.
Chemical Control
SpinosadSpinosad
Spinosad is a new chemical class of insecticides that are registered by the United States Environmental Protection Agency to control a variety of insects...
can be used to control birch leafminers prior to extensive damage. Spinosad is a new chemical class of insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
s derived from a soil dwelling bacterium discovered in 1982. It is considered practically non-toxic to humans, pets, and beneficial insects. Unlike other insecticides, Spinosad will not harm beneficial insects including the Amber Marked Leafminer parasite.
Horticultural oil applications applied at the right time may help kill eggs or tiny larvae within the leaf tissue. Oil applications should be made as soon as adults have emerged in the spring and egg laying has occurred and should continue weekly until mid June. Pesticides made with botanical plant oils may be especially useful to prevent egg laying. Neem
Neem
Azadirachta indica is a tree in the mahogany family Meliaceae. It is one of two species in the genus Azadirachta, and is native to India growing in tropical and semi-tropical regions. Its fruits and seeds are the source of neem oil...
oil acts as a repellent and may interfere with the egg laying activity of female leaf miners.
Systemic insecticides are chemical pesticides that are absorbed into the tissues of plants. These pesticides make the entire plant, or parts of the plant, poisonous to insects that feed on the plant tissue. Most systemics are very toxic to people and pets. Trunk injections are confined to the tree's cambium
Cambium (botany)
A cambium , in botany, is a tissue layer that provide undifferentiated cells for plant growth. It forms parallel rows of cells, which result in secondary tissues....
layer, where it is carried to the leaf tissue by the movement of the tree's sap.
Sources
Natural Resources Forestry Canada, Northern Forestry Centre. Edmonton, Alberta. For. Leafl. 5.Urban Forestry, City of Edmonton, Alberta Canada.
Parkland Services Urban Insect and Disease Report. Ed Holsten, Research Entomologist USDA Forest Service: Alaska Region; S&PF, FHP & PNW, personal communication.
USDA Forest Service, Amber Marked Birch Leafminer Leaflet R10-TP-114 April 2003.