This sawfly was first recorded in the US (from Europe) in CT in 1923. Adults are black and approximately 0.12 inches in length. Egg-laying female sawflies are attracted to fast growing, tender, spring foliage. Eggs are laid in these leaves singly. Once they hatch, larvae mine within the leaf. Larvae are flat. Young mines are small and individualized, but as larvae grow, the mines converge and become a large, hollowed-out blotch. A full grown larva can be 0.24 inches long. Once mature, the larva will chew its way out of the leaf and drop to the ground to pupate. Two-four generations are possible per year, depending on local temperatures. Subsequent generations of the birch leafminer in the same season may reinfest the leaves again if the host refoliates in the same year.
Foliage of native white-barked birches are primarily impacted. Damage may be first apparent as dark greenish spots on the leaves. Young larvae create small, individual mines between the upper and lower surfaces of tender, new leaves. As the larvae grow, the mines converge and become one large, brown, hollow blotch. Larvae may be visible within these blotches if the leaf is held up to the light. Healthy trees can withstand several years of attack before showing signs of decline.
Monitor adults with yellow sticky cards to time sprays. First generation adults lay eggs when new leaves are about half emerged. It is most important to monitor for and manage the first generation of this insect each year.
When possible, plant resistant birches. Betula alleghaniensis, Betula grossa, and Betula lenta are thought to be highly resistant to the birch leafminer. Betula dahurica, Betula maximowicziana, Betula platyphylla, Betula schmidtii, and Betula costata show partial to intermediate levels of resistance to birch leafminer (Davidson and Raupp, 2014).
Native parasitoids in North America do attack the birch leafminer, however historically did not keep populations below damaging levels. Exotic biological control agents have been established, including Lathrolestes nigricollis and Grypocentrus albipes (ichneumonid wasps) and one eulophid wasp (Chrysocharis nitetis), which have been reported to have reduced birch leafminer to barely detectable levels in areas of MA, CT, RI, NY, and PA.
Lathrolestes nigricollis has become established and widely distributed (Van Driesche et al., 1997). Grypocentrus albipes, while established in a few locations, has been recovered much less frequently by researchers. L. nigricollis has resulted in decreases from 50 to less than 5% of first generation leaves being mined by the birch leafminer (Van Driesche et al., 1997).
Abamectin (NL)
Acephate (NL)
Acetamiprid (L)
Azadirachtin (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorantraniliprole (NL)
Clothianidin (NL)
Cyantraniliprole (NL)
Cyfluthrin (NL)
Deltamethrin (L)
Diflubenzuron (N)
Dinotefuran (NL)
Emamectin benzoate (L)
Fenpropathrin (NL)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Imidacloprid (L)
Insecticidal soap (NL)
Lambda-cyhalothrin (L)
Malathion (L)
Neem oil (NL)
Permethrin (L)
Pyrethrin+sulfur (NL)
Spinetoram+sulfoxaflor (N)
Spinosad (NL)
Chemical management may no longer be needed due to the successful biological control efforts for this insect. Manage adults prior to egg laying. Soil and trunk injection with imidacloprid, where applicable, has shown good results.
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirchtin (injection, soil drench), chlorantraniliprole (soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), diflubenzuron (soil drench), dinotefuran (soil drench), emamectin benzoate (injection), imidacloprid (soil drench), and neem oil (soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022 neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.