Forest & Grassland Health

Birch Leafminers

Amber-marked birch leafminer (Profenusa thomsoni [Konow])
Late birch leaf edgeminer (Heterarthrus namoratus Fallen)
Also present is birch leafminer (Fenusa pumila Leach), not currently an issue in Alaska, so it is not discussed.

Host(s) in Alaska:

All native species of birch in Alaska (Betula spp.); Alaska paper birch, dwarf arctic birch, Kenai birch, paper birch, resin birch, western paper birch
Alder (Alnus spp.)

Habitat(s): Birch leaves (development) and in the duff/leaf litter (overwintering)

Photos

Click on the image for a larger version.

AMBLM ovipositing on a leaf

Amber-marked birch leafminer ovipositing on a leaf.

 

AMBLM adult roughly 4-5 mm in length

Amber-marked birch leafminer adult roughly 4-5 mm in length.

Distinguishing between mines constructed by AMBLM (yellow-brown mines fill with frass) and LBLE (red

Mines of amber-marked birch leafminer (yellow-brown with frass) and late birch leaf edgeminer (reddish without frass).

AMBLM mines in Fairbanks birch

Amber-marked birch leafminer mines in a birch leaf in Fairbanks.

During outbreaks invasive birch leaf miners can impact >90% of a trees leaves

During outbreaks invasive birch leafminers can impact >90% of a tree's leaves

Current Status & Distribution in Alaska (2019 Update)

In 2019, special late-season aerial surveys were scheduled in both Southcentral and Interior Alaska to better assess the impacts of these invasive insects; in 2018, August aerial surveys had detected birch leafminers farther from major population centers and roadways than ever before. Over 280,000 acres of impacted forests were mapped in 2019. In the Interior 17,000 acres of damage were recorded with > 9,000 acres observed between Fairbanks and Eielson Air Force Base. In Southcentral, over 170,000 acres of birch leafminer damage were recorded in the Matanuska-Susitna Borough and over 80,000 acres were mapped on the northern Kenai Peninsula. Additionally, a small area of activity was noted on the west side of Cook Inlet in the Big River Lakes area, 45 miles west of the nearest known birch leafminer infestation on the Kenai Peninsula. Based on the extent of the damage in this area and its geographic isolation from other known infestations, it appears to be a more recent introduction. It is unknown how these leafminers were introduced, but the area is a popular recreation site. Prior to 2018, invasive birch leafminers were believed to predominantly infest stands in major population centers and along roadways. Survey flights in Auguts 2018 in the Matanuska-Susitna Valley detected birch leafminer activity extending to remote forests, prompting additional later surveys in 2019. Based on ground surveys, all birch leafminer damage mapped in 2019 was presumed to be either amber-marked birch leafminer (P. thomsoni) or late birch leaf edgeminer (H. nemoratus). Damage in the Interior was predominately from amber-marked birch leafminer, whereas most damage in Southcentral was from the late birch leaf edgeminer; the incidence of both species was similar on the Kenai Peninsula. Little birch leafminer damage was observed in Southeast Alaska in 2019, possibly due to abnormally dry conditions. 

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Historic Activity

Invasive birch leafmining sawflies are believed to have entered eastern North America in the early 20th century, dispersed across Canada, and entered Alaska in the early 1990s. Birch leaf miner damage, specifically amber-marked birch leafminer (P. thomsoni), was first reported in Haines in 1991, but was not properly identified until it was detected in Anchorage in 1996. Following its introduction to Anchorage, sawfly populations increased dramatically, growing to outbreak levels throughout the Anchorage Bowl, and to a lesser degree the Mat-Su Valley and Kenai Peninsula. Damage caused by the amber-marked birch leafminer peaked in 2006 followed by a steady reduction in activity. During this period, the initially dominant amber-marked birch leafminer was displaced by late birch leaf edge miner, which reached peak severities affecting roughly 50% of leaves on infested birch in 2012.

In 2002, amber-marked birch leafminer was detected in Fairbanks where populations have intensified over the past 15 years. An initial absence of amber-marked birch leafminer populations between Fairbanks and Anchorage, and scattered occurrences along roadways and on pullouts, suggests an anthropogenic aided dispersal.

In response to rising leaf miner populations and their corresponding damage to birch leaves, biological control efforts were implemented from 2004 to 2008. During this period, more than 3,000 Lathrolestes thomsoni Konow (Hymenoptera: Ichneumonidae), a parasitoid linked to the collapse of leaf mining populations in Canada and the eastern U.S., were released in multiple locations, primarily in the Anchorage area. Following parasitoid release, percent of birch leaves mined dropped by 30-40%, but a similar decline in leaf miner activity observed in non-release sites made the impacts of Lathrolestes difficult to determine. However, since its release Lathrolestes has successfully become established in Alaska and is spreading out from release sites parasitizing invasive leaf miners in new locations. Additionally, while monitoring for the released parasitoid, two naturally occurring parasitoids, L. soperi Reshchikov and Aptesis segnis Provancher (Hymenoptera: Ichneumonidae), were discovered attacking birch leaf miners. While the exact impacts of parasitoids preying on leaf miner populations is not yet known, it is hoped they will help reduce pest populations in the future.

In road surveys in 2017 and 2018, we found that both P. thompsoni and H. nemoratus have expanded their ranges in Interior Alaska. In Fairbanks, P. thomsoni is still heavily impacting birch trees, and in 2018 was found for the first time in Delta Junction and nearby Clearwater State Recreational Area. Locations with H. nemoratus present in Fairbanks more than doubled from 2017 to 2018 (5 to 11 sites). H. nemoratus was recorded at several locations along a 30-mile stretch of the Parks Hwy north of Healy, and was found for the first time at the Delta Junction visitor center.

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Biology, Symptoms, Impacts, Population Dynamics

Biology: Invasive birch leaf miners in Alaska are Palearctic sawflies (Hymenoptera: Tenthredinidae) a primitive species of stingless wasp.  Amber-marked birch leaf miner overwinter in soil cocoons, pupate in summer, and emerge in late June early July. All adults are females and reproduce via parthenogenesis (i.e. no males, viable eggs are oviposited without the need for fertilization). Eggs are oviposited in slits cut into the midsection of birch leaves, and hatch within 12 days. Larvae feed between a leaf’s epidermal layers, “mining” the leaf, and develop through six stages (instars) over a period of 24 days. Only the first five instars are feeding; when the larval stages nears completion, larvae emerge from leaves, drop to the soil, and construct cocoons for overwintering.

Late birch leaf edge miner is very similar in life cycle and biology to amber-marked birch leafminer, but there are notable differences. Female late birch leaf edge miners oviposit eggs on outer edges of leaves, and this is where the mines occur (thus the name “edge miner”). Mines of late birch leaf edge miner take on a reddish hue distinguishing them from the yellowish-brown mines of amber-marked birch leafminer. Late birch leaf edge miner larvae make small slits in leaves to eject frass (insect feces) and shed larval skin from their mines; this behavior appears to be unique for this species among birch mining sawflies. Lastly, late birch leaf edge miner larvae pupate in the fall; pupae remain in leaves during leaf drop and overwinter in cocoons within their leaves on the ground. Both amber-marked birch leafminer and late birch leaf edge miner have a single generation per year (univoltine).

Symptoms: Amber-marked birch leafminer larval feeding becomes obvious in late July early August after a substantial portion of the leaf has been mined.  Browning foliage can be mistaken for early senescence (i.e. transition to fall colors), but close examination of the leaf will prove otherwise: 1) Mined leaves will appear a sickly yellowish-brown compared to the vibrant gold naturally exhibited by birch in autumn, 2) leaf epidermal layers will have become detached due to larval feeding, and the leaf will take on the appearance of a flattened or collapsed blister filled with frass (insect feces), and 3) if the leaf is examined prior to larval emergence, the flattened yellowish larvae (6 mm in length) can be observed within affected leaves.

Both amber-marked birch leafminer and late birch leaf edge miner can be found in the same tree or even in the same leaf, but the mines caused by these species are distinguishable. Late birch leaf edgeminer mines are a reddish ring on the edge of a leaf, expanding inward, and contain little frass. In contrast, amber-marked birch leafminer mines begin in the center of the leaf, often near a major lateral vein, and expands outward, and contain notable dark frass. Regardless of the species, impacts to birch trees from the two species appear to be similar.

Impacts: Negative impacts from invasive birch leafmining sawflies in Alaska are primarily aesthetic. During outbreaks >90% of a tree’s leaves can be infested by sawflies. Mining disrupts a tree’s ability to conduct photosynthesis, but the majority of damage occurs later in the summer after most tree growth has occurred. Alaska’s long summer daylight hours in May, June, and July may provide enough photosynthetic potential for trees to flourish despite a reduced capacity for photosynthetic at the end of the season. To date, we have not recorded birch mortality due to these insects. We will continue to monitor birch mining sawfly populations and their birch hosts in the years ahead to determine possible long-term impacts from these invasive pests.

Population Dynamics: A major variable in reductions of amber-marked birch leafminer populations may be found in the sawfly’s egg laying behavior. Amber-marked birch leaf miner preferentially lay eggs on leaves that already have amber-marked birch leafminer eggs. Therefore, when amber-marked birch leafminer population levels are elevated, egg densities per leaf may become too high to sustain the hatched larvae. With insufficient resources available, many larvae never complete development. As the number of eggs per leaf approaches ten, mortality of larvae on the leaf approaches 100%.

The wasp Lathrolestes thomsoni (Hymenoptera: Ichneumonidae) (no common name) is a known parasitoid of birch leafminers in North America. Parasitoids lay their eggs in or on host organisms. Upon hatching, parasitoids consume and kill their hosts. Lathrolestes thomsoni inject eggs into sawfly larvae, sawfly larvae complete development, build overwintering cocoons, and pupate as normal, but it is the parasitoid not the sawfly that emerges from the cocoon the following spring. Reductions in amber-marked birch leafminer populations in Alberta, Canada and the eastern U.S. have been associated with L. thomsoni, and this parasitoid has successfully become established in Alaska. The effects of parasitoids on birch leaf-mining sawfly populations in Alaska has yet to be determined.

Competition between the amber-marked birch leafminer and late birch leaf edge miner has the potential to negatively impact both populations. Research from outside Alaska suggests that there may be niche partitioning between amber-marked birch leafminer and late birch leaf edge miner, with amber-marked birch leafminer preferring leaves in the lower canopy and late birch leaf edge miner preferring the upper canopy. However, observations in Alaska have reported both species readily attack leaves throughout the canopy, and are often found in the same leaf.

The cause of the apparent collapse of amber-marked birch leafminer populations in many locations in Southcentral Alaska requires further investigation. Was it due to a detrimentally high density of eggs per leaf, the establishment of parasitoids, competition between two species, a combination or all of the above, or a factor not yet determined? Will a similar collapse in populations in the Interior and Southcentral be observed where population densities are still high? Continued monitoring of amber-marked birch leafminer and late birch leaf edge miner populations will help us to answer these questions.

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Survey Method

Symptoms become apparent late-summer in 2018 following aerial detection surveys; therefore, damage extent and severity is monitored through ground-survey.  Damage assessments of birch leafminer activity were based on percent of impacted leaves: Not Present 0%, Present 1-5%, Low 6-30%, Moderate 31-60%, High >60% (see distribution maps below). 

Birch leafminer damage can be mapped during aerial surveys. Prior to 2018, invasive birch leaf-mining sawflies were thought to predominantly impact areas within major population centers and along roadways. Aerial surveys in Southcentral Alaska were conducted later in 2018, and damage was observed extending to remote forests. 

 

Detection Maps (2019)

Birch leafminers detected in aerial and ground surveys in 2019.

Birch leafminer activity detected in aerial and ground surveys in 2019.

Links to Resources & Publications

Digweed, S., R. McQueen, J. Spence, and D. Langor. 2003. Biological control of the ambermarked birch leafminer, Profenusa thomsoni (Hymenoptera: Tenthredinidae). Alberta.Information Report NOR-X-389, Northern Forestry Centre, Canadian Forest Service, Natural Resources Canada, Edmonton, Alberta.

Digweed, S. C., C. J. MacQuarrie, D. W. Langor, D. J. Williams, J. R. Spence, K. L. Nystrom, and L. Morneau. 2009. Current status of invasive alien birch-leafmining sawflies (Hymenoptera: Tenthredinidae) in Canada, with keys to species. The Canadian Entomologist 141:201-235.

Goulet, H. 1992. Insects and arachnids of Canada part 20. The genera and subgenera of the sawflies of Canada and Alaska. Hymenoptera: Symphyta.

MacQuarrie, C. J. K. 2008. Invasion history, population dynamics and biological control of Profenusa thomsoni (Konow) in Alaska. ProQuest.

Martin, J. L. 1960. The Bionomics of Profenusa thomsoni (Konow)(Hymenoptera: Tenthredinidae) a leaf-mining sawfly on Betula.. The Canadian Entomologist 92:376-384.

Snyder, C., C. J. MacQuarrie, K. Zogas, J. J. Kruse, and J. Hard. 2007. Invasive species in the last frontier: distribution and phenology of birch leaf mining sawflies in Alaska. J. For. 105:113-155.

Soper, A. L., C. J. MacQuarrie, and R. Van Driesche. 2015. Introduction, establishment, and impact of Lathrolestes thomsoni (Hymenoptera: Ichneumonidae) for biological control of the ambermarked birch leafminer, Profenusa thomsoni (Hymenoptera: Tenthredinidae), in Alaska. Biological Control 83:13-19.

 

Content prepared by: Stephen Burr PhD, Forest Entomologist, USDA Forest Service stephen.burr@usda.gov (now working in USFS Region 9).
 

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