Aspen Leafminer

Phyllocnistis populiella Chambers

Host(s) in Alaska:

trembling or quaking aspen (Populus tremuloides)
balsam poplar (P. balsamifera)
black cottonwood (P. trichocarpa)
Occasional: willow (Salix spp.) and ornamental cherry trees (Prunus spp.)

Damage(s): Larvae feed on host leaves

Current Status in Alaska (2023 Update)

Defoliation caused by aspen leafminer was mapped across 80,600 acres in Interior Alaska, up from 38,000 acres of defoliation recorded in 2022. Over 55,600 acres of defoliation were observed within and around the Tanana Valley State Forest from Tanana to Tok. Approximately 20,200 acres of defoliation were observed along the Parks Highway and Nenana Ridge corridor between Fairbanks and Nenana, an area that has traditionally suffered extensive damage from aspen leafminer. Scattered damage was mapped near Manley Hot Springs and Minto. 

Aspen leafminer was observed along every roadway in the Interior, from Fairbanks to just south of the Brooks Range, northeast towards Circle, along both the Alaska and Taylor Highways toward the Canadian border, and south along the Parks Highway to the Alaska Range. Aspen leafminer damage was extensive in the greater Fairbanks North Star Borough area; within two weeks of Fairbanks’ “green up,” aspen stands in Bonanza Creek Experimental Forest and at various sites along the Parks Highway south of Fairbanks were observed as very heavily defoliated. Throughout the field season, trace amounts of aspen leafminer were recorded along the Richardson Highway, but damage was not observable from the road and without close inspection. There were 44 research grade observations of aspen leafminer recorded on iNaturalist in Interior Alaska, mostly concentrated around the greater Fairbanks area.  

Historic Activity

Aspen leafminer is a native moth found across the ranges of its hosts. The first recorded outbreak in Alaska occurred in the late 1970s. More recently, damage in Alaska due to aspen leafminer has predominately occurred among Interior aspen stands. A multiyear outbreak, beginning in 2002, is currently ongoing in Alaska. Acres of infested aspen identified during annual aerial surveys have ranged from over 700,000 acres in 2007 to as low as 69,000 acres in 2012 (see Forest Health Conditions reports 2002-2017 here). The current outbreak is the second recorded outbreak in Alaska exceeding 500,000 acres, the first occurred during the late-1970s.

In 2020, Aspen leafminer was recorded on quaking aspen and balsam poplar during ground surveys along the entire road system north of the Alaska range and south into the Copper River Valley. Damage was also recorded south along the Parks Highway into the Matanuska-Susitna Valley. Aspen leafminer damage was recorded across all size classes of quaking aspen from seedling to poletimber (up to 10” in diameter) and with a fairly even spread across areas surveyed. Trace to heavy damage was also spread across much of the surveyed area, though only trace and light levels were seen on the Richardson Highway south of Glennallen. Stems affected in all areas ranged from a few trees to greater than 30. Leafminer damage was recorded at trace to light levels on balsam poplar seedlings, although it was also quite evident on some saplings. Similar damage has been observed on black cottonwood in Southcentral and Southeast; however, there has been some uncertainty over the taxonomic identity of the damage agent and further investigation is planned. In 2021, Aspen leafminer defoliation was mapped on over 38,000 acres in Interior Alaska, a notable decrease from the 146,000 acres mapped in 2021; over 22,000 acres of defoliation were observed within and around the Tanana Valley State Forest from Tanana to Tok; almost 12,000 acres of defoliation were observed along the Parks Highway and Nenana Ridge corridor between Fairbanks and Nenana, an area that has traditionally suffered extensive damage from aspen leafminer. 

During the 2020 scan and sketch survey almost 39,000 acres of moderate to heavy aspen leafminer damage was recorded. This is a fraction of the acres normally mapped; however, only 2.4 million acres were surveyed in this manner, accounting for one tenth the number of acres regularly surveyed. Almost all  the damage was mapped in the Interior and north of the Alaska Range, with less than 50 acres mapped in Southcentral near Kenai and Soldotna. The amount and extent of the damage across the Interior was not a surprise since it was observed in all areas where it has historically occurred with one exception; there was a lack of damage in the Copper River Valley, from about Paxson Lake south to the Tiekel River. Aspen leafminer is typically very common along the entire road system in the Copper River Valley, and it is not unusual to have moderate to heavy activity throughout the area. Some damage was mapped using scan and sketch survey in the area of Copper Center, but very little was found during ground surveys. The apparent collapse of aspen leafminer populations in this area was unexpected. 

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Biology, Symptoms & Impacts

Biology: Adult aspen leafminers (ALM) are small, white moths with subtle brown or blackish markings on their wings. Aspen leafminers overwinter in the adult stage, employing a freeze avoidance strategy through supercooling and site selection. Supercooling is the physiological process of lowering the body’s freezing point so crystallization occurs at temperatures below 32°F. If they freeze they will die, but supercooled ALM will remain unfrozen at temperatures as low as -25°F. Aspen leafminer preferentially select leaf litter beneath non-host spruce as overwintering sites. Snow cover beneath aspen is deeper, due to a lack of winter foliage, and warmer, due to superior insulation, but leaf litter beneath spruce is drier. Drier locations reduce the risk of “inoculative freezing”, or freezing due to inadvertent contact with ice. Ice can freeze a supercooled aspen leaf miner when crystals in the ice trigger crystallization in the moth, killing moths at temperatures above their supercooling threshold.

Adults emerge in early spring generally just prior to aspen bud break (early May). Following mating, individual eggs are deposited on the edges of newly emerging aspen leaves. Adults then fold leaf edges to form a protective shelter for eggs until larvae hatch (mid to late may). When populations are low, one or two eggs are oviposited per leaf, but up to seven eggs per leaf have been found during elevated population levels such as the current outbreak. When new larvae hatch, they bore into leaves and feed on epidermal tissues. Larvae develop through four instars (developmental stages), are small, white, flat, and reach roughly 5 mm in length. Pupation occurs within mines. New adults emerge slightly before or during leaf senescence (transition to fall colors) in late August and September. There is one generation per year (univoltine).

Symptoms & Impacts: Adults feed on nectar collected from extrafloral nectaries (gland-like swellings) located on the top and at the base of some aspen leaves. The proportion of aspen leaves with extrafloral nectaries can vary greatly (33 to 78% of leaves). Aspen leafminer damage is caused by larval feeding or “mining” of the epidermal tissue on the top or bottom of host leaves. Contrary to earlier belief, they do not feed on the photosynthetic tissues of the mesophyll. Larvae of ALM construct serpentine mines. Mines give aspen leaves a silvery appearance, making them easy to detect during aerial and ground surveys. Balsam poplar and black cottonwood leaves do not take on a silvery appearance, and can be difficult to identify from the air. The majority of damage due to feeding is done by late instar larvae and occurs over a two week period (early to mid-June). Feeding eventually causes leaves to desiccate, turn brown, and drop prematurely.

Aspen leafminer larval feeding disrupts aspen’s ability to conduct photosynthesis and regulate water loss. Mines on the underside of leaves negatively impact photosynthetic rates due to the destruction of guard cells surrounding leaf stomates (leaf pores). Aspen stomata are located on the underside of leaves, and they open and close when surrounding guard cells expand or contract. Stomates allow aspen trees to regulate water loss and photosynthesis. Opened stomates allow for the uptake of carbon dioxide (CO₂), a necessary component of photosynthesis, but water is lost through the openings. Closed stomates reduces water loss but reduces photosynthetic potential, resulting in less “food” for the tree. Reduced photosynthetic rates due to feeding results in reductions in aspen growth rates. Mines disrupt aspen’s ability to regulate water loss. Damage caused by larval feeding allows water to escape to the surrounding air, and limits a tree’s ability to regulate water loss. Environmental conditions, such as drought and/or warming temperature can trigger aspen to open or close stomates depending on whether photosynthesis or water retention has higher priority. Reductions in photosynthesis combined with and an inability to regulate water loss may hinder aspen’s ability to respond to changes in its environment. The long-term impacts of a prolonged aspen leafminer outbreak on aspen in Alaska are still being studied.

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Control Measures

There are no effective control measures for large scale outbreaks of aspen leafminer (ALM). As with many leafmining insects, disease, parasitoids, and predators are believed to be the main causes of outbreak population crashes. Inadvertent cannibalism (one larvae chewing through another) can occur if larvae/leaf densities are high. Climate may influence ALM populations. Leaf mining insects tend to thrive in years associated with warm and dry weather. Thus, years with cold, wet weather may lower populations of ALM.

Survey Method

Ground and aerial survey.

Aspen Leafminer Damage Maps

Click maps for larger version.

Cumulative aspen leaf miner damage mapped by aerial and ground surveys with
modeled host tree distributions. Inset maps display areas mapped in 2020 using
remote sensing techniques based on high-resolution satellite imagery.

Aspen leafminer damage mapped by aerial survey in 2018 (240,000 acres; left map). The estimated
total area of aspen leafminer in the Interior in 2018 is 1.2 million acres (depicted in gray; right map).
The red polygon was created based on ~2,000 ground and aerial observations and covers 42 million
acres. This large damage polygon was then clipped using an aspen host layer to limit the estimated
area to aspen forests.

Resources & Publications

FS-R10-FHP. 2017. Forest Health Conditions in Alaska 2017. Anchorage, Alaska. U.S. Forest Service, Alaska Region. Publication R10-PR-43. 64 P. Available here

Condrashoff, S. 1964. Bionomics of the aspen leaf miner, Phyllocnistis populiella Cham. (Lepidoptera: Gracillariidae). The Canadian Entomologist 96:857-874. Available here

Doak, P., D. Wagner, and A. Watson. 2007. Variable extrafloral nectary expression and its consequences in quaking aspen. Botany 85:1-9. Available here

Wagner, D., L. DeFoliart, P. Doak, and J. Schneiderheinze. 2008. Impact of epidermal leaf mining by the aspen leaf miner (Phyllocnistis populiella) on the growth, physiology, and leaf longevity of quaking aspen. Oecologia 157:259-267. Available here

Wagner, D., P. Doak, T. Sformo, P. M. Steiner, and B. Carlson. 2012. Overwintering physiology and microhabitat use of Phyllocnistis populiella (Lepidoptera: Gracilliariidae) in Interior Alaska. Environ. Entomol. 41:180-187. Available here

Content adapted from Kruse, Ambourn, and Zogas, Aspen Leaf Miner leaflet, USDA Forest Service, Alaska Region, State and Private Forestry. R10-PR-14 June 2007. Available here

For more information about aspen leafminer, contact Interior Entomologist Sydney Brannoch, PhD, sydney.brannoch@usda.gov.

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