Balsam woolly adelgids only live on fir and spruce trees in forested areas. Their populations are largest in regions where the fir growth rate and quality are the highest. Higher adelgid populations are typically found at lower elevations, milder temperatures, near forest edges, and near mountain lakes and meadows. (Goheen and Willhite, 2006; Hrinkevich, et al., 2016; Sidebottom, 2019)
Balsam woolly adelgid adults are very small and have a covering of woolly wax that hides their body completely. This covering gives them the appearance of a tiny piece of cotton on tree bark. Underneath the covering, adults are about 0.5 to 1 mm long, soft-bodied, and dark purple or black in color. Nymphs are black and have an underdeveloped wax covering which grows as they mature. Eggs are oblong, amber-colored, and approximately 0.3 mm long. Crawlers look very similar to eggs but are slightly larger and have legs and eyes. (Goheen and Willhite, 2006; Ragenovich and Mitchell, 2006; Sidebottom, 2019; Varty, 1956)
Almost all balsam woolly adelgids go through five stages of development: Egg, crawler, two stages of nymph, and adult. The first stage is the egg, followed by crawlers, which are sometimes called neosistens. After settling, the crawler molts to a nymph. From there, nymphs molt two more times to reach adulthood. It takes approximately one month for a nymph to molt to an adult. In the wild, there are typically two generations per year, known collectively as sistens generations. These two sistens generations, heimosistens and aestivosistens, enter diapause (a period of dormancy and delayed development) during different seasons. Hiemosistens enter diapause in the winter. They hatch in the fall, settle, overwinter in the crawler stage, then continue development in the spring. Aestivosistens enter diapause in the summer. They hatch in the summer, settle, then aestivate as crawlers for three to six weeks before maturing. (Alston, et al., 2018; Montgomery and Havil, 2014; Sidebottom, 2019; Varty, 1956)
There is also a third generation of balsam woolly adelgids that is seldom seen in the wild called the progrediens generation. This generation hatches in the summer from eggs laid by hiemosistens. They typically hatch close to the beginning of the season, before or alongside the aestivosistens. Progrediens have six stages of development that are nearly identical those of the sistens generations, but with one extra nymph stage. Unlike the sistens generations, the progrediens generations do not go through a period of diapause. (Varty, 1956)
Balsam woolly adelgids are all female and reproduce solely through parthenogenesis. (Sidebottom, 2019)
Balsam woolly adelgids go through two to four generations each year, depending on temperature, climate, and elevation. Two generations is most common. The summer generation (aestivosistens) hatches in May through June. Aestivosistens reach maturity by July and their oviposition begins about a week after their final molt. The eggs laid by aestivosistens hatch in as little as a few days, depending on temperature. The spring generation (hiemosistens) hatches from these eggs. They then overwinter as crawlers and resume maturing in March or April, reaching adulthood in March through May. Balsam woolly adelgids have been observed laying up to 250 eggs in the lab, but only lay approximately 100 eggs in the wild. The first few eggs that hiemosistens lay produce progrediens, which almost always die before they can reproduce, but the vast majority of their eggs produce aestivosistens. (Alston, et al., 2018; Montgomery and Havil, 2014; Ragenovich and Mitchell, 2006; Sidebottom, 2019; Varty, 1956)
Balsam woolly adelgids do not take care of their offspring, but their wax coating may protect their eggs until they hatch. (Sidebottom, 2019)
The lifespan of balsam woolly adelgids varies across generations. Hiemosistens, the generation that overwinters as nymphs, lives the longest on account of their overwintering. The progrediens have the shortest lifespan, surviving only a few days in the wild. Neoprogrediens (progredientes crawlers) hatch in March through the beginning of May and can only feed on newly flushed leaves. These leaves do not appear until late May, so all neoprogrediens die of starvation. During spring and summer in Europe, adults can live for up to two months, but rarely live that long in the wild due to heavy predation. Extreme hot and extreme cold temperatures in North America may also shorten balsam woolly adelgid lifespans. (Sidebottom, 2019; Varty, 1956)
Balsam woolly adelgids are completely sedentary for almost their entire lives. The crawler life stage is the only stage that is capable of movement. Crawlers must locate a suitable place to feed within several days of hatching or they will starve. Once a crawler has found a feeding location, it settles, inserting its stylet into the tree. From this point it remains completely sedentary for the rest of its life. The sistens generations typically settle near the trunk of the tree. Crawlers can also be carried by the wind to another host tree. (Ragenovich and Mitchell, 2006; Sidebottom, 2019; Varty, 1956)
Balsam woolly adelgids spend almost their entire life on a single spot on a fir tree. (Sidebottom, 2019)
Balsam woolly adelgids have compound eyes for detecting light and can also detect temperature. They use these senses to help them find an optimal feeding location during the crawler stage. After the crawler stage, the adelgids keep their eyes but seem to have no further use for them. Balsam woolly adelgids have no known forms of social communication. (Sidebottom, 2019; Varty, 1956)
Balsam woolly adelgids feed exclusively on fir trees. To feed, these adelgids insert their long, tube-like mouthparts into the bark. They are most often found near the trunk of infested trees. In North America, they primarily feed on balsam firs (Abies balsamea), Fraser firs (Abies fraseri), subapline firs (Abies lasiocarpa), Pacific silver firs (Abies amabilis), and grand firs (Abies grandis). In Europe, they are known to feed on European silver firs (Abies alba). (Ragenovich and Mitchell, 2006)
Balsam woolly adelgids are prey to many animal species. Beetles in the genus Laricobus, the lady beetle genus Scymnus, and the fly family Chamaemyiidae are specialist predators on the adelgid family Adelgidae. Some of the most abundant generalist predators of balsam woolly adelgids are hover flies, mites, and lacewings. The majority of predation is on the eggs. Balsam woolly adelgids do not have any known anti-predator behavioral adaptations, but the waxy, wool-like covering on their back hides their real body from sight and helps them blend in with mosses and lichens on the tree bark. (Davis, et al., 2022; Humble, 1994; Mitchell and Wright, 1967; Montgomery and Havil, 2014; Ragenovich and Mitchell, 2006)
In North America, balsam woolly adelgids are an invasive species and a deadly parasite to true fir trees, including balsam firs, Fraser firs, subalpine firs, Pacific silver firs, and grand firs. Large adelgid infestations result in the tree producing abnormal wood, which prevents the tree from getting proper water and nutrients. This deficiency can kill a host tree in two to nine years. By killing and damaging these trees, balsam woolly adelgids also contribute to deforestation, which threatens other animal and plant species that are endemic to those forests, including at least two species that are already endangered and ten that are federal species of concern. In Europe, balsam woolly adelgids have a commensal relationship with fir and spruce trees, especially European silver firs. Because balsam woolly adelgids are native to Europe, these trees are resistant to adelgid infestations. (Boynton and Kelly, 2007; Goheen and Willhite, 2006; Hrinkevich, et al., 2016; Potter, et al., 2005)
Balsam woolly adelgids are prey to many other animal species. They provide easy nutrients for their predators, which ultimately helps support biodiversity in their environment. Generally, greater biodiversity indicates a healthier, more resilient ecosystem, which is beneficial for both wildlife and humans.
Balsam woolly adelgids cause severe economic costs to the Christmas tree industry. The majority of Christmas trees are fir trees, the primary hosts of balsam woolly adelgids. Infestations are difficult to spot unless the farmer knows where and what to look for. Furthermore, infested trees are economically inviable and must be culled to prevent further infestations. Treating an area for balsam woolly adelgids can also be very expensive, costing famers up to $500 per acre. (Potter, et al., 2005; Ragenovich and Mitchell, 2006)
There is insufficient data to determine the abundance of balsam woolly adelgids. Because they are considered invasive in North America, humans have made numerous attempts to control their populations through a variety of methods. The majority of these attempts have had seemingly little or no effect on balsam woolly adelgid populations. The few methods that are effective against balsam woolly adelgids are costly and unsustainable. (Alston, et al., 2018; Ragenovich and Mitchell, 2006; Sidebottom, 2019)
Balsam wooly adelgids are part of the Adelges piceae species complex. This complex consists of six adelgid species: Adelges piceae, Adelges nebrodensis, Adelges prelli, Adelges merkeri, Adelges schneideri, and Adelges nordmannianae. (Havill, et al., 2020)
Most adelgid species alternate between a primary host, which is a spruce tree, and an intermediate host, which is a fir tree. Sexual generations, which consist of both males and females and reproduce sexually, are only produced on the primary host. Balsam woolly adelgids do not have a primary host, so they do not have a sexual generation and must reproduce asexually. (Varty, 1956)
Balsam woolly adelgids are sometimes called silver fir adelgids in Europe. (Varty, 1956)
Balsam woolly adelgids from the progrediens generations can be either apterous (without wings) or alate (with wings). Alate progrediens develop wing pads as nymphs and have fully formed wings as adults. These wings are transparent and approximately 1 mm long. When alate progrediens survive to adults, they become motile again and fly to a new host tree as soon as their wings harden. On this new host, they settle for a second time and once again become completely sedentary. Alate progrediens have not been observed in the wild. (Varty, 1956)
Avery Gibson (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
living in landscapes dominated by human agriculture.
Referring to an animal that lives in trees; tree-climbing.
reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
A substance that provides both nutrients and energy to a living thing.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
An animal that eats mainly plants or parts of plants.
(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
development takes place in an unfertilized egg
remains in the same area
offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
uses sight to communicate
Alston, D., R. Davis, D. McAvoy, L. Spears, D. Malesky, L. Hebertson, C. Keyees. 2018. "Balsam Woolly Adelgid - Advanced Fact Sheet" (On-line). Accessed July 05, 2023 at https://digitalcommons.usu.edu/extension_curall/1838/.
Boynton, A., C. Kelly. 2007. "Carolina Northern Flying Squirrel" (On-line). NCpedia. Accessed July 07, 2023 at https://www.ncpedia.org/carolina-northern-flying-squirrel.
Davis, G., L. Lowrey, T. Eckberg, J. Hicke, E. Smirnova. 2022. Characterizing Balsam Woolly Adelgid Infestations and Associated Tree Mortality in Idaho. Journal of Forestry, 120(4): 361-378. Accessed July 10, 2023 at https://doi.org/10.1093/jofore/fvac007.
Goheen, E., E. Willhite. 2006. Field Guide to the Common Diseases and Insect Pests of Oregon and Washington Conifers. Portland, Oregon: USDA Forest Service, Pacific Northwest Region. Accessed July 02, 2023 at https://www.biodiversitylibrary.org/item/152991#page/5/mode/1up.
Havill, N., B. Griffin, J. Andersen, R. Foottit, M. Justesen, A. Caccone, V. D'Amico, J. Elkinton. 2020. Species Delimitations and Invasion History of the Balsam Woolly Adelgid, Adelges (Dreyfusia) piceae (Hemiptera: Aphidoidea: Adelgidae), Species Complex. Systematic Entomology, 46(1): 186-204. Accessed July 16, 2023 at https://doi.org/10.1111/syen.12456.
Hrinkevich, K., R. Progar, D. Shaw. 2016. Climate Risk Modelling of Balsam Woolly Adelgid Damage Severity in Subalpine Fir Stands of Western North America. PLOS ONE, 11(10): 1-11. Accessed July 02, 2023 at https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0165094.
Humble, L. 1994. Recovery of additional exotic predators of balsam woolly adelgid, Adelges piceae (Ratzeburg) (Homoptera: Adelgidae), in British Columbia. The Canadian Entomologist, 126(4): 1101-1103. Accessed July 09, 2023 at http://dx.doi.org/10.4039/Ent1261101-4.
Mitchell, R., K. Wright. 1967. Foreign Predator Introduction for Control of the Balsam Woolly Adelgid in the Pacific Northwest. Journal of Economic Entomology, 60(1): 140-147. Accessed July 09, 2023 at https://doi.org/10.1093/jee/60.1.140.
Montgomery, M., N. Havil. 2014. "The Use of Classical Biological Control to Preserve Forests in North America" (On-line). Accessed July 14, 2023 at https://www.fs.usda.gov/nrs/pubs/jrnl/2014/nrs_2014_montgomery_001.pdf#:~:text=It%20has%20two%20to%20four%20sistens%20%28diapausing%29%20generations,Balch%2C%201952%3B%20Varty%2C%201956%3B%20Mitchell%20et%20al.%2C%201961..
Potter, K., J. Frampton, J. Sidebottom. 2005. Impacts of Balsam Woolly Adelgid on the Southern Appalachian Spruce-Fir Ecosystem and the North Carolina Christmas Tree Industry. Third Symposium on Hemlock Woolly Adelgid in the Eastern United States, 1: 25-41.
Ragenovich, I., R. Mitchell. 2006. Forest Insect & Disease Leaflet 118: Balsam Woolly Adelgid. Washington, D.C.: U.S. Department of Agriculture Forest Service.
Sidebottom, J. 2019. "Balsam Woolly Adelgid" (On-line). NC State Extension. Accessed July 02, 2023 at https://content.ces.ncsu.edu/balsam-woolly-adelgid#section_heading_4932.
Varty, I. 1956. Adelges Insects of Silver Firs. West Bromwich, Great Britain: Her Majesty's Stationery Office. Accessed July 13, 2023 at https://cdn.forestresearch.gov.uk/1956/04/fcbu026.pdf.