Animal Diversity Web

Ge­o­graphic Range

Bal­sam woolly adel­gids (Adelges piceae) are na­tive to cen­tral Eu­rope and are thought to have spread to North Amer­ica in the early twen­ti­eth cen­tury. In North Amer­ica, these adel­gids are pri­mar­ily found in the Ap­palachian Moun­tains and north­east­ern United States. (Go­heen and Will­hite, 2006; Hrinke­vich, et al., 2016; Side­bot­tom, 2019)

• Biogeographic Regions
• nearctic
  • introduced
• palearctic
  • native

Habi­tat

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)

• Habitat Regions
• temperate
• terrestrial

• Terrestrial Biomes
• forest

• Other Habitat Features
• agricultural

Phys­i­cal De­scrip­tion

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)

• Other Physical Features
• ectothermic
• bilateral symmetry

• Range length

  0.5 to 1 mm

  0.02 to 0.04 in

De­vel­op­ment

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)

• Development - Life Cycle
• metamorphosis
• diapause

Re­pro­duc­tion

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)

• Key Reproductive Features
• semelparous
• parthenogenic
• asexual
• oviparous

• Range eggs per season

  250 (high)

• Average eggs per season

  100

Bal­sam woolly adel­gids do not take care of their off­spring, but their wax coat­ing may pro­tect their eggs until they hatch. (Side­bot­tom, 2019)

• Parental Investment
• no parental involvement

Lifes­pan/Longevity

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)

Be­hav­ior

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)

• Key Behaviors
• arboreal
• parasite
• sedentary

Home Range

Bal­sam woolly adel­gids spend al­most their en­tire life on a sin­gle spot on a fir tree. (Side­bot­tom, 2019)

Com­mu­ni­ca­tion and Per­cep­tion

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)

• Perception Channels
• visual
• infrared/heat

Food Habits

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)

• Primary Diet
• herbivore
  • eats sap or other plant foods

• Plant Foods
• sap or other plant fluids

Pre­da­tion

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)

• Anti-predator Adaptations
• cryptic

• Known Predators

  • Laricobius erichsonii
  • Pullus impexus
  • Larch ladybird (Aphidecta obliterata)
  • Aphidoletes thompsoni
  • Cremifania nigrocellulta
  • Leucopis obscura
  • Tooth-necked fungus beetle (Laricobius nigrinus)
  • Tooth-necked fungus beetle (Laricobius rubidus)
  • Leucopis pinicola
  • Leucopis ancilla
  • Silver fly (Leucopis argenticollis)
  • Red velvet mite (Allothrombium mitchelli)
  • Nebulous lady beetle (Scymnus nebulosus)
  • Scymnus nebulosus
  • Brown lacewing (Hemerobius humulinus)
  • Hairy-eyed flower fly (Syrphus torvus)
  • Leucopis americana
  • Tetraphleps canadensis
  • Harvester butterfly (Feniseca tarquinius) larvae
  • Whirlgig mites (Anystis sp.)
  • Leptus sp.
  • Green lacewing (Chrysoperla sp.)

Ecosys­tem Roles

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)

• Ecosystem Impact
• parasite

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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.

• Positive Impacts
• food

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

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)

• Negative Impacts
• crop pest

Con­ser­va­tion Sta­tus

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)

• IUCN Red List

  Data Deficient No special status

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Other Com­ments

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)

Con­trib­u­tors

Avery Gib­son (au­thor), Col­orado State Uni­ver­sity, Tanya Dewey (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

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.