Adelges piceae: Balsam Woolly Adelgid

California Pest Rating for
Adelges piceae:  Balsam Woolly Adelgid
Hemiptera: Adelgidae
Pest Rating: B

Initiating Event:

Adelges piceae has been detected by CDFA in Mendocino County and has a temporary rating of “Z”. A pest rating proposal is required to support its permanent pest rating.

History & Status:

Background: Adelges piceae is a tiny, non-flying, sucking, soft-bodied insect which appears as a white, woolly spot on true firs3. Adults are blackish purple, roughly spherical in shape, less than 1mm long and produce a thick mass of wool-like waxy strands over their bodies. The first immature motile stage of this insect is known as a crawler. The crawlers are orange in color with legs and black eyes. The crawler is the only mobile stage in its life cycle and it is capable of crawling more than 30 m. Adelges piceae has 2-3 generations per year over most of its range with an occasional fourth generation1.

Adelges piceae has long, tube-like mouthparts, and causes great damage to fir forests in Canada and the United States. It was introduced into North America from Europe in the 1900s1. It is a serious pest to landscape and to the Christmas fir tree industry. Adelges piceae causes significant damage to true firs including Abies alba, A. balsamea, A. cilicica, A. fraseri, A. grandis, A. nordmanniana, and others. It is invasive outside of its native central Europe from where it spread via timber imports. Adelges piceae populations in North America are composed entirely of females and as a result, its reproduction is parthenogenetic (i.e. without mating and fertilization)3.

In Europe, host trees are relatively insensitive to attack and the insect is not considered a significant forest pest. In North America, however, it has caused significant damage and mortality to true firs (Abies spp.) in both eastern and western forests. In some localities, firs are slowly being eliminated from the ecosystem; and Adelges piceae populations continue to spread to previously uninfested areas2.

Worldwide Distribution: Adelges piceae is native to Europe where it is well distributed in Albania, Austria, Bosnia-Hercegovina, Bulgaria, Czechoslovakia, Denmark, France, Germany, Greece, Ireland, Italy, Lithuania, Macedonia, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Sweden, Switzerland and UK. In Asia it is present in Turkey. In North America it is introduced in Canada and USA. In South America it is invasive in Chile4.

In the United States it can be found in California, Idaho, Maine, New York, North Carolina, Oregon, Tennessee, Virginia, and Washington, West Virginia4.

Official Control: Adelges piceae is listed as a harmful organism in Canada, Japan, Guatemala and Ecuador 5.

California Distribution: Adelges piceae was first detected in California in 1928 in the SF Bay Area. Since then, according to Jack Marshall (CA Dept Forestry & Fire Protection, CA Forest Pest Council, 2012), it has been collected in Palo Alto (1934), Berkeley (1958), Sacramento (1986), and Mendocino Co. (2011, 2012)4.

California Interceptions: Adelges piceae was collected by State fire dept. in Mendocino County (PDR MVAP06099309)6.

The risk Adelges piceae (Balsam woolly adelgid) would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Hosts plants of Adelges piceae are grown on a limited part of California and this insect presents the possibility of spread and become established wherever the hosts are grown within the state. It receives a Medium (2) in this category.

Evaluate if the pest would have suitable hosts and climate to establish in California: Score: 2

Low (1) Not likely to establish in California; or likely to establish in very limited areas.

Medium (2) may be able to establish in a larger but limited part of California.

High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: Adelges piceae feeds on fir (Abies spp.) and some other pine species which are present only in high elevation. It has moderate host range. So it receives a Medium (2) in this category.

Evaluate the host range of the pest: Score: 2

Low (1) has a very limited host range.

Medium (2) has a moderate host range.

High (3) has a wide host range.

3) Pest Dispersal Potential: Adelges piceae females produce up to 200 eggs per clutch and normally two clutches produced per year2. Adelges piceae eggs and newly hatched nymphs are spread by wind, on animals and the movement of infested plant material. It receives a High (3) in this category

Evaluate the natural and artificial dispersal potential of the pest: Score: 3

Low (1) does not have high reproductive or dispersal potential.

Medium (2) has either high reproductive or dispersal potential.

High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Adelges piceae is a major pest of fir species and causes a billion feet of fir timber loss in North America. It is a serious pest to seed production, landscape fir, natural fir, and fir Christmas tree industry. It is listed as an invasive pest by Canada & Japan so it has the potential to trigger a loss of markets. It can increase production costs to growers if they perform any treatment to control its infestation. It receives a High (3) in this category

Evaluate the economic impact of the pest to California using the criteria below:  

Economic Impact: A, B, C

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

Low (1) causes 0 or 1 of these impacts.

Medium (2) causes 2 of these impacts.

High (3) causes 3 or more of these impacts.

5) Environmental Impact: Adelges piceae is not expected to lower biodiversity, disrupt natural communities, or change ecosystem processes.  Adelges piceae is not expected to directly impact threatened or endangered species. It could impact the habitat of endangered species Zayante band-winged grasshopper which feed on grass grown at the base of pines forest. Adelges piceae may trigger new chemical treatments in forests and the nursery industry.  It is not expected to have significant impacts on cultural practices, home/urban gardening, or ornamental plantings. Adelges piceae receives a High (3) in this catego

Evaluate the Environmental impact of the pest to California using the criteria below:  

Environmental Impact:  C, D

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened endangered species or by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 3

Low (1) causes none of the above to occur.

Medium (2) causes one of the above to occur.

High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Adelges piceae:  High (13)

Low = 5-8 points

Medium = 9-12 points

High = 13-15 points

6) Post Entry Distribution and Survey Information: Adelges piceae has a localized distribution in California, or is established in one suitable climate and receive Low Score (-1) in this category.

Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included: Score -1

Not established (0) Pest never detected in California, or known only from incursions.

Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

The final score is the consequences of introduction score minus the post entry distribution and survey information score: Medium (12)


Adelges piceae is introduced in California about 90 years ago; luckily it spread only a very limited area. Since, the host plants are growing on higher elevations and foot hills. Therefore, it is a strong possibility that it can be establish in other new areas of California.

Conclusion and Rating Justification:

Adelges piceae has been established in   Northern coastal area of California especially, in Mendocino County and is not under official control. Its establishment in the state is likely to have significant economic impacts to nurseries that produce and distribute Christmas trees. It is also likely to have environmental impacts as it triggers new chemical treatments and significantly affects ornamental plantings.  A “B” rating is justified.

  1. Amman, Gene D. 1962. Seasonal biology of the balsam woolly aphid on Mt. Mitchell, North Carolina. J. Econ. Entomol. 55(1):96-98. Accessed on 11-15-16
  1. Global Invasive Species Database (GISD) 2015. Species profile Adelges piceae National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG). Accessed on 11-23-16
  1. Hain, F.P. (1998). The balsam woolly adelgid in North America. pp 87-109. In: Ed. Berryman, A.A. Dynamics of Forest Insect Populations: Patterns, Causes, Implications, Plenum and New York.
  1.  Invasive Species Compendium: Distribution maps for plant pests
  1. USDA Phytosanitary Certificate Issuance & Tracking System (PCIT) Phytosanitary Export Database (PExD).
  1. Pest and Damage Record Database, California Department of Food and Agriculture, Plant Health and Pest Prevention Services.

Responsible party:

Javaid Iqbal,  California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 403-6695;[@]

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Pest Rating: B

Posted by ls