Hemiberlesia ithacae (Ferris): Hemlock Scale

California Pest Rating for

Synonym: Abgrallaspis ithacae

Hemiptera: Diaspididae

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

On December 11, 2013 an official with Santa Cruz County contacted CDFA with questions regarding the risk associated with Abgrallaspis ithacae (Hemlock Scale). The current destruction of large numbers of Christmas wreaths due to the presence of the scale is considered punitive by some merchants. The insect is currently Q-rated, so a pest rating proposal is needed to determine future direction.

History & Status:

Background:

Hemlock scale feeds on the undersides of the needles of several species of trees. The scale is only known to feed on Canada balsam fir (Abies canadensis), grand fir (Abies grandis), Colorado blue spruce (Picea pungens), douglas fir (Pseudotsuga taxifolia), eastern hemlock (Tsuga canadensis), and western hemlock (Tsuga heterophylla). Hemlock scale has two generations per year and overwinters as second-instars.

Worldwide Distribution: Hemlock scale is native to North America. It is confirmed to be in Indiana, Maryland, New York, and Virginia². It is also reported from Connecticut, Georgia, Ohio, Pennsylvania, Tennessee, and West Virginia². There are also published records from Idaho, Montana, Washington, and Oregon; however, these records are reported to be incorrect².

Official Control: Hemlock scale is not known to be under official control in any states or nations.

California Distribution: Hemlock scale has never been found in the environment of California.

California Interceptions: Hemlock scale is often intercepted on shipments of Christmas wreaths, trees, and plants.

The risk hemlock scale (Abgrallaspis ithacae) would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Hosts of hemlock scale are restricted to the cooler parts of California but may also be grown elsewhere as ornamentals. The scale receives a Medium(2) in this category.

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

– 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: Hemlock scale feeds on trees in four genera in one plant family. The scale receives a Low(1) in this category.

Evaluate the host range of the pest. Score:

– 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: Armored scales can reproduce rapidly and may be transported long distances through the trade of nursery stock. However, females have limited mobility so the trade in plant parts that are not for planting is not high risk for introducing the scale. It is likely that infested Christmas trees and wreaths will be disposed of as green waste, some of which may end up as mulch. However, the limited host range of this scale reduces the likelihood that the mulch will end up in close proximity to living host plants. Furthermore, hemlock scale overwinters as second instars. It is likely that cut trees and wreaths shipped in late fall and early winter will dry out before spring, reducing their viability as host material and eliminating the possibility of overwintering second instars completing development. Hemlock scale receives a Medium(2) in this category.

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

– 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: Heavy infestations of hemlock scale are reported to cause early leaf drop, dieback of branches, and defoliation of trees². This reduces vigor and severe infestations result in death of trees³. This has the potential to lower yield and crop value and increase production costs at Christmas tree farms and some forests. Hemlock scale receives a Medium(2) in this category.

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

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.

– 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: Hemlock scale is not expected to lower biodiversity, disrupt natural communities, or change ecosystem processes. The scale is not known to feed on any plants in genera that contain threatened or endangered species in California. Hemlock scale is not expected to disrupt critical habitats. The scale could trigger some additional official or private treatment programs in Christmas tree farms or forests^2,3. The scale is not expected to significantly impact cultural practices, home/urban gardening, or ornamental plantings. Hemlock scale receives a Medium(2) in this category.

Evaluate the environmental impact of the pest on California using the criteria below.

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 or endangered species 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.

Score the pest for Environmental Impact. Score:

– 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 Hemlock Scale (Abgrallaspis ithacae): Medium(9)

Add up the total score and include it here.

–Low = 5-8 points
–Medium = 9-12 points
–High = 13-15 points

6) Post Entry Distribution and Survey Information: Hemlock scale has not been found in the environment of California. It receives a Not established(0) in this category.

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

–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:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: Medium(9)

Uncertainty:

It is possible that hemlock scale could jump to new hosts in California. It is also possible that hemlock scale may be managed by existing IPM programs in Christmas tree farms.

Conclusion and Rating Justification:

Hemlock scale may have limited economic impacts to Christmas tree farms and forests. The environmental impacts of the scale are expected to be limited to possible chemical treatments of the scale in Christmas tree farms and managed forests. A “B”-rating is justified.