Howardia biclavis (mining scale)

California Pest Rating for
Howardia biclavis (mining scale)
Hemiptera: Diaspididae
Pest Rating: A

Initiating Event:

Howardia biclavis has an internal CDFA rating of A.
A pest rating proposal is required to support an official pest rating.

History & Status:

Background:  Howardia biclavis is an armored scale insect. It reproduces parthenogenetically without males 2. The number of days for each developmental stage and number of generations per year depend on temperature, humidity and rain fall 3. Howardia biclavis completes its life cycle in 30 days. It infests the bark, leaves and fruit of the host plant by burrowing beneath the epidermal layer. It has a wide host range covering 68 families (194 genera). Recorded hosts include acacia, allamanda, bougainvillea, cassia, fig, ebony, gardenia, hibiscus, ixora, jasmine, kelumpang, lantana, lychee, mango, papaya, plumeria, poinsettia, pulasan, sapodilla, and sapote 4.

Worldwide Distribution: Howardia biclavis is thought to be originated in the New World tropics 7 or Africa 8. It is now found worldwide and has been reported in 71 countries 4. In the Unites States, it was first recorded at Kona, Hawaii in 1895 by Maskell 1.

Official Control: Howardia biclavis has been listed as a harmful organism by Chile, French Polynasia, Republic of Korea, Mexico and Taiwan 5.

California Distribution:  Howardia biclavis was found in California Nurseries prior to 1950 and was eradicated by 1956. It was eradicated subsequently whenever found 9. Based on CDFA pest and damage records database, it has not been detected in California’s natural or agricultural environment between January 2000 through August 2016 10.

California Interceptions:  Howardia biclavis has been intercepted multiple times through border station inspections, dog teams and high risk pest exclusion activities. Between January 2000 and August 2016, it has been intercepted 116 times 10.

The risk Howardia biclavis (Mining scale) would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Host plants of Howardia biclavis are grown throughout California and this presents the possibility of rapid spread and establishment of this pest within the state. It receives a High (3) 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: Howardia biclavis is highly polyphagous and its host range includes 68 plant families covering 194 genera of plants 4. It receives a High (3) 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: Howardia biclavis reproduces parthenogenetically and completes its life cycle in 30 days. The crawler stage of this insect can be easily transported by people, animals, birds, ants and wind currents. Wind also acts as a dispersal agent. Long distance dispersal happens by passive transport of infested material and short distance dispersal occurs when crawlers search out places to settle and feed. It receives a High (3) 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: Howardia biclavis is expected to lower crop value because it feeds on plant juices and causes loss of vigor, deformation of infested plant parts, loss of leaves and sometimes death of plants. As armored scale are chiefly spread by movement of nursery stock, possibly resulting in quarantine triggers and loss of markets for California grown nursery stock. Mining scale has been reported as an economic pests of woody ornamentals in Florida. It is considered a serious world pest. It receives a High (3) 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: Howardia biclavis causes deformation of infested plants. Growers can find the infested plants unsightly. This would significantly impact cultural practices, urban gardening and ornamental plantings. Growers would need additional residential pesticide treatments if it were to infest the urban and ornamental plant environment. It receives a High (3) 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 Mining Scale:  High (15)

Low = 5-8 points

Medium = 9-12 points

High = 13-15 points

6) Post Entry Distribution and Survey Information: Howardia biclavis has not been found and established in natural environment of California. Therefore, it receives a Not Established (0) 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.

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: (15)


Howardia biclavis has been intercepted many times by CDFA. There is a possibility that it may have entered the State and gone undetected. If it goes undetected, there is a good possibility that it will establish on its wide host range.

Conclusion and Rating Justification:

Howardia biclavis has been found in nurseries in California in the 1950’s and was eradicated. It has not been found in the natural environment in the last 15 years, but if it were to become established in the State, there would be significant economic and environmental impacts. Based on all the above evidence presented, an “A” rating is justified.


Tenbrink, Victoria L. and Hara, Arnold H. 1992. Hawaii Crop Knowledge Master: Howardia biclavis (Comstock). Accessed: 9/28/2016

Brown, S.W. 1965. Chromosomal survey of the armored and palm scale insects (Coccoidea: Diaspididae and Phoenicococcidae) Hilgardia 36: 189-294.

Beardsley, J. W. Jr. & R. H. Gonzalez. 1975. The biology and ecology of armored scales. Annual Review of Entomology 20: 47-73.

Scale net database: Howardia biclavis (Comstock), Accessed 9/30/2016

USDA Phytosanitary Certificate Issuance & Tracking System (PCIT): Phytosanitary Export Database (PExD), Accessed 9/28/2016

Invasive Species Compendium: Distribution maps for plant pests, Accessed 9/30/2016

Miller, D.R. Davidson, J.A. 2005 Armored Scale Insect Pests of Trees and Shrubs. Cornell University Press. xiv + 442 pp.

Watson, G.W. 2002 Arthropods of Economic Importance: Diaspididae of the World: Howardia biclavis (mining scale), Accessed 9/29/2016

Gill, Raymond J. 1997: The Scale Insects of California: Part 3: The Armored Scales (Homoptera Diaspididae). California Department of Food and Agriculture, Technical Series in Agricultural Biosystematics and Plant Pathology, 3: 307 pp.

10 Pest and Damage Report Database: Plant Health and Pest Prevention Services, California Department of Food and Agriculture: Accessed 9/30/2016

Responsible Party:

Raj Randhawa, Senior Environmental Scientist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 654-0312;[@]

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Pest Rating: A

Posted by ls