Thysanofiorinia nephelii (Maskell): Longan Scale

California Pest Rating for
Thysanofiorinia nephelii (Maskell): Longan Scale
Hemiptera: Diaspididae
Pest Rating:  B

 


PEST RATING PROFILE
Initiating Event:

August 23, 2012 Ron Eng (CDFA) requested a permanent rating for longan scale (Thysanofiorinia nephelii) as follow-up to a find of the Q-rated pest on a longan tree in a nursery in Santa Ana.

History & Status:

Background:  Longan scale is an armored scale insect that is sometimes considered a pest of the tropical fruits longan (Dinocarps longan) and lychee (Litchi chinensis).  In addition to those primary hosts it has also been occasionally recorded on other hosts:  “Kentia sp.” (a palm), “Cassia” (a leguminous tree), Euphorbia longena (a spurge), and Indigofera sp. (a flowering plant) (SEL).  Longan scale may be spread long distances by the movement of infested plants and fruit.

Worldwide Distribution: Longan scale is believed to be native to mainland Asia (India to China) but has invaded Australia, Japan, Taiwan, the Northern Mariana Islands, Brazil, Cuba, Algeria, and Hawaii (sometime before 1932).  It was first detected in Florida, the nation’s leading producer of longan and lychee fruit, in 1996 and considered an emerging pest.  Although it had spread to seven counties by 2007, there were no reports of significant economic damage (Suh et.al. 2007).

Official Control:  Thysanofiorinia nephelii is not known to be under official control in any other states or nations.  The scale was downgraded to non-actionable by USDA in March 2011.

California Distribution:  Longan scale has never been collected in the environment in California.

California Interceptions This scale was found in regulatory situations by CDFA 164 times between 1992 and August 2012.  The majority of these were interceptions of crawlers (the 1st instar nymphs) on longan and lychee fruit purchased out of state.  The scale has also been found 5 times on trees in nurseries.

The risk Thysanofiorinia nephelii (longan scale) would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Longan scale has not spread beyond southern Florida since it established there. Longan and lychee are only grown in limited areas of Southern California and the scale would probably be restricted to those areas if it were to enter the state.  Longan scale receives a Low (1) rating for 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: Longan scale feeds primarily on longan and lychee, two tropical sapindaceous fruit trees in two different genera.  However, it has also been reported on four other hosts in three different plant families.  Longan scale receives a Medium (2) for host range.

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: Scale insects have high reproductive rates.  Crawlers of longan scale have been intercepted on longan and lychee fruit many times and may be able to disperse through this pathway.  However, fruit would have to be disposed of in close proximity to a host tree.  Adult female longan scales have been detected on trees in nurseries.  This pathway is how the longan scale is thought to have spread within Florida (Suh et. al. 2007) and is the highest risk pathway for spread within California.  Due to its ability to move long distances through nursery stock longan scale 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: California has approximately 23 ha of longan and lychee orchards (Crane et. al. 2005) worth an estimated $500,000 annually.  Additionally, there is a market for longan and lychee nursery stock in Southern California.  Furthermore, discussions on internet forums indicate there is interest among residents in growing more longan and lychee fruit in the state.  However, no major economic damage has been reported from the introduction of this scale to Florida’s industry.  Longan scale is not expected to lower yields on these trees but it could increase production costs in some cases by triggering chemical treatment.  It is presumed that the fruits grown in California are produced for domestic consumption so no export issues are considered.  Longan scale is not known to vector any pathogens, injure animals, or interfere with water supplies.  Longan scale receives a Low (1) for economic impact.

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: Longan scale is not expected to lower biodiversity, disrupt natural communities, or change ecosystem processes.  There are no plants listed in California’s threatened and endangered plant list from the genera listed as hosts for the scale (Dinocarps, Litchi, Kentia, Euphorbia, Cassia, or Indigofera).  The scale is not expected to disrupt critical habitats.  Although the scales are often controlled by natural enemies in Florida they do sometimes reach high populations that require additional treatment programs.  The scale is not expected to significantly change cultural practices, home/urban gardening, or ornamental plantings.  Longan scale receives a Medium (2) for environmental impact.

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 Thysanofiorinia nephelii (Longan Scale): 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: Longan scale has never been found in the environment of California and 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:  Medium(9)

Uncertainty:

A variety of ants that tend Homoptera, such as longan scale, are abundant in California.  Ants could protect the scales from natural enemies, causing them to reach higher populations more rapidly than in Florida, thereby triggering more chemical treatments.  The market for Asian fruit is expanding in the United States.  Although lychee and longan do not thrive in California at present, changes in technology or the environment could change this in the future.  If lychee and longan production were to expand in California in the future then longan scale may become a more damaging insect.  Furthermore, the possibility exists that longan scale could colonize additional host plants in California.

Longan scale was intercepted in regulatory situations 164 times between 1992 and 2012.  Presumably the scale enters California many additional times and is not intercepted.  Since it has never been found in our environment, it is possible that environmental conditions (such as the lack of humidity) preclude its establishment.  Alternatively, it is possible that the scale is already here and no one has looked for or noticed it.

Conclusion and Rating Justification:

Evidence suggests that the introduction of Longan Scale would be of low economic consequences to California.  Despite the scale’s invasive nature and ability to travel in international and domestic trade of longan and lychee fruit and nursery stock, there is only one scientific paper in the literature that mentions its pest potential.  It has not had major economic consequences since its detection in Florida in 1996.  The pest has a limited host range and would probably not affect the environment of California, with the exception of possible additional treatments by longan and lychee growers.

Evidence also suggests that the introduction of longan scale to California is highly likely to happen.  It has been detected in regulatory situations many times.  It is likely to survive post-harvest treatments and shipment to California.  Due to the small size of crawlers and immobility of adults it is likely to at least occasionally escape detection by inspectors.  It is capable of living on and spreading through nursery stock and is likely to be introduced to favorable environments for establishment through that pathway.

The scale has never been detected in the environment of California.  Additionally, rare fruit markets are expanding and we do have a small commercial longan and lychee fruit industry that may be affected by the pest.  Therefore, it is recommended that the permanent pest rating be set to “B”.

References:

Crane, J.H., Zee, F., Bender, G.S., Faber, B., Brunner, B. and Chia, C.L. 2005. COMMERCIAL

SAPINDACEOUS FRUIT PRODUCTION IN THE USA. Acta Hort. (ISHS) 665:93-104

http://www.actahort.org/books/665/665_11.htm

Suh, S.J., G. S. Hodges, and A. C. Hodges.  2007.  Notes on the Longan Scale, Thysanofiorinia nephelii (Hemiptera: Coccoidea: Diaspididae) in Florida.  Florida Entomologist 90(2): 407-409.  http://journals.fcla.edu/flaent/article/view/75670/73328

SEL:   http://www.sel.barc.usda.gov/catalogs/diaspidi/Thysanofiorinianephelii.htm


Responsible Party:

Jason Leathers, 1220 N Street, Sacramento, CA, 95814, (916) 654-1211, plant.health[@]cdfa.ca.gov.


Comment Period:  CLOSED

The 45-day comment period opened on March 8, 2016 and closed on April 22, 2016.


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Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

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Pest Rating:  B


Posted by ls