Dendrothrips howei Mound | Lord Howe Island Thrips | Pest Rating Proposals and Final Ratings

California Pest Rating for

Dendrothrips howei Mound: Lord Howe Island Thrips

Thysanoptera: Thripidae: Dendrothripinae

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

Dendrothrips howei has been recently found in Contra Costa County in a sample submitted by a property manager in Concord, California. This species was first found in 2010 in nurseries at Los Angeles and Riverside counties and outdoors in 2012 in Riverside and Orange counties. Currently, this pest has a temporary Q rating. A pest rating proposal is required to assign a permanent rating for this species.

History & Status:

Background: The subfamily Dendrothripinae is characterized by the thoracic structure and jumping abilities of the adults and it comprises a world fauna of 10 genera and more than 90 species. Members of Dendrothripinae differ from other Thripidae by the possession of lyre shaped spurs extending from the thorax (1, 3). All of these species live on young leaves, and they are usually small and jump when disturbed (2).

There are 52 species listed in genus Dendrothrips, none of which is native to any part of United States. Most of these species are known from Africa and Asia. Nine species are endemic to Europe and four from Australia. Dendrothrips howei is native to eastern Australia (4). The metamorphosis of thrips species is intermediate between simple and complete. Main hosts associated with this species include Xylosma species, Smilax australis and Trophis scandens. Eggs are laid in plant tissue or in crevices or under bark. Dendrothrips howei breeds in leaves but it is not known to vector viruses in its host plants.

Worldwide Distribution: Dendrothrips howei is native to eastern Australia and was first recorded in Long Howe Island in 1999 (4).

Official Control: Dendrothrips howei is not known to be under official control by any other states or nations. However, in Japan, all Thripidae are listed as harmful organisms (6).

California Distribution: Dendrothrips howei was first found in a nursery in Los Angeles in 2010 and by 2012, it was considered established and causing damage to its host plants (5). It has been confirmed in the environment of San Jacinto (Riverside County – PDR 1590230), Anaheim (Orange County – PDR 300P06040111), and Concord (Contra Costa County – PDR 070P06224306).

California Interceptions: There have been 18 records of Dendrothrips howei by CDFA through nursery regulatory activities and border station pathways between 2010 and 2016 (5).

The risk Dendrothrips howei would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Xylosma species, the main hosts of Dendrothrips howei, is grown as ornamental shrub in California. Xylosma is propagated in California nurseries and is sold as a pot plants at retail centers. Lord Howe island thrips will receive a High (3) in this category

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

Score: 3

– 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: Dendrothrips species are commonly associated with members of Oleaceae family (3). However, Dendrothrips howei is known to feed mainly on Xylosma maiden and Xylosma congestum (Salicaceae). Adults have also been recorded on Trophis scandens (Moraceae) and Smilax australis. It receives a Low (1) in this category.

Evaluate the host range of the pest:

Score: 1

– 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: Thrips have a rapid reproduction rate as one generation is completed in 15-28 days depending on the host and thrips species (7). Members of sub family Dendrothripinae are often highly active, and may jump readily when even slightly disturbed. Dendrothrips howei has become established in California feeding on leaves of Xylosma (Salicaceae). It has a high dispersal potential. The horticultural trade of its host plants continues to be a major pathway for dispersal of various thrips species (4). 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: Dendrothripinae are all leaf feeding insects, commonly associated with young leaves. Dendrothrips howei feeds on leaves and can cause distortion of new growth of host plants. This species is however not known to vector any viruses. This species may lower the quality and value of nursery grown Xylosma species by feeding on new growth and disfiguring plants. It receives a Medium (2) in this category.

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

Economic Impact: A, B

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 use

Economic Impact Score: 2

– 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: The establishment of Dendrothrips howei in California nurseries and landscapes is likely to trigger additional chemical treatments. Since Xylosma species are used as an ornamental plant in urban and residential areas, the establishment of Dendrothrips howei may impact cultural practices in homes and urban gardening plantings. Residents can be expected to treat or prune off distorted new growth on host plants. It receives a High (3) in this category.

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

Environmental Impact: D, E

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:

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 Dendrothrips howei (Lord Howe Island Thrips): Medium (12)**

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: Dendrothrips howei has been confirmed from the environment of Riverside and Orange counties, and recently at a non-contiguous area in Contra Costa County. It is likely to have become established in these areas and appears to have a widespread distribution in the state. It receives a High (-3) 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: 3

-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:

Dendrothrips howei has been found first in nursery regulatory inspections and then outdoors in certain areas of California. Most of the interceptions have been reported on containerized Xylosma plants. There have been no formal surveys done for the presence of this species in the state. Since Xylosma species are commonly used as ornamental plants in the state, it is likely that Dendrothrips howei is more widespread in California than currently recorded.

Conclusion and Rating Justification:

Impacts of Dendrothrips howei are likely to be limited to Xylosma species in California. As this species expands its distribution in California, cultural practices and possible chemical treatments would have significant environmental impacts. A “B” rating is justified.

References:

Hoddle MS, Mound LA & Paris DL. 2012. Thrips of California 2012. CBIT Publishing, Queensland, Australia. http://keys.lucidcentral.org/keys/v3/thrips_of_california/Thrips_of_California.html.

Hoddle MS, Mound LA and Nakahara S. Thysanoptera Recorded from California, USA: A Check List. Florida Entomologist 87 (3): 317-323. 2004 http://www.bioone.org/doi/full/10.1653/0015-4040(2004)087%5B0317%3ATRFCUA%5D2.0.CO%3B2

Mound LA (1999), Saltatorial leaf-feeding Thysanoptera (Thripidae, Dendrothripinae) in Australia and New Caledonia, with newly recorded pests of ferns, figs and mulberries. Australian Journal of Entomology 38: 257–273 http://onlinelibrary.wiley.com/doi/10.1046/j.1440-6055.1999.00112.x/full

World Thysanoptera. Identifying Thrips. Dendrothrips howei: Recognition Data. Commonwealth Scientific and Industrial Research Organization (CSIRO) http://anic.ento.csiro.au/thrips/identifying_thrips/Dendrothrips_howei.htm

Pest and Damage Records, Plant Health and Pest Prevention Services, California Department of Food and Agriculture. Accessed: 01/04/2017 http://phpps.cdfa.ca.gov/user/frmLogon2.asp

USDA Phytosanitary Certificate Issuance & Tracking System (PCIT) Phytosanitary Export Database (PExD). https://pcit.aphis.usda.gov/pcit/

Featured Creatures: University of Florida. Entomology and Nematology http://entnemdept.ufl.edu/creatures/

Responsible Party:

Raj Randhawa, Senior Environmental Scientist; Dean G. Kelch, Primary Botanist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 654-0312; plant.health[@]cdfa.ca.gov.

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