Bruchidius terrenus: Seed Beetle

California Pest Rating
Bruchidius terrenus: Seed Beetle
Coleoptera: Chrysomelidae
Former Pest Rating:  Q
Current Pest Rating: B
Initiating Event:

Bruchidius terrenus, seed beetle, has a current rating of Q. It has been recently identified at the CDFA -Plant Pest Diagnostics Center on November 1, 2016 from an Albizia tree seed pod sample submitted from Mendocino County. This is the second time that this beetle has been found at the same location. The first time, the sample was collected on October, 2015 and was identified morphologically as Bruchidius species and Tuberculobruchus species via molecular method. The second find at the same site after a year has prompted this risk analysis to establish a permanent rating for this species.

History & Status:

Background: Bruchidius terrenus is a specialist seed predator of Albizia julibrissin (Mimosa tree). Adult beetles probably overwinter near host trees in plant litter. These overwintered, sexually immature adults emerge in the Southeastern U.S. in late spring and disperse to mimosa trees where they feed on pollen. Oviposition begins in early July when green pods are formed. Eggs are laid individually on young pods and hatch in 1-2 weeks. The larva emerges from the underside the pod and tunnel into developing pods. The number of instars are inferred to be four. Pupation occurs within the seed inside the closed pod and the pupal period takes 10-20 days. New generation adults chew through the seed coat and then through the pod coat to emerge in early September and feed on pollen in the fall. Bruchidius terrenus reduces seed production of the host plant. In addition to mimosa trees, it also feeds on acacia and black locust (1). Continuous spread likely can occur with infested nursery stock or seeds.

Worldwide Distribution: Bruchidius terrenus occurs widely in the eastern Palearctic region of China, Japan and Taiwan.

United States: Bruchidius terrenus has been recorded in the southeastern states of Alabama, Florida, Georgia, Mississippi, North Carolina, South Carolina and Tennessee.

Official Control: Bruchidius species are listed as harmful organisms in Brazil, Chile and India.

California DistributionBruchidius terrenus has been found twice at the same location in Mendocino County.

California Interceptions: Bruchidius terrenus has not been intercepted in any regulatory situations in California.

The risk Bruchidius terrenus would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Albizia julibrissin (Mimosa tree), the main host of Bruchidius terrenus, grows in gardens, disturbed areas like roadsides, forest edges and various open habitats. This plant can tolerate a variety of soil and moisture conditions. It is sparingly naturalized and widely distributed throughout California (4, 5). Mimosa tree is reported as one of the best-selling ornamental trees in southern California (3). Therefore, Bruchidius terrenus is likely to establish in all areas of California where Mimosa trees are grown. 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: Bruchidius terrenus primarily feeds on mimosa tree, acacia and black locust (1). It has also been detected on Cornus foemina, Hydrangea quercifolia and Solidago sp. nationally, but these species are not known to be true hosts. It 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: Bruchidius terrenus is a univoltine species with just one brood of offspring per year. The eggs are laid individually on young seed pods. Emerging larva tunnel through pods to green seeds. Most seeds contain a single larva. (1) This species can spread with the movement of infested Mimosa nursery stock or through seeds in California. 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: Mimosa tree is a widely distributed ornamental tree and is cultivated in California. Bruchidius terrenus is considered a serious pest of Mimosa trees and can reduce seed production of the host plant significantly. Other Bruchidius species are known to reduce seed production in the host plant by as much as 80 % (2). In southern California, infection by Bruchidius terrenus may result in loss of markets. It receives a Low (1) 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: Bruchidius terrenus is not likely to lower biodiversity and disrupt natural communities. It is also not expected to affect threatened or endangered species. Since mimosa tree is cultivated in California for its shade, fragrant pompon-like flowers and fern-like compound leaves, infection by Bruchidius terrenus could trigger additional chemical treatment by growers. In desert areas, Mimosa tree makes a fine patio tree because of its light, filtered shade and umbrella form. If this tree were to get infested by Bruchidius terrenus, there could be impacts on home garden plantings in warmer and desert areas of California. It receives a Medium (2) in this category.

Evaluate the environmental impacts of the pest on California using the following criterion:

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:

– 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 Bruchidius terrenus (Seed beetle): Medium (10)

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: Bruchidia terrenus has been reported from Ukiah in Mendocino County in the fall of 2015 and again in 2016 during the same period. This indicates it might be establishing in that area.  It receives a Low (-1) in this category.

Evaluate the known distribution in California. Only official records of specimens 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:

Impacts of Bruchidius terrenus on mimosa trees in California is unknown. To date, there have been two reports of this beetle from the same area in Mendocino County. There have not been any detection surveys done in California for the presence of Bruchidius terrenus or other Bruchidius species. Since Mimosa trees are widely cultivated and naturalized in California, it is possible that this seed beetle could be affecting its host plants in other areas of California.

 Conclusion and Rating Justification:

Bruchidius terrenus is expected to have significant economic and environmental impacts to ornamental plantings of Mimosa trees growing areas in California. Based on all of the above evidence provided, a “B” rating is justified

References: 
  1. Hoebeke, Richard, Wheeler Jr., A.H, Kingsolver, John M and Stephan, David L 2009. First North American Records of the East Palearctic Seed Beetle Bruchidius terrenus (Coleoptera: Chrysomelidae: Bruchinae), A Specialist on Mimosa (Albizia julibrissin, Fabaceae). Florida Entomologist 92(3):434-440.
  2. Landry, Cynthia, 2011. National Pest Advisory Group Report: Bruchidius terrenus (Sharp): Seed Beetle http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.401.213&rep=rep1&type=pdf
  1. Redland Daily Facts: 06/24/2013: Mimosa is best-selling tree in Southern California. Accessed: 11/17/2016 http://www.redlandsdailyfacts.com/article/ZZ/20130624/NEWS/130629042
  1. Plant Invaders of Mid Atlantic Natural Area, National Park Services; US Fish and Wildlife Services: Silk Tree. Accessed: 11/17/2016 https://www.nps.gov/plants/ALIEn/pubs/midatlantic/alju.htm
  1. Missouri Botanical Gardens: Albizia julibrissin. Accessed:11/17/2016 http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=a848
  1. Los Angeles Arboretum Garden: Some outstanding shade trees of Southern California. Accessed: 11/17/2016 http://www.arboretum.org/some-outstanding-shade-trees-for-southern-california/
  1. Meyer, Rachelle. 2010. Albizia julibrissin. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Accessed: 11/18/2016. Available: http://www.fs.fed.us/database/feis/plants/tree/albjul/all.html
  1. Plant Maps: Interactive 2012 USDA Gardening and Plant Hardiness Zone map for California. Accessed: 11/18/2016 http://www.plantmaps.com/interactive-california-2012-usda-plant-zone-hardiness-map.php
  1. USDA Phytosanitary Certificate Issuance & Tracking System (PCIT) Phytosanitary Export Database (PExD). Accessed: 11/17/2016 https://pcit.aphis.usda.gov/pcit/
  1. Pest and Damage Record Database: Plant Health and Pest Prevention Services; California Department of Food and Agriculture, Accessed: 11/17/2016

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.


Comment Period:  CLOSED

1/11/2017 – 2/25/2017

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Pest Rating: B