Diaprepes abbreviatus (Diaprepes Root Weevil)

California Pest Rating for

Diaprepes abbreviatus (Diaprepes Root Weevil)

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

On October 9, 2013, Nick Condos recommended that we run Diaprepes abbreviatus through our pest rating process to review its pest rating.

History & Status:

Background: Diaprepes root weevils are well documented as a serious pest of citrus that have been the subject of numerous research programs. This is reflected by more than 3,200 papers on Google Scholar. The adult weevils feed on the leaves of a wide variety of plants. They lay eggs in clusters of 30-265 between leaves. Larvae hatch from the eggs and drop into soil, where they feed on roots. They sometimes girdle structural roots or the root crown, leading to the death of plants. In addition, larval feeding provides infection sites for plant pathogens, especially Phytophthora spp². The weevil can spread to new areas as any life stage on nursery stock or as adult hitchhikers on landscaping equipment or similar conveyances.

Worldwide Distribution: Diaprepes abbreviatus is native to the Caribbean. It was accidentally introduced to Florida in 1964, presumably on nursery stock from Puerto Rico. The weevil has since spread over most of the southern and central portions of the state. It has more recently spread to Texas, Louisiana, and California, presumably via nursery stock.

Official Control: Diaprepes abbreviatus is not known to be under official control by any states or nations.

California Distribution: Diaprepes abbreviatus has established in coastal areas of San Diego, Orange, and southern Los Angeles County.

California Interceptions: Diaprepes abbreviatus have been found in nurseries and are sometimes intercepted on nursery stock from Florida and Puerto Rico.

The risk Diaprepes abbreviatus would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Cool winter temperatures are expected to limit the establishment of Diaprepes abbreviatus in California to most of San Diego and Imperial counties, eastern Riverside County, and coastal Orange and Los Angeles Counties¹. Dry soils are expected to further restrict where the weevil can establish within this endangered area³. Diaprepes abbreviatus receives a Low(1) in this category.

– 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: Diaprepes abbreviatus is highly polyphagous; it has been documented feeding on 270 plant species in 59 families⁴. The weevil receives a High(3) in this category.

– 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: Female Diaprepes abbreviatus have an extremely high reproductive potential, laying an average of 5,000 eggs⁴. The weevils are strong fliers but usually stay on the first host plant they encounter. They can move long distances on nursery stock. The weevil 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: The weevil is well documented as a serious pest that feeds on a wide variety of agricultural crops including Citrus, strawberries, avocado, peach, pear, and vegetables⁵. The weevil also feeds on a wide variety of ornamental plants that are popular in the nursery trade⁵. Larval feeding damages roots and creates infection sites for plant pathogens such as Phytophthora spp². Diaprepes abbreviatus is not expected to lower crop value; however, it can be expected to increase production costs at farms and nurseries as growers are advised to use pesticide drenches for larvae and foliar sprays for adults and eggs⁴. Citrus growers in Florida spend up to $400/acre for combined Diaprepes and Phytophthora control⁶. The weevil is not expected to trigger a loss of markets or significant changes to cultural practices. The weevil is not known to vector another pestiferous organism, but larval feeding on roots does facilitate infection by plant pathogens such as Phytophthora spp.. The weevil is not injurious or poisonous to animals and is not expected to affect water supply.

Although Diaprepes abbreviatus has not been documented to have a significant economic impact in coastal southern California, these areas are considered marginal for the establishment of the species¹. Inland conditions of Imperial County are expected to be significantly more favorable to the species due to warmer winter soil temperatures¹. Nevertheless, the presence of the root weevil has already triggered some new treatments in San Diego County as at least one grove manager is Rancho Santa Fe is treating citrus with Imidacloprid⁷. However, many growers in the area endangered by Diaprepes abbreviatus will already be treating with Imidacloprid to control Asian Citrus Psyllid, Diaphorina citri; they will therefore not be financially impacted by the weevil. However, the root weevils are not expected to be controlled by the foliar treatments used by organic growers. Additional chemical treatments can be expected in organic groves, increasing production costs. Diaprepes abbreviatus receives a Medium(2) in this category.

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

Economic Impact: B, E

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.

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: Environmental impacts of Diaprepes abbreviatus in California are likely to be limited by cold temperatures and dry weather. It is not expected to lower biodiversity, disrupt natural communities, or change ecosystem processes. Nor is it expected to directly affect threatened or endangered species or critical habitats. Residents of the infested areas in southern California have not been reporting weevils or damage, indicating that abbreviatus is not triggering new chemical treatments in the urban landscape. However, as it establishes in new areas the weevil is likely to trigger additional treatments by nurseries as they meet standards of cleanliness. It is also likely to trigger additional treatments in agricultural areas of San Diego, Riverside, and especially Imperial counties. In Florida, growers and nursery owners use pesticide drenches for larvae and foliar sprays for adults and eggs⁴. Diaprepes abbreviatus receives a Medium(2) in this category.

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

Environmental Impact: D

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:

Environmental Impact Score: 2

– 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 Diaprepes abbreviatus: Medium(11)**

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: Diaprepes abbreviatus has established a widespread distribution in coastal areas of southern California (San Diego, Orange, and Los Angeles Counties). However, it has not fully established in the endangered area, particularly the agricultural production areas of San Diego, Riverside, and especially Imperial counties. Diaprepes abbreviatus receives a Medium(-2) 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:

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

Uncertainty:

D. abbreviatus may negatively change agricultural cultural practices as growers might alter irrigation and fertilization practices to promote root growth in root weevil infested areas. Ants are believed to be major predators of Diaprepes root weevil larvae. It is possible that future ant control practices to facilitate establishment of the ACP parasitoid Tamarixia radiata will increase the damage caused by Diaprepes abbreviatus in Southern California. It is also possible that root-feeding by weevil larvae will help weaken citrus trees, making them more susceptible to HLB when it arrives in California, facilitating an epidemic of that disease in the state.

It is also possible that existing treatments for Asian citrus psyllid, Diaphorina citri, will help preclude the establishment of Diaprepes abbreviatus in citrus production. It is also possible that soil moisture in the agricultural production areas of San Diego, Imperial, and Riverside counties may be too low to sustain populations of Diaprepes abbreviatus.

Conclusion and Rating Justification:

Diaprepes abbreviatus has been established in southern California for seven years and has not spread beyond heavily irrigated coastal areas. However, Imperial County is expected to be much more favorable for the weevils due to higher winter soil temperatures. The weevil is likely to be managed by existing systemic treatments for Asian citrus psyllid in some conventional groves, but root feeding may increase the susceptibility of trees to pathogens such as Phytophthora spp.. The economic and environmental impacts of Diaprepes abbreviatus are likely to be limited to new chemical treatments and increased production costs in citrus groves, particularly in Imperial County. A ‘B’ rating is justified.

References:

¹Lapointe, S.L., D.M. Borchert, and D.G. Hall. 2007. Effect of Low Temperatures on Mortality and Oviposition in Conjunction With Climate Mapping to Predict Spread of the Root Weevil Diaprepes abbreviatus and Introduced Natural Enemies. Environmental Entomology 36(1):73-82. http://www.nappfast.org/pest%20reports/Diaprepes.pdf

²Lapointe, S.L. 2000. Thermal requirements for Development of Diaprepes abbreviatus (Coleoptera: Curculionidae). Environmental Entomology 29(2):150-156. http://www.crec.ifas.ufl.edu/extension/diaprepes/bibliography/PDF/EnvEnt292.pdf

³Lapointe, S.L. and J.P. Shapiro. 1999. Effect of soil moisture on development of Diaprepes abbreviatus (Coleoptera: Curculionidae). Florida Entomologist 82(2): 291-299. http://www.fcla.edu/FlaEnt/fe82p291.pdf

⁴Grafton-Cardwell, E.E., K.E. Godfrey, J.E. Pena, C.W. McCoy, and R.F. Luck. 2004. Diaprepes Root Weevil. University of California Division of Agriculture and Natural Resources Publication 8131. http://anrcatalog.ucdavis.edu/pdf/8131.pdf

⁵Knapp, J.L., S.E. Simpson, J.E. Pena, and H.N. Ngg. 2005. Diaprepes Root Weevil Host List. University of Florida ENY-641. http://edis.ifas.ufl.edu/pdffiles/IN/IN11900.pdf

⁶University of California-Riverside Center for Invasive Species Research website: http://cisr.ucr.edu/diaprepes_root_weevil.html

⁷Atkins, Robert and Tracy Ellis. Personal communications.

Responsible Party:

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

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