[Pollinator] Invasive Weevils Spread to Southern California

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Invasive Weevils Spread to Southern California

October 25, 2005 — By University of California-Davis Statewide Integrated 
Pest Management Program 

DAVIS, Calif. — Entomologist Beth Grafton-Cardwell knew it was just a matter 
of time before the Diaprepes root weevil — a serious foe of citrus and nursery 
crops — showed up in California.

Grafton-Cardwell’s instincts were excellent because the destructive weevils 
that feed on more than 270 plant species were recently found in southern 
California. Until then, the pest was found only in Florida and Texas. It is native 
to the Caribbean region and was first found in Florida in 1964. Today, more 
than 30,000 acres of citrus in 23 counties in Florida are infested.

In September 2005, the root weevil was discovered in an urban area of Newport 
Beach, and a month later the pest surfaced 18 miles away in Long Beach. The 
weevil has been intercepted and destroyed numerous times in California in 
shipments of plants, truck trailers and cargo holds of aircraft. The California 
Department of Food and Agriculture (CDFA) is surveying these infestations in Los 
Angeles and Orange counties and developing an eradication plan. An emergency 
eradication response is necessary now to ensure the root weevil does not 
continue to multiply and spread to other areas of the state.

With 3-year funding from the Exotic/Invasive Pests and Diseases Research 
Program (EPDRP), Grafton-Cardwell, a researcher from University of 
California-Riverside, traveled to Florida in 2001 to work with researchers to find ways to 
prevent the spread of this insect to citrus groves and other crops in California.

“It’s imperative that we prevent this pest from migrating from urban areas 
into agricultural areas because the result could be devastating to California 
crops,” says Grafton-Cardwell.

The root weevil larvae plunge underground and feed on the roots of the plant. 
They will often encircle the taproot, impeding the ability of the plant to 
take up water and nutrients, killing the plant. This type of injury also 
provides an avenue for root rot infections. A single larva can kill young plants 
while several larvae can cause serious decline of older, established plants. 
Because larvae are below ground, it is difficult to detect them before decline of 
above ground portions of the host is observed.

In the Florida studies, researchers used a special trap called a “Tedders trap
” to collect adult weevils. This trap acts like a tree trunk, and the 
emerging beetle climbs up it and is caught in a container at the top. Researchers 
also applied a strain of a fungus to the surface of the Tedders trap to kill 
adult weevils. This way, the trap monitors the pest and also distributes the 
fungus into the weevil population to control it biologically.

In the Florida project, researchers also traveled to the Caribbean to collect 
tiny, stingless wasps (parasites) that attack the weevil’s eggs. Researchers 
released two parasites in groves and ornamentals that were infested with the 
pest in 10 counties in southern and central Florida in 1999 and 2001, 
respectively. Currently, the parasite — Aprostocetus vaquitarum — seems to have 
established well, however, it is sensitive to some insecticides.

Establishment and recovery of the wasps appears to be more successful in 
pristine habitats like ornamental plant nurseries than in citrus groves. It is 
likely that the pesticides that are applied to citrus for other pests are 
hindering the parasites.

New species of parasites that attack the weevil eggs were collected from 
islands in the Caribbean during 2002. These new species appear to be promising 
when tested under quarantine conditions, and permission from federal agencies to 
release these species in the field is pending.

Studies in Florida of natural enemies such as the fungi and parasites will 
help with California efforts to manage this pest.

Although a strong flyer, Diaprepes root weevils generally only fly up to 300 
yards to find food. The real threat of long distance spread of this pest could 
come from humans moving infested plants or soil.

Grafton-Cardwell is working with other agencies to educate citrus growers, 
nursery workers and others. Through funding from the EPDRP of the University of 
California Statewide Integrated Pest Management Program and Center for 
Invasive Species Research, a team of researchers from the CDFA, the University of 
California, and the University of Florida developed a brochure describing the 
biology of this pest and the management program used in Florida.

The booklet — Diaprepes Root Weevil, ANR Publication 8131 — is available for 
free online at http://anrcatalog.ucdavis.edu/pdf/8131, and the web site 
features the pest in relationship to citrus 
http://citrusent.uckac.edu/Diaprepeshomepage.htm. 

If you see this pest, call your local university extension office or 
agriculture commissioner.

Contact
Stephanie Klunk
Communications Specialist
(530) 754-6724
Statewide Integrated Pest Management Program
University of California-Davis
One Shields Avenue
Davis, CA 95616-8621
www.ipm.ucdavis.edu




Laurie Davies Adams
Executive Director
Coevolution Institute
423 Washington St. 5th
San Francisco, CA 94111
415 362 1137
www.coevolution.org
www.nappc.org

Our future flies on the wings of pollinators.
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