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Project description

Management of the citrus root weevil, Diaprepes abbreviatus (L.) (01XA003)
Program Exotic Pests and Diseases Research Program
Principal
investigators
E.E. Grafton-Cardwell, Entomology, UC Riverside
J.E. Pena, Tropical Research and Education Center, University of Florida
R.F. Luck, Entomology, UC Riverside
C.W. McCoy, Citrus Research and Education Center, University of Florida
K.E. Godfrey, CDFA, Biocontrol Program
Host/habitat Citrus
Pest Diaprepes Root Weevil Diaprepes abbreviatus
Discipline Entomology
Review
panel
Agricultural Systems
Start year (duration)  2001 (Two Years)
Objectives Investigate the use of Beauveria bassiana for the control of Diaprepes abbreviatus adults in citrus as a part of an integrated pest management program.

Evaluate the establishment potential and efficacy of egg parasitoids of Diaprepes abbreviatus for possible inclusion in an integrated pest management program.

Educate citrus growers in California about recognition and integrated management of Diaprepes abbreviatus.

Final report Diaprepes root weevil (formerly known as the citrus root weevil) is currently found in Florida and Texas and poses a threat to the citrus and nursery industries in California. Diaprepes larvae attack roots, and adults attack the foliage of many crops and ornamentals. Studies are currently under way in Florida to find environmentally sound control tactics to reduce the impact of the weevil both in Florida and in California, once the weevil arrives in that state. The first tactic being studied involves using a strain of a fungus that is highly specific to insects, Beauveria bassiana, to kill adult weevils. In studies conducted this year in Florida, a special trap called a "Tedders trap," has been shown to attract adult weevils. A strain of Beauveria bassiana (BotaniGuard), a fungal pathogen of adult root weevils, was applied to the surface of Tedders trap. Thus, the trap could be used as both a monitoring method and a method to distribute the fungus into the weevil population to control it biologically.

The second tactic studied in Florida involves the use of tiny, stingless wasps (parasites) that attack the egg stage of the weevil. Researchers released two species of parasites known as Quadrastichus haitiensis and Aprostoccetus vaquitarum in Diaprepes-infested citrus groves and ornamentals in 10 counties in southern and mid-Florida in 1999 and 2001. Approximately 1 million parasitoids were released across the state. Both wasps were recovered from citrus and ornamentals in 2002 and are now considered established in the southern portions of the state. The parasite A. vaquitarum appears to be more successful than Q. haitiensis, and it dispersed slowly from southern Florida toward north counties during 2002. In the counties where it has established, this tiny wasp causes 79 to 91% mortality to weevil eggs. Establishment and recovery of the parasitoids appears to be more successful in pristine habitats; ornamental plant nursuries than in citrus groves. It is likely that the pesticides that are applied to citrus for other pests are hindering the parasites. For instance, tests were conducted in 2002 to determine the effects of Imidan (phosmet), Acramite (bifenazate), Micromite (diflubenzuron), and oil on A. vaquitarum survival. Parasites survived Imidan, Acramite, and Micromite very well, but oil caused reduced parasitism because it causes the leaves to separate from the egg masses. A. vaquitarum does not lay eggs in exposed egg masses. New species of parasites that attack the weevil eggs, Fidiobia dominica and Haeckelianai sperata, 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.

In California, a number of meetings were conducted throughout the state to educate citrus growers, nurserymen, agricultural inspectors, regulators, and other interested individuals about the threat of Diaprepes root weevil to California agriculture. At each meeting, an educational booklet was distributed (Grafton-Cardwell, E. E., K. E. Godfrey, J. E. Pena, C. W. McCoy, and R. F. Luck. 2004. Diaprepes Root Weevil. UC ANR Publication 8131. 8 pp. http//anrcatalog.ucdavis.edu/pdf/8131.pdf). We provided dried specimens of adult Diaprepes root weevil, copies of the 8131 publication, and a PowerPoint slide show of the biology and monitoring methods to UCCE Extension offices and every agriculture commissioner's office in California. A Web site, http://citrusent.uckac.edu/Diaprepeshomepage.htm, hosted by the Kearney Ag Center was produced.

Second-year
progress
Diaprepes root weevil (formerly known as the citrus root weevil) is currently found in Florida and Texas and poses a threat to the citrus and nursery industries in California. Diaprepes larvae attack roots and adults attack the foliage of many crops and ornamentals. Studies are currently underway in Florida to find environmentally sound control tactics to reduce the impact of the weevil both in Florida and in California, once the weevil arrives in that state. The first tactic being studied involves using a strain of a fungus that is highly specific to insects, Beauveria bassiana, to kill adult weevils. In studies conducted this year in Florida, a special trap, called a "Tedders trap", has been shown to attract adult weevils. A strain of Beauveria bassiana (BotaniGuard), a fungal pathogen of adult root weevils was applied to the surface of the Tedders trap. Thus the trap could be used as both a monitoring method and a method to distribute the fungus into the weevil population to control it biologically.

The second tactic studied in Florida this past year involves the use of tiny, stingless wasps (parasites) that attack the egg stage of the weevil. Researchers began releases of two species of parasites known as Quadrastichus haitiensis and Aprostocetus vaquitarum in Diaprepes-infested citrus groves and ornamentals in ten counties in southern and mid Florida in 1999 and 2001, respectively. A total of 1,412,000 Q. haitiensis and 285,400 A. vaquitarum were released in 2002. Both wasps were recovered from citrus and ornamentals in 2002 but recovery was more successful from ornamentals than citrus. It is likely that the pesticides that are applied to citrus for other pests are hindering the parasites. Tests were conducted in 2002 to determine the effects of Imidan (phosmet), Acaramite (bifenazate), Micromite (diflubenzuron), and oil on A. vaquitarum survival. Parasites survived Imidan, Acramite, and Micromite very well, but oil caused reduced parasitism because it causes the leaves to separate from the egg masses. A. vaquitarum does not lay eggs in exposed egg masses.

In California, an effort is underway to educate citrus growers, nurserymen, and other interested individuals as to the threat of Diaprepes root weevil. An educational booklet and a web site hosted by the Kearney Ag Center were produced in 2002. The educational booklet was used at workshops conducted in California.

First-year
progress
Diaprepes root weevil (formerly known as the citrus root weevil) is currently found in Florida and Texas and poses a threat to the citrus and nursery industries in California. Studies are currently underway in Florida to find more environmentally sound control tactics to reduce the impact of the weevil both in Florida and in California, once it arrives. The first tactic being studied involves using a number of strains of a fungus that is highly specific to insects, Beauveria bassiana, to kill adult weevils. In studies conducted this year in Florida, a special trap, called a "Tedders trap", has been shown to attract adult weevils, and the number of adults found in a trap was related to the number of egg masses and first instar larvae found in the trapping area. This means that the trap can be used to attract most of the weevils within an area for contact with the fungus and as a monitoring tool within a grove. In addition, several virulent strains of the fungus have been identified for study.

The second tactic studied in Florida this past year involves the use of tiny, stingless wasps (parasites) that attack the egg stage of the weevil. Two species of parasites were released in infested groves in Florida, and in some release areas, recovered. In addition, studies were conducted to determine the best way to rear large numbers of parasites for release, determine the age of weevil egg that the parasite adult prefers for oviposition, and determine the age of the parasite adult at which most of the oviposition occurs.

In California, an effort is underway to educate citrus growers, nurserymen, and other interested individuals as to the threat of Diaprepes root weevil. An educational booklet and a web site are being produced. The educational booklet will be used at workshops that will be conducted in California later this year. The web site will be hosted by the Kearney Agricultural Center.

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