Maps Predict Path of Destructive Citrus Pest

The distribution of diaprepes root weevils (Diaprepes abbreviatus) is constrained by temperature, a key finding that could be vital to predicting and limiting the spread of this pest, according to Agricultural Research Service (ARS) scientists in Ft. Pierce, Fla.

The team of researchers, led by entomologist Steve Lapointe at the ARS Subtropical Insects Research Unit (SIRU) in Fort Pierce, used probability maps to make the discovery.

Since its arrival in 1964, the diaprepes root weevil has been a major contributor to the decline of Florida's citrus industry. The pest's ability to feed on more than 200 host plant species has aided its spread throughout citrus-producing areas of peninsular Florida—the southern two-thirds of the state.

The probability maps use a combination of soil and air temperatures to delineate the current distribution of both the diaprepes root weevil and of parasitoid insects that attack its eggs and have potential to serve as biological controls of the pest.

The researchers have shown that adult female weevils stop producing eggs at 59 degrees Fahrenheit, and the eggs themselves are highly susceptible to cold. Eggs already laid become nonviable when exposed to 53 degrees F for 4.2 days—about 100 hours. This explains why egg parasitoids of D. abbreviatus haven't been able to establish themselves in northern Florida.

Using this knowledge, Lapointe and his team worked with scientists from the Animal and Plant Health Inspection Service's Center for Plant Health Science and Technology to develop probability maps to describe the current diaprepes distribution in Florida and in portions of Texas, Arizona and California that are most susceptible to its establishment. The maps will be used to guide survey and control efforts in those states.

Already, the parasites Quadrastichus haitiensis from Puerto Rico and Aprostocetus vaquitarum from the Dominican Republic—both introduced into southern Florida to control the weevil—are considered to be successfully established there.

Read more about the research in the May/June 2007 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief in-house scientific research agency.