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



The team of researchers, led by entomologist Steve Lapointe at the ARS Subtropical Insects Research Unit 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 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 parasitoid insects that attack its eggs.



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. This explains why egg parasitoids of the weevil 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 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.