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.

The tropical root weevil, Diaprepes abbreviatus (L.), has been a pest of citrus and ornamental plants since its introduction into Lake County, FL, in 1964. Since then, it has colonized the Florida peninsula to the south of its point of introduction but has not expanded its range to the north. A lower threshold for oviposition by D. abbreviatus was estimated as 14.9 degrees C. Eggs were highly susceptible to cold, with 95% mortality (LTime95) occurring in 4.2 d at 12 degrees C. Relative susceptibility of life stages to cold was eggs > pupae > larvae > adults. Archived weather data from Florida were examined to guide a mapping exercise using the lower developmental threshold for larvae (12 degrees C) and the lower threshold for oviposition (15 degrees C) as critical temperatures for mapping the distribution of D. abbreviatus and the potential for establishment of egg parasitoids. Probability maps using the last 10 yr of weather data examined the frequency of at least 10, 15, 20, 25, or 30 d per winter when soil temperature was <or=12 degrees C. The geographic area that experienced between 15 and 20 d per winter with mean daily soil temperature <or=12 degrees C closely approximated the northern limit of D. abbreviatus in Florida. Homologous maps of Arizona, California, and Texas predict the areas where soil temperatures favor establishment of D. abbreviatus. Successful establishment of egg parasitoids in Florida seems to be limited to southern Florida, where mean daily air temperatures fall below 15 degrees C <25 d/yr. By this measure, we predict that egg parasitoids will not establish in Arizona, California, or Texas.