Seasonal occurrence of Diaprepes abbreviatus (L.) in southern California

Diaprepes abbreviatus (L.) (Coleoptera: Curculionidae), a native of the Caribbean and a pest in Florida since 1964, invaded and established in southern California in 2005. The phenology of the Diaprepes root weevil was examined under the environmental conditions and soils found in southern California and compared with similar data reported from Florida. Adult trapping transects were placed in six citrus groves, four treated and two untreated. Each transect consisted of ten contiguous trees arranged in a diagonal line across each grove from northwest to southeast. Emergence of adult weevils was monitored using modified Tedders traps placed approximately 2ft (0.6 m) from the trunk of each tree in the transect. The number of emerging adult weevils was collected weekly or biweekly from March 2008 through December 2009. Patterns of Diaprepes adult emergence varied seasonally with changes in soil moisture and temperature in both California and Florida. In both wet and dry years, California weevil populations show only one seasonal emergence peak in late summer or fall, (July-November), unlike the two peaks reported in some weevil populations in Florida. Southern California winters are colder than those of weevil infested areas in Florida and southern California summers are much drier. Year-to-year differences in weevil densities appear to reflect differences in humidity and soil moisture. Statistically, more weevils showed up in the previously treated groves, which had older infestations than in the untreated, more recently infested groves.