Phenology of the Root Weevil Diaprepes abbreviatus In Lemon Groves In San Diego County, California

The root weevil, Diaprepes abbreviatus (L.) (Coleoptera:Circulionidae), a native of the Caribbean and a pest in Florida since 1964, was identified as a pest in southern California in 2005 and in San Diego County in 2006.  The phenology of the Diaprepes root weevil was examined in San Diego County California and compared with similar data reported from Florida.  Transects were set up in six hillside groves of rough lemons.  Four of the groves had been part of the CDFA eradication spray program, while two had not.  The 0.5 to 1.5 acre (0.2 to 0.6 ha) groves were on hillsides with heavy clay soil.  Although the groves differed in size, the transect setup was identical in the six groves.  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 comprising each transect.  Traps were checked weekly or biweekly from March 2008 through December 2009.  The number of adult weevils which emerged from the soil and collected in the Tedders traps reflected seasonal activity and abundance of Diaprepes. 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.