Seasonal Adult Emergence Patterns and Soil Larval Distribution ofDiaprepes abbreviatus(Coleoptera: Curculionidae) in Southern California

Abstract

Diaprepes root weevil, Diaprepes abbreviatus L., was first found in southern California in 2005 and has since spread to citrus groves in a small area of southern California. To develop pest management programs for this pest, its seasonal abundance and distribution of immature stages (including teneral adults) in the soil were investigated. The seasonal abundance of D. abbreviatus adults was monitored with modified Tedders traps. Emergence of D. abbreviatus adults from soil pupation chambers occurred throughout most of the year, and peak emergence occurred from July to October. However, there was no secondary annual peak emergence over the 4 yr of study in California as has been observed in Florida, suggesting diaprepes root weevil is univoltine in southern California's cooler climate. Annual emergence cycles mirrored patterns of air temperature rather than rainfall. Seasonal abundance and the impact of climate on range expansion of diaprepes root weevil are discussed. The effect of the number and arrangement of traps on the number of adult D. abbreviatus caught was also investigated, and we determined that they did not have an effect on adult D. abbreviatus trap catch data. Immature life stages in the soil occurred under the tree drip line within the top 30.5 cm of soil and horizontally up to 96.5 cm from the tree trunk. The majority were observed between 17.8 and 45.7 cm from the crown of the trees, which is in the area of Tedders trap placement.