We investigated the mating system and population genetic structure of the invasive haplodiploid palm-seed borer Coccotrypes dactyliperda in California. We focused on whether these primarily inbreeding beetles have a 'mixed-breeding' system that includes occasional outbreeding, and whether local inbreeding coefficients (F(IS)) varied with dominant environmental factors. We also analysed the genetic structure of C. dactyliperda populations across local and regional scales. Based on the analysis of genetic variation at seven microsatellite loci in 1034 individual beetles from 59 populations, we found both high rates of inbreeding and plentiful evidence of mixed-breeding. F(IS) ranged from -0.56 to 0.90, the highest variability reported within any animal species. There was a negative correlation between F(IS) and latitude, suggesting that some latitude-associated factor affecting mating decisions influenced inbreeding rates. Multiple regressions suggested that precipitation, but not temperature, may be an important correlate. Finally, we found highly significant genetic differentiation among sites, even over short geographic distances (< 1000 m).