Sperm precedence in the Colorado potato beetle, Leptinotarsa decemlineata (Say), was investigated using phosphoglucomutase (Pgm) allozymes as genetic markers. Females were mated to two males carrying different Pgm alleles, and the proportion of offspring sired by each male was determined by cellulose acetate gel electrophoresis. Our results indicate that Pgm alleles in the Colorado potato beetle are inherited in the Mendelian fashion, and there is no change in sperm utilization over time. We were also able to confirm that sperm precedence in this insect is incomplete, with about 72% of the larvae fathered by males at the second mating. Possible implications of incomplete sperm precedence for insecticide resistance management are discussed. [Full Text]