ECOLOGY AND POPULATION BIOLOGY Sperm Precedence in Colorado Potato Beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae): Temporal Variation Assessed by Neutral Markers

Variation in sperm precedence was examined in the Colorado potato beetle, Leptinotarsa decemlineata Say, using neutral allozyme markers. Two temporal components were studied: (1) pairing duration and (2) time since initial pairing. We used two pairing protocols that differed in the timemales and femaleswere allowed tomate for Þrst and secondpairings.Whenpairingswere limited to 8 h each for the Þrst and second male, the proportion of offspring in the xth egg mass attributable to the second male, P2(x), rose from 68% in the Þrst egg mass after pairing with the second male to 78% in the tenth egg mass. When pairing was extended so that the Þrst male-female pair had time to produce three egg masses and the second male was allowed to remain with the female indeÞnitely, P2(x) rose from 44% in the Þrst eggmass after pairingwith the secondmale to nearly 100% in the third and subsequent egg masses. Observations that (1) multiple matings are necessary to Þll the femaleÕs spermatheca and (2) the last male accounts for a greater proportion of offspring with time, provide evidence for both the sperm mixing and sperm displacement hypotheses. These data also help to explainmale-guarding behavior inColorado potato beetle. Because the allozymemarkerswere shown to be neutral with respect to Þtness, other aspects of mating behavior could be tested by establishing a similar series of unique lines.