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 time males and females were allowed to mate for first and second pairings. When pairings were limited to 8 h each for the first and second male, the proportion of offspring in the xth egg mass attributable to the second male, P2(x), rose from 68% in the first egg mass after pairing with the second male to 78% in the tenth egg mass. When pairing was extended so that the first male-female pair had time to produce three egg masses and the second male was allowed to remain with the female indefinitely, P2(x) rose from 44% in the first egg mass after pairing with the second male to nearly 100% in the third and subsequent egg masses. Observations that (1) multiple matings are necessary to fill the female’s 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 explain male-guarding behavior in Colorado potato beetle. Because the allozyme markers were shown to be neutral with respect to fitness, other aspects of mating behavior could be tested by establishing a similar series of unique lines.
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Vol. 96 • No. 5