Mating patterns in the aphidophagous ladybird, Hippodamia variegata, depend on body size

Body size dependent mating patterns were investigated in an aphidophagous ladybird, Hippodamia variegata (Goeze), which was reared on mustard aphid, Lipaphis erysimi (Kalt.). Both males and females of varying body sizes were used to test the hypothesis that bigger is better. The costs of copulation on the life history traits of the mating partners were determined. Pairs of virgin beetles were allowed to mate once under controlled conditions and the duration of copulation of heavy beetles (504.00 ± 45.93 min) lasted significantly longer for than that of light beetles (270.00 ± 26.67 min). Body size was significantly positively correlated with duration of oviposition, fecundity and egg viability. When light individuals mated with heavy partners, copulation lasted longer between heavy males and light females (483.00 ± 54.73 min) than between light males and heavy females (378.20 ± 83.03 min). These results support the hypothesis that males determine the duration of copulation and that the reproductive success of large males is greater than that of small males. The longevity of heavy males was significantly shorter (37.40 ± 1.50 days) than that of light males (53.10 ± 2.84 days). This difference in the longevity of beetles of different sizes could contribute to the significant variation body size in H. variegata recorded both in the field and stock cultures, where light males outnumber heavy ones. Thus, although large males have a reproductive advantage over small males, other factors, such as reduced longevity, may constrain the evolution of even larger males.