Mating behaviour in Oncopeltus fasciatus: circadian rhythms of coupling, copulation duration and ‘rocking’ behaviour

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Abstract
Circadian rhythms are demonstrated in initiation and duration of copulation, and in ‘rocking’ by females during mating in the large milkweed bug, Oncopeltus fasciatus. In constant light or darkness there were no more than two or three recognizable cycles of any of these rhythms. In addition, light directly stimulated copulatory attempts, but did not influence their chance of success. Copulations were generally shorter during the early‐mid photophase and longer during the late photophase in LD 16:8, while initiations of copulation were fewest during the scotophase. The males were mainly responsible for these rhythms. It is suggested that the diurnal rhythm in copulation duration probably evolved as a consequence of the rhythms of flight activity and/or oviposition. Sperm from the late photophase matings typically displaced 90–100% of sperm from prior matings, while sperm from the shorter early photophase matings typically displaced less prior sperm. Peak rocking activity during mating occurred from 6 to 8 h after lights‐on in LD 16:8. Little rocking occurred during the late photophase, when the greatest percent of pairs are in copula. Feeding and drinking inhibited rocking activity, but the feeding rhythm did not drive the rocking rhythm. Rocking appears not to function in promoting termination of mating, positioning of the aedeagus, nor to mediate mechanical stimulation of egg production. Its function remains unknown.