Abstract and Summary

Available information suggests that male alfalfa butterflies (Colias eurytheme) make a nutrient investment during copulation. Sexual selection theory predicts that females, to maximize the material they receive, should preferentially mate with large, young, persistent males. In addition, males, to maximize the return on their investment, are predicted to mate preferentially with large females. To test these predictions, observations were made on interactions between lab-reared virgin females and males flying in the field. About half of all interactions ended in copulation. Analysis of the interactions revealed that: 1) young (fresh) males are more successful in courtship than old (worn) males, 2) males accepted by females are significantly less variable in size than males rejected by females, 3) persistence increases, up to a point, a male's chances of attaining copulation, and 4) the size of females accepted by males is less variable than that of rejected females. These results support the predictions in part but leave unanswered questions about why exceptionally large conspecific individuals are unattractive to members of both sexes.


Die Interaktionen noch unbesamter Weibchen von Colias eurytheme mit umherfliegenden Männchen lassen vermuten, daß beide Geschlechter in der “Balz”-Phase eine Partnerwahl treffen. Weibchen paaren sich bevorzugt mit frischgeschlüpften Männchen mittlerer Größe, die das fliegende Weibchen 7–10 s lang oder das sitzende Weibchen 4–5 s lang umbalzen. Diese Alters-und Größenbevorzugung zeigt sich auch an verpaarten — im Gegensatz zu einzeln gefangenen — Männchen. Männchen bevorzugen mittelgroße Weibchen.