Aggressive encounters between males inChrysolina aurichalcea (Coleoptera: Chrysomelidae)

During the breeding season ofC. aurichalcea, an unpaired male is occasionally seen attacking a mating male on the host plant,Artemisia princeps. To clarify the significance of this behaviour, aggressive encounters between an unpaired male and a mating male were observed 269 times in experimental conditions. Intruders resulted in take-over (10.4%), loss (36.5%), draw (39.0%), or non-interference (14.1%). Frontal attack had 5 times higher probability of take-over than back one. A larger unpaired male had a slightly greater chance of take-over (P<0.02). The importance of aggressive encounters was discussed in view of sperm competition and of cost and benefit.