Lethal male–male combat in the parasitoid Melittobia acasta: are size and competitive environment important?

Interactions between organisms can lie anywhere along the spectrum from fatal conflict to total cooperation. To understand this variation, knowledge of the strategies that individuals use to acquire their resources is required. We tested theoretical predictions relating to conflict behaviour in a species of parasitoid wasp, Melittobia acasta, in which males compete for mates in their closed, natal patches. They engage in lethal combat to gain access to the females developing in their host. Environmental factors and individual traits both influenced conflict behaviour and contest outcome: fighting behaviour increased with the density of competitors and larger contestants were more successful. Our results also indicate that opponent assessment did not influence conflict behaviour and contests were always resolved by fighting.