Mechanisms for inbreeding avoidance should be prevalent in insects that reproduce by arrhenotokous haplodiploidy because of the high potential production of unviable diploid males in inbred mating. It is particularly the case of aphid parasitoids that are usually considered as quasi-gregarious with a high level of local mate competition between sibs. Moreover, in some species, such as Aphidius matricariae, it seems that there is no recognition between related individuals and a sister brought into the presence of his brother generally accepted mating. Therefore, our hypothesis is that there is a series of mechanisms that minimize the encounter between two related individuals emerging from the same colony of aphids and that aphid parasitoid therefore are not actually semi-gregarious.

In that context, we have studied the steps preceding mating from the egg laying by a female in a colony of aphids until the emergence of her daughters and sons to analyse their mating probability. It appears that first, when attacking a colony, the mother female causes the dispersal of a part of parasitized or not parasitized aphids and that these aphids move then to different places of the plant or on nearby plants where they resettle. Secondly, the male development time is significantly shorter than that of females and their emergence pattern is different. Finally, in most cases, from the emergence, male and female parasitoids quickly leave the aphid colony in search of another colony before searching for a mate. The combination of these three mechanisms gives an extremely low probability of a sib mating. In this way, the costs associated with risk of inbreeding in these haplodiploid parasitoids are very small while avoiding the necessity of related recognition process.