SummaryThe sterile insect technique (SIT) is increasingly used to control pest insect populations. The success of SIT control programs depends on the ability to release sterile males and on the capacity of sterile males to compete with wild males to inseminate wild females. In this study, we evaluated the mating performance of Schistocerca gregaria (Försk.) males irradiated with 4 Gray. We compared reproductive traits, such as duration of precopulation time, mating duration, quantity of sperm stored by females after copulation, number of females mated successively and postmating competition of irradiated males with non-irradiated males. Irradiated males were able to mate but the resulting number of offspring was dramatically reduced compared to the average number of offspring observed during a regular mating. During a single copulation, irradiated males transferred fewer sperm than regular males but, theoretically, this quantity is enough to fertilize all the eggs produced by a female during its reproductive life. Irradiated males also had the ability to remove sperm from a previous mating with unirraditated males. This new information on the mating strategies helps explain the post-copulation guarding behaviour of S. gregaria.

The multiple mating by female (polyandry) is a widespread behavior in insect species. This behavior is known to be a kind of itness maximization, but some case of sexual selection factors can explain the evolution of this behavior in relation with the phenotype plasticity model. In this paper, we analyze the role of polyandry in the reproductive success and in the phase shift process in the gregarious desert locust. In an applied perspective, knowledge on the reproductive success and in the phase shift process is essential to perform mass rearing for human food production. Our results suggest that multiple mating is not associated with itness beneits. Polyandry acts as a signal of phase shift through ofspring. We showed that hatchlings of gregarious females mated only once are smaller and green at 87.2% in irst egg pods and produced the solitary form of the desert locust. The coloration of ofspring in females mated with two males reaches only 15.2% of green forms versus 84.8% of mostly blacks. In this study, we showed that females mated more than two times with diferent males produce larger eggs, heavier, and black hatchlings characteristic of gregarious phase known in S. gregaria.

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