Intraspecific competition and performance of Anagrus virlai parasitizing the corn leafhopper

Abstract

Intraspecific competition and avoidance of superparasitism are critical for biological control. In this study, we conducted behavioural and biological trials to assess intraspecific competition in the egg parasitoid Anagrus virlai, targeting the corn leafhopper Dalbulus maidis. Firstly, we investigated whether A. virlai can distinguish between unparasitized and parasitized host eggs using long-range cues in an olfactometer experiment. Secondly, we evaluated whether A. virlai parasitism and emergence under varying host densities are affected by the presence of multiple conspecific wasps foraging within the same host patch. In the olfactometer test, A. virlai did not differentiate between corn leaves with parasitized and unparasitized eggs. Regarding the parasitoid's performance, the number and percentage of parasitized eggs were influenced by the density of females foraging simultaneously in the same host patch. Significant increases in collective parasitism were observed when two or more parasitoids were present in each arena. Competitive interaction did not affect wasp emergence, and A. virlai proved to be a solitary species. Moreover, the negative relationship between per-capita parasitism and the number of conspecific wasps per arena demonstrated mutual interference among parasitoids. These findings highlight the impact of competitive interactions on A. virlai performance and suggest a potential aggregated response of the parasitoid to high-density patches of hosts.