Host-instar selection, interspecific competition, and reproductive capacity of extant and novel parasitoids (Hymenoptera: Braconidae) on Egyptian cotton leafworm

Abstract

Abstract Background Cotesia marginiventris (Cresson) and Microplitis rufiventris Kok. (Hymenoptera: Braconidae) are larval endoparasitoids of Spodoptera frugiperda (Smith) and S. littoralis (Boisd.), respectively. Cotesia marginiventris was introduced in Egypt to control the recent invasive pest, S. frugiperda and local one, S. littoralis. Therefore, competition between the two parasitoid species may occur. Results When single females of C. marginiventris (Exp. 1), single females of M. rufiventris (Exp. 2), and one female each of C. marginiventris and M. rufiventris (Exp. 3) were offered a choice of 60 1st, 60 2nd, and 60 3rd instars, of the tested host species, S. littoralis and different parasitization levels were obtained. In the non-competitive context (Exps. 1, 2), all instars were parasitized, but C. marginiventris and M. rufiventris parasitized primarily 2nd and 3rd instar host larvae, respectively. In the competitive context (Exp. 3), the same preference pattern emerged but the percentage of parasitism was lower than in each of the two non-competitive contexts. Conclusions M. rufiventris appears to be a superior competitor when simultaneously exploiting the host with the other parasitoid species. The knowledge of this work can be used to predict and/or understand possible outcomes of a biological control program using the two biocontrol agents against one or the two pests species, and to gain insight into possible biotic interference between species at the same trophic level exploiting the same host. Graphical abstract