Bacteriophage effect on parasitism resistance

Abstract

Many studies have shown that the protection of the host Acyrthosiphon pisum (Hemiptera, Aphididae) against the parasitoid Aphidius ervi (Hymenoptera, Braconidae) is conferred by the interaction between the secondary endosymbiont Hamiltonella defensa and the bacteriophage APSE (Acyrthosiphon pisum secondary endosymbiont). This interaction consists of the production of toxins by the endosymbiont's molecular machinery, which is encoded by the inserted APSE genes. The toxins prevent the development of the parasitoid's egg, conferring protection for the host. However, the effects of this microscopic interaction on host-parasitoid dynamics are still an open question. We presented a new mathematical model based on the bacteriophage effect on parasitism resistance. We identified that the vertical transmission of the bacteriophage and the host survival after the parasitoid attack are potential drivers of coexistence. Also, we showed that the vertical transmission of H. defensa is proportional to the time that the protected population became extinct. Our results showed that the protected and unprotected hosts' survival after the parasitoid attack is fundamental to understanding the equilibrium of long host-parasitoid dynamics. Finally, we illustrated our model considering its parameters based on experiments performed with A. pisum biotypes Genista tinctoria and Medicago sativa.