Endosymbiotic Regiella insecticola reduce mummification in native and transinfected aphid hosts but do not prevent reproductive damage post parasitism

Abstract

Some bacterial endosymbionts of aphids can reduce mummification rates following attack by parasitoids, yet these endosymbionts can remain at a low frequency in populations even when parasitoids are present. The endosymbiont Regiella insecticola is uncommon in the major pest aphid Myzus persicae despite providing apparent protection against parasitoid attack. Here, we consider population-level effects associated with Regiella in its native M. persicae host as well as Regiella transinfected into pest Rhopalosiphum padi (oat aphids) and Diuraphis noxia (Russian wheat aphids), focusing on two parasitoids (Diaeretiella rapi, Aphidius colemani). We consider their impact not only on mummification rates but also on fecundity of non-mummified aphids that have been stung by wasps as detected by a qPCR assay to detect parasitoid DNA, with experiments simulating a single parasitoid attack event. Regiella produced a sharp decrease in mummification rates of their native and transinfected hosts, but aphids with Regiella that were stung (successful oviposition confirmed by molecular analysis) and not mummified showed low reproduction. The combination of these effects meant we did not detect major differences in the population size of infected and uninfected aphids. These results highlight the importance of considering multi-trait effects when assessing the impacts of endosymbiont infections and predicting the outcome of endosymbiont–host–parasitoid interactions.