Is there a link between potato aphid (Macrosiphum euphorbiae) protective endosymbionts and genotypes with the success of parasitoids used as biological controls in strawberry crops?

Abstract: The potato aphid (Macrosiphum euphorbiae) is an economically important pest of
strawberry crops. Current control of this pest relies on biological control, through releases of
the parasitoid wasp, Aphidius ervi. The recent description of resistance to this parasitic wasp in some populations of M. euphorbiae could indicate a reduction in the effectiveness of this
biological control. Resistance of aphids to parasitoids has been linked to aphid genotype and
endosymbiotic infections, but most of the research on this topic has been done under laboratory conditions, which oversimplifies the complexity of the factors involved in interactions between these species. Here, we test under field conditions whether the endosymbiont communities or genotypes of M. euphorbiae have a protective effect on their hosts and whether aphid diversity in the field is linked to parasitoid community diversity. To achieve this, we monitored four open polytunnels at a strawberry farm located in Staffordshire, UK, from March to November 2023 over one cropping season. We found a high diversity of aphid genotypes, with five present throughout the season. Single and multiple secondary bacteria were found with a noticeable increase in the frequency of infection with Regiella insecticola at the end of the season. The parasitoid community was dominated by Aphidius ervi and Praon volucre. Data analysis showed an interaction between the more abundant genotypes and parasitism pressure, showing that potato aphid parasitism is linked to its genotype and not secondary endosymbiont infections. No correlation between diversity indexes was found between potato aphid genotypes, secondary endosymbionts, and parasitoid communities, showing that a fluctuation in the intraspecific diversity of potato aphids does not translate into a fluctuation in the diversity of their main natural enemies. Together, this information informs on the likely effect of endosymbionts and genotypes on the effectiveness of biological control programmes based on parasitic wasps for control of M. euphorbiae in strawberry crops.