Co‐occurrence of defensive traits in the potato aphid Macrosiphum euphorbiae

Abstract

1. Insecticide usage selects strongly for resistance in aphid populations, but this could entail fitness costs in other resistance traits. The potato aphid Macrosiphum euphorbiae Thomas exhibits intraspecific variation in susceptibility to parasitism by braconid wasps and provides a suitable species to study the relation between the defensive traits of parasitism and insecticide resistance. 2. Clonal lines (23 in total) of M. euphorbiae were established from aphids collected in 2013 from geographically separate populations in the U.K. Clonal lines belonged to five aphid genotypes, but one genotype predominated (78% of samples), and the facultative endosymbiont Hamiltonella defensa was detected in c. 40% of lines. 3. Total esterase activity in aphid tissues varied significantly between aphid genotypes and collection areas, but there was no clear pattern in relation to H. defensa infection or between collection sites likely to differ in insecticide pressures. 4. Five clonal lines representing low to moderate levels of enzyme activity, which included different aphid genotypes and presence/absence of H. defensa infection, were assayed for their susceptibility to the parasitoid wasp Aphidius ervi Haliday. Aphid mummification varied significantly between aphid genotypes, with low values in one genotype of aphids irrespective of H. defensa presence. 5. The results revealed that aphid lines belonging to the parasitism‐resistant genotype exhibited moderate levels of total esterase activity, indicating a competitve advantage for this genotype of M. euphorbiae when exposed to chemical and biological control factors in agroecosystems.

Learning‐induced switching costs in a parasitoid can maintain diversity of host aphid phenotypes although biocontrol is destabilized under abiotic stress

“…In aphids, including the cereal‐feeding species R. padi modelled in this study, effort has focussed on quantifying fitness costs to the aphid of parasitism resistance and not those experienced by the parasitoid. Fitness trade‐offs for aphids are often small or context dependent (Clarke et al, 2017; Clarke, Foster, Oliphant, Waters, & Karley, 2018; Leybourne et al, 2020) and not large enough to explain short‐term (days–weeks) changes in aphid phenotype frequency (Kwiatkowski & Vorburger, 2012; Smith et al, 2015); mechanisms other than aphid fitness costs, therefore, need to be invoked, such as those experienced by parasitoids. Fitness costs imposed by parasitoid oviposition behaviour might also explain why susceptible aphid types persist at moderate to high frequencies across aphid populations (Henry, Maiden, Ferrari, & Godfray, 2015; Zytynska & Weisser, 2016) and resistant aphids do not reach fixation despite appearing to be at a competitive advantage.…”

Untangling an insect virome from its endogenous viral elements

“…In terms of eukaryotes (Figure 1B), we found hits to Solanaceae, which includes the host plant species of M. euphorbiae, and Brachonidae parasitoid wasps (Insecta: Hymenoptera) in two samples (NT rPM>18,000). M. euphorbiae is known to be parasitized by hymenopterous wasps belonging to the superfamilies Ichneumonoidea (Braconidae) and Chalcidoidea [71]. In addition, there were some M. euphorbiae species-specific reads remaining, which did not map to the pea aphid reference genome but showed some homology to other aphid species (Insecta: Hemiptera).…”

Genomic insights into clonal diversity in UK populations of the Potato aphid,Macrosiphum euphorbiae

“…Common genotypes of M. euphorbiae demonstrate genotype-specific traits. For example, genotype 1 demonstrates innate resistance to parasitism by the hymenopterous parasitoid wasp Aphidius ervi (Clarke et al, 2017), and tends to exhibit moderate levels of esterase activity, which can contribute towards insecticide resistance (Clarke et al, 2018). Genotypes 1, 2 and 3 have been shown to differ in their ability to colonise wild and domesticated Solanum species, with genotype 2 faring better than genotypes 1 and 3 on the wild species S. berthaultii (Karley et al, 2018).…”

“…Potato aphid populations in the UK have been shown to comprise several genotypes, some of which show genotype-specific fitness traits (Clarke et al, 2016;Karley et al, 2017;Clarke et al, 2018). Those of specific interest include innate resistance to parasitism by the natural enemy Aphidius ervi (Clarke et al, 2017), where parasitism has a higher chance of failure in one aphid genotype (named genotype 1).…”

“…Studies of the pea aphid have detected aphid genotypic differences in A. ervi resistance (Li et al, 2002;Martinez et al, 2014), but the genetic basis is not known. If warming climate creates more favourable conditions for asexually reproducing aphids like M. euphorbiae, and as pesticides become less effective or even withdrawn (Plant Health Centre, 2021), it is increasingly important to understand the prevalence and persistence of aphid genotypes that might be resistant to biological (and chemical) control (Foster et al, 2002;Clarke et al, 2018).…”