Potato aphid Macrosiphum euphorbiae performance is determined by aphid genotype and not mycorrhizal fungi or water availability

Abstract

Intra-and interspecific variation in plant and insect traits can alter the strength and direction of insect-plant interactions, with outcomes modified by soil biotic and abiotic conditions. We used the potato aphid (Macrosiphum euphorbiae Thomas) feeding on cultivated Solanum tuberosum and wild Solanum berthaulti to study the impact of water availability and plant mutualistic arbuscular mycorrhizal (AM) fungi on aphid performance and susceptibility to a parasitoid wasp (Aphidius ervi Haliday). Plants were grown under glass with live or sterile AM fungal spores and supplied with sufficient or reduced water supply. Plants were infested with 1 of 3 genotypes of M. euphorbiae or maintained as aphidfree controls; aphid abundance was scored after 1 week, after which aphid susceptibility to A. ervi was assayed ex planta. Solanum tuberosum accumulated c. 20% more dry mass than S. berthaultii, and root mass of S. berthaultii was smallest under reduced water supply in the presence of AM fungi. Aphid abundance was lowest on S. berthaultii and highest for genotype "2" aphids; genotype "1" aphid density was particularly reduced on S. berthaultii. Aphid genotype "1" exhibited low susceptibility to parasitism and was attacked less frequently than the other two more susceptible aphid genotypes. Neither AM fungi nor water availability affected insect performance. Our study suggests a fitness trade-off in M. euphorbiae between parasitism resistance and aphid performance on poor quality Solanum hosts that warrants further exploration, and indicates the importance of accounting for genotype identity in determining the outcome of multitrophic interactions.

The price of protection: a defensive endosymbiont impairs nymph growth in the bird cherry‐oat aphid, Rhopalosiphum padi

“…Intraspecific variation in R. padi mass gain in the present study was attributed mainly to aphid genotype and not to H. defensa infection (Fig. B), with individuals belonging to genotype E generally performing poorly compared with genotypes A and B. Aphid genotype is often identified as a key determinant of aphid performance, for example in S. avenae (Figueroa et al ., ) and M. euphorbiae (Karley et al ., ). A recent study reported that M. euphorbiae genotypes capable of forming endosymbiotic associations with H. defensa had higher fitness than those genotypes which did not support H. defensa infection, at least when feeding on a susceptible host plant species (Clarke et al ., ), which contrasts with the findings for R. padi lines assessed in the current study.…”

“…A recent study reported that M. euphorbiae genotypes capable of forming endosymbiotic associations with H. defensa had higher fitness than those genotypes which did not support H. defensa infection, at least when feeding on a susceptible host plant species (Clarke et al ., ), which contrasts with the findings for R. padi lines assessed in the current study. Differential effects of aphid genotype on fitness might also depend, however, on plant suitability for aphids (Karley et al ., ). In general, all R. padi genotypes examined in the present study performed poorly on the wild species HsP5 compared with the commercial barley cultivar Concerto, indicating that HsP5 is partially resistant to aphids irrespective of aphid genetic variation.…”

Plant and insect genetic variation mediate the impact of arbuscular mycorrhizal fungi on a natural plant–herbivore interaction

“…This method has been used extensively and consistently results in mycorrhizal colonisation of plant roots (e.g. Bennett et al, 2016;Karley et al, 2017). Notably, soil sterilisation removes most soil organisms, and the addition of AM fungal inocula adds both AM fungi and microbes associated with or co-extracted with the AM fungi.…”

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

“…Insecticide‐resistant M. persicae clones are thought to survive poorly at low temperatures (Foster et al, ), and perform less well than susceptible M. persicae clones on favourable host plant species (Silva et al, ). A recent study suggested that a parasitism‐resistant line of M. euphorbiae performed less well than susceptible lines on unfavourable Solanum hosts (Karley et al, ), which might cause poor persistence of the resistant genotype in diverse vegetation. This study highlights the importance of understanding the different selection pressures imposed by aphid parasitoids and insecticides, and the effects on aphid behaviour, performance and genotype persistence, which could alter the efficacy of biological and chemical controls in agroecosystems.…”