Abstract
Bacterial endosymbionts have enabled aphids to adapt to a range of stressors, but their effects in many aphid species remain to be established. The bird cherry‐oat aphid, Rhopalosiphum padi (Linnaeus), is an important pest of cereals worldwide and has been reported to form symbiotic associations with Serratia symbiotica and Sitobion miscanthi L‐type symbiont endobacteria, although the resulting aphid phenotype has not been described. This study presents the first report of R. padi infection with the facultative bacterial endosymbiont Hamiltonella defensa. Individuals of R. padi were sampled from populations in Eastern Scotland, UK, and shown to represent seven R. padi genotypes based on the size of polymorphic microsatellite markers; two of these genotypes harbored H. defensa. In parasitism assays, survival of H. defensa‐infected nymphs following attack by the parasitoid wasp Aphidius colemani (Viereck) was 5 fold higher than for uninfected nymphs. Aphid genotype was a major determinant of aphid performance on two Hordeum species, a modern cultivar of barley H. vulgare and a wild relative H. spontaneum, although aphids infected with H. defensa showed 16% lower nymph mass gain on the partially resistant wild relative compared with uninfected individuals. These findings suggest that deploying resistance traits in barley will favor the fittest R. padi genotypes, but symbiont‐infected individuals will be favored when parasitoids are abundant, although these aphids will not achieve optimal performance on a poor quality host plant.
Highlights
Aphids form a diverse range of associations with endosymbiotic bacteria, ranging from obligatory to facultative and beneficial to parasitic
Aphid genotype was a major determinant of aphid performance on two Hordeum species, a modern cultivar of barley H. vulgare and a wild relative H. spontaneum, aphids infected with H. defensa showed 16% lower nymph mass gain on the partially resistant wild relative compared with uninfected individuals
Insect Science published by John Wiley & Sons Australia, Ltd on behalf of Institute of Zoology, Chinese Academy of Sciences, 27, 69–85
Summary
Aphids form a diverse range of associations with endosymbiotic bacteria, ranging from obligatory to facultative and beneficial to parasitic. Aphid species, including cosymbiosis with Wolbachia sp. In the banana aphid, Pentalonia nigronervosa (Coquerel) (De Clerck et al, 2015), and Serratia symbiotica in Cinara species (Meseguer et al, 2017). The most frequently detected facultative endosymbionts of aphids are Hamiltonella defensa, Regiella insecticola, S. symbiotica, Rickettsia sp., Ricketsiella sp., Spiroplasma sp., the Pea Aphid X-type Symbiont (PAXS) and Wolbachia sp. A concise review of endosymbiont occurrence in aphid populations (Zytynska & Weisser, 2016) found that the facultative endosymbionts S. symbiotica and Wolbachia infected the highest proportion of the aphid species assessed (47% and 43%, respectively).
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