Symbiotic relationships between animals and microorganisms are common in nature, yet the factors controlling the abundance and distributions of symbionts are mostly unknown. Aphids have an obligate association with the bacterium Buchnera aphidicola (the primary symbiont) that has been shown to contribute directly to aphid fitness. In addition, aphids sometimes harbor other vertically transmitted bacteria (secondary symbionts), for which few benefits of infection have been previously documented. We carried out experiments to determine the consequences of these facultative symbioses in Acyrthosiphon pisum (the pea aphid) for vulnerability of the aphid host to a hymenopteran parasitoid, Aphidius ervi, a major natural enemy in field populations. Our results show that, in a controlled genetic background, infection confers resistance to parasitoid attack by causing high mortality of developing parasitoid larvae. Compared with uninfected controls, experimentally infected aphids were as likely to be attacked by ovipositing parasitoids but less likely to support parasitoid development. This strong interaction between a symbiotic bacterium and a host natural enemy provides a mechanism for the persistence and spread of symbiotic bacteria.

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Facultative bacterial symbionts in aphids confer resistance to parasitic wasps

Natural enemies are important ecological and evolutionary forces, and heritable variation in resistance to enemies is a prerequisite for adaptive responses of populations. Such variation in resistance has been previously documented for pea aphids (Acyrthosiphon pisum) attacked by the parasitoid wasp Aphidius ervi. Although the variation was presumed to reflect genotypic differences among the aphids, another potential source of resistance to A. ervi is infection by the facultative bacterial symbiont Hamiltonella defensa. Here, we explored whether variation among symbiont isolates underlies variation among A. pisum clones in resistance to A. ervi. Although maternally transmitted, H. defensa is sometimes horizontally transferred in nature and can be experimentally established in clonal aphid lineages. We established five H. defensa isolates in a common A. pisum genetic background. All of the five isolates tested, including one originating from another aphid species, conferred resistance. Furthermore, isolates varied in levels of resistance conferred, ranging from 19% to nearly 100% resistance. In contrast, a single H. defensa isolate established in five different aphid clones conferred similar levels of resistance; that is, host genotype did not influence resistance level. These results indicate that symbiont-mediated resistance to parasitism is a general phenomenon in A. pisum and that, at least for the isolates and genotypes considered, it is the symbiont isolate that determines the level of resistance, not aphid genotype or any interaction between isolate and genotype. Thus, acquisition of a heritable symbiont appears to be a major mode of adaptation to natural enemy pressure in these insects.

https://www.pnas.org/content/pnas/102/36/12795.full.pdf

Variation in resistance to parasitism in aphids is due to symbionts not host genotype

Preface. 1. Introduction. 2. Feeding Behaviour and Food Quality. 3. Host Specificity and Speciation. 4. Size. 5. Resource Tracking: Mechanism - Cyclical Parthenogenesis. 6. Resource Tracking: Mechanism - Polyphenism. 7. Resource Tracking in Time. 8. Resource Tracking in Space. 9. Population Dynamics. 10. Community Structure and Species Diversity. 11. Epilogue. References. Index.

Aphid Ecology An optimization approach

Biology and management of rice insects.

The success of introducing natural enemies for biological control was found to be about 75% higher employing new parasite–host (predator–prey) associations than those based on long-evolved associations between parasites and hosts. The lack of evolved interspecific balance in new species associations appears to explain the higher success rate. New exploiter–victim associations expand opportunities for the biological control of both introduced and native pests and should be used as the preferred method in selecting biological control agents.

New approach for selecting biological control agents

Keys are given for the determination of the families, subfamilies, genera, and the 119 species of aphids known from Australia. The keys are supplemented by 192 figures. The genera of Australian aphids are described in detail and a reference to a recent revision of the genus and to a detailed description of each species is given where possible. A summary of the known host plant range and geographical distribution of each species is given. A few references to recent economic literature are given for those species regarded as pests.

VF Eastop

Papers

A taxonomic study of Australian Aphidoidea (Homoptera).