Skip to main content
ARS Home » Northeast Area » Newark, Delaware » Beneficial Insects Introduction Research Unit » Research » Publications at this Location » Publication #298567
Title: Factors limiting the spread of the protective symbiont HAMILTONELLA DEFENSA in the aphid APHIS CRACCIVORA

Author
item DYKSTRA, HANNA - University Of Georgia
item WELDON, STEPHANIE - University Of Georgia
item WHITE, JENNIFER - University Of Kentucky
item Hopper, Keith
item HEIMPEL, GEORGE - University Of Minnesota
item ASPLEN, MARK - University Of Minnesota
item OLIVER, KERRY - University Of Georgia

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2014
Publication Date: 9/1/2014
Citation: Dykstra, H.R., Weldon, S.R., White, J.A., Hopper, K.R., Heimpel, G.E., Asplen, M.K., Oliver, K.M. 2014. Factors limiting the spread of the protective symbiont HAMILTONELLA DEFENSA in the aphid APHIS CRACCIVORA. Applied and Environmental Microbiology. 80: 5818-5827.

Interpretive Summary: Aphids which are major crop pests often harbor inside their cells bacteria that may affect aphid traits, like ability to feed on a particular plant species or resistance to parasitic wasps. Despite such benefits, these bacteria are commonly found at intermediate prevalence in field populations. The cowpea aphid, APHIS CRACCIVORA, is a pest of many crops that harbors a bacterium, HAMILTONELLA DEFENSA, which confers protection against some groups of parasitic wasps, yet the bacterium is found at intermediate prevalence in natural populations. To identify factors influencing the spread of the bacterium in cowpea aphid, we estimated transmission rates between parent and offspring and assayed fitness of individuals and changes in infection rate over time in population cages using experimental lines with to evaluate infection costs. We found no consistent reduction in fitness of infected aphids in assays of individuals, but did find decreased infection over time in population cages. Transmission rate between parent and offspring were high, but not perfect, in the laboratory. Failure of transmission and costs of infection likely limit the spread of the bacterium in cowpea aphid populations. Despite being collected years apart and in different regions, our aphid lines were infected with a nearly identical strain of bacterium. We confirmed the presence of the bacterium in cowpea aphid blood, where it can interact directly with parasitic wasps, which are used in biological control of aphids.

Technical Abstract: Many insects are associated with heritable facultative symbionts that mediate important ecological interactions, including host protection against natural enemies. Despite such benefits, facultative symbionts are commonly found at intermediate frequencies in surveyed populations. The cowpea aphid, APHIS CRACCIVORA, is a polyphagous crop pest that harbors the facultative symbiont HAMILTONELLA DEFENSA, which confers protection against some groups of parasitic wasps, yet H. DEFENSA is found at intermediate frequencies in natural populations. To identify factors influencing H. DEFENSA spread in AP. CRACCIVORA, we estimated vertical transmission rates and assayed fitness components of individuals and infection dynamics in population cages using experimental lines with controlled genetic backgrounds to evaluate infection costs. Similar to results with the pea aphid, ACYRTHOSIPHON PISUM, we found no consistent costs to infection using fitness component assays, but did find clear costs to infection in population cages. Maternal transmission rates in AP. CRACCIVORA were high, but not perfect, in the laboratory. Transmission failures and infection costs likely limit the spread of protective H. DEFENSA in AP. CRACCIVORA. Despite being collected many years apart and in different regions of North America, our experimental aphid lines were infected with a nearly identical strain of H. DEFENSA that carried a shiga-like toxin-encoding APSE4 bacteriophage. We confirmed the presence of H. DEFENSA in AP. CRACCIVORA hemolymph, where it can interact directly with endoparasites.