|Oliver, Kerry - University Of Georgia|
|White, Jennifer - University Of Kentucky|
|Asplen, Mark - University Of Minnesota|
|Heimpel, George - University Of Minnesota|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2017
Publication Date: 5/31/2017
Citation: Hopper, K.R., Kuhn, K.L., Lanier, K., Rhoades, J.H., Oliver, K.M., White, J.A., Asplen, M.K., Heimpel, G.E. 2017. The defensive aphid symbiont Hamiltonella defensa affects host quality differently for Aphelinus glycinis versus Aphelinus atriplicis. Biological Control. doi:10.1016/j.biocontrol.2017.05.008.
Interpretive Summary: Aphids are major pests of many crops, and our laboratory studies different types of parasitic wasps for biological control of aphid pests. Aphid pests often harbor bacteria that may affect their ability to feed on a particular plant species or alter their resistance to parasitic wasps. The cowpea aphid is a pest of many crops that harbors a bacterium that may defend it against parasitic wasps. In laboratory experiments, we compared parasitism by two parasitic wasps species of cowpea aphids that were either infected with or cured of the bacterium. We found that infection by the bacterium had no effect on parasitism by the parasitic wasps and increased the numbers of adults and female size of the aphid. These findings support a hypothesis that the bacterium exhibits specific protective effects and may explain our previous findings on the patchy distribution of this aphid/bacterium interaction. It also means that the bacterium and perhaps other protective bacteria will not affect aphid biological control by some parasitic wasp species. These findings will be useful in managing pest aphids with biological control by parasitic wasps.
Technical Abstract: Endosymbiont interactions with hosts have important affects on fitness, including the fitness of many pest and beneficial species. Among these interactions, facultative endosymbiotic bacteria can protect aphid species from parasitoids. APHIS CRACCIVORA and ACYRTHOSIPHON PISUM harbor the symbiotic bacteria HAMILTONELLA DEFENSA and its bacteriophage APSE. Infection by H. DEFENSA defends these aphids against some but not all parasitoid species in the hymenopteran family Braconidae. Here, we report results showing that parasitism of aphids infected with H. DEFENSA/APSE by two APHELINUS species did not differ from that of uninfected aphids. The heavily chorionated eggs of APHELINUS may prevent passage of toxins from H. DEFENSA/APSE during parasitoid egg development and thus vitiate the protection of the aphid from parasitism. While APHELINUS ATRIPLICIS showed no difference in fitness components between infected and uninfected aphids, APHELINUS GLYCINIS actually produced more adult progeny and larger female progeny on infected than on uninfected aphids. Our results and reasoning suggest that Aphelinus species may be harmed by H. DEFENSA/APSE that effects eggs because all APHELINUS have anhydropic, heavily chorionated eggs, which will not absorb toxins during embryogenesis. More broadly, APHELINUS species may not be harmed by other secondary symbionts or their phages if the mechanism of defense involves toxins that affect eggs. Our results are good news for biological control using APHELINUS species.