1.13.5
BARLEY YELLOW DWARF VIRUS MODIFICATION OF HOST-PLANT CHOICE IN THE COMMON GREEN APHID SCHIZAPHIS GRAMINUM

AD STEWART and SE KELLEY

Department of Biology, Emory University, Atlanta, GA 30322, USA

Background and objectives
Plant appearance can influence aphid behaviour. Specifically, a previous study demonstrated that aviruliferous individuals of the common greenbug Schizaphis graminum significantly preferred grass tillers infected with barley yellow dwarf virus, strain SGV (BYDV-SGV), over uninfected tillers [1]. However, if aphids maintain this preference after BYDV acquisition, under most circumstances it will reduce virus spread. Therefore we ask whether BYDV acquisition alters aphid preference in favour of uninfected tillers.

Methods and materials
Pots of the common grass Anthoxanthum odoratum were separated into individual tillers and inoculated with either BYDV-SGV or mock-inoculated. Tillers were allowed to grow into large plants and then again divided into single tillers. Isolation chambers were constructed housing either infected or uninfected plants and aviruliferous aphids were added. Aphid feeding was allowed for 10 days. Both aviruliferous and viruliferous aphids taken from these chambers were then given a randomized series of choice trials. Each replicate of trials consisted of two control pots (both tillers BYDV-infected or both uninfected) and two experimental pots (one BYDV-SGV-infected tiller and one uninfected tiller) randomly selected from a pool of pots. Trials were conducted in small pots with two tillers placed 2.54 cm apart. Aphids were placed between the two tillers in an 'arena' and allowed to 'choose' a tiller by climbing onto it. Aphids that left the arena were repositioned and allowed to choose again.

Results and conclusions
27 uninfected aphids were tested for a total of 54 experimental choices. Aviruliferous aphids significantly preferred infected tillers over uninfected tillers (P<0.01), confirming Kelley's earlier study [1]. Furthermore, a total of 27 infected aphids were tested with 54 experimental choices. In contrast with previous results, viruliferous aphids significantly preferred uninfected over BYDV-SGV-infected tillers (P<0.001), indicating that BYDV alters aphid behaviour. Aphid behaviour appears to be altered in a manner that is adaptive for the plant viral pathogen. Whether such behaviour is adaptive for the aphid remains to be determined.

References
1. Kelley SE, 1994. Philosophical Transactions of the Royal Society of London, Series B 346, 295-302.