Susceptibility of plants to aphids

[Owen Atkin]

In a recent study comparing the growth rates, biomass partitioning and 
respiration rates of alpine and high arctic ecotypes of Oxyria digyna,
our lab noticed that only the arctic ecotypes were susceptible to 
aphid infestation.  Quite by accident, some plants that had been left
unattended over the Christmas break became infested with a large number
of aphids.  The results was that the arctic ecotypes (3 different ones 
collected from Ellesmere Island at 80oN) were completely killed by the 
aphids.  In contrast, the 2 alpine ecotypes (Swiss and Canadian Rockies)
were almost totally unaffected. 

Our group has little knowledge of what attracts aphids to particular plants.
We would be very interested in any suggestions other parties might have on
why the alpine/arctic ecotypes differ so much in their tolerance of aphids.

Some background information:
All plants were grown hydroponically under 24 hour light at 20C
No difference in RGR was observed between the ecotypes
However, the alpines committed more resources to their leaves at the 
expense of the the stems and had thinner, more dense leaves (ie a greater
leaf weight ratio, specific leaf area and leaf dry matter content, but lower
leaf fresh weight to leaf area ratio [thinner leaves]) than did the arctic
ecotypes.

Any suggestions on the cause of the difference in aphid tolerance would 
be greatly appreciated. 

Owen Atkin, Dept of Botany, University of Toronto, Canada
oatkin at credit.erin.utoronto.ca