Key to aphid tolerance

[BIOHEAD]

Dear Owen:
If I might be allowed to speculate on aphid susceptibility:

 Aphids carry diseases to which the arctic ecotype might be 
  vulnerable. Plant viruses are transmitted by aphids.

 There might be mechanical features of the vulnerable ecotype, not
  shared by heartier varieties. Stem cross sections might reveal
  protective fibrous bundle sheaths around the veins of resistant
  ecotypes.

 Resistant ecotypes might be hairier (more trichomes, especially
  glandular ones), thus impeding aphid mobility.

 Resistant ecotypes might be better able to form callose slime plugs,
  thereby limiting resource loss to the aphids. Vulnerable ecotypes
  in contrast might freely bleed phloem contents through punctured
  sieve tube members.

These are things I would look for. It is uncommon for aphids to actually
KILL plants. I have seen horribly thick infestations on wild and domestic
plants (Lupines, and roses), but cannot recall having an entire plant
die from the abuse.
                              Best,    George Ellmore
                                       Biology
                                       Tufts Univ.
                                       Medford, MA  USA