Insect-Plant Interactions: Greenbugs (Homoptera: Aphididae) Disrupt Acclimation of Winter Wheat to Drought Stress

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Abstract
This growth-chamber study was designed to investigate the effect of greenbug, Schizaphis graminum (Rondani), feeding on physiological responses of wheat, Triticum aestivum L., associated with drought stress, to determine how drought stress affects greenbug density, and to determine how drought- and greenbug-resistant cultivars alter responses. The cultivars chosen were ‘Amigo’ (relatively resistant to biotype C greenbugs), ‘Sturdy’ (comparatively drought and greenbug susceptible), and ‘TAM W-101’ (comparatively drought resistant and greenbug susceptible). Greenbugs altered two potentially adaptive responses of wheat to drought; they virtually negated an increase in cell membrane stability associated with wheat conditioned to drought stress, and solute potential was reduced less in greenbug plus drought stress treatments than in drought stress-only treatments; water potential, however, was not altered by greenbug infestations. The lowered turgor pressure that resulted for infested plants suggests that osmotic adjustment (the maintenance of turgor through the accumulation of solutes in plants under drought stress) was also reduced by greenbugs. In addition, greenbug density (number of greenbugs per mg shoot dry weight) was greater on drought-stressed plants. These data provide physical and physiological evidence supporting field observations that greenbug infestations are potentially more damaging when wheat is subjected to drought than when rainfall is sufficient.