The detrimental effect of aphid feeding on plant growth has been reported from various crops around the world (Atakan and Ozgur, 1996; Hille Ris Lambert, 1970; Kimmins, 1986; Lowe, 1967; Miles, 1987). We first studied the effects of aphid feeding on cotton and dry matter production in 1999/2000. Prolonged feeding by heavy aphid populations significantly decreased cotton and dry matter production and raised questions about how aphids caused these effects. Contamination of leaves by honeydew, salivary effects and assimilate removal could all be factors. We also noticed that aphid infested plants often grew poorly, even before the level of honeydew production was very high, and speculated that perhaps aphids also affected the photosynthetic rate of cotton. Since it is known that the removal of leaf sugars (such as occurs during aphid feeding) can increase the concentration of sugars in the leaf and thereby give negative feedback to photosynthesis (Blechschmidt-Schneider, et al., 1989; Franck, et al., 2006), we decided to consider this factor first. Our subsequent work investigated any relationships between aphid populations and plant photosynthetic response; how many aphids would be required to elicit a response; and the duration of the response to become measurable.