The soybean aphid, Aphis glycines, was discovered in the United States in the summer of 2000. Since that initial discovery the aphid has spread across northern soybean production regions. In 2001, we examined the photosynthetic responses of soybeans to low densities of aphids (less than 50 aphids per leaf). This examination included photosynthetic rates, leaf fluorescence responses, and photosynthetic responses to variable carbon dioxide and light levels. Additionally, biochemical analyses for chlorophyll content and stable carbon isotopes were used to differentiate potential differences in stomatal versus mesophyll limitations to photosynthesis. We observed rate reductions of up to 50% on infested leafs, including leaves showing no apparent symptoms of aphid injury (such as chlorosis). No differences in chlorophyll content were observed and fluorescence data indicated photoelectron transport was not impaired. These results indicate that substantial physiological impact on soybean is possible even at low densities. Also, the conventional view of aphid injury acting through reductions in chlorophyll content and light harvesting reactions of photosynthesis is not supported by our findings in this system.
Species 1: Homoptera Aphididae Aphis glycines (Soybean aphid)
Keywords: Photosynthesis, Non-photochemical quenching
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