Short-term effects of two aphid species on plant growth and root respiration of three leguminous species

The short-term effects of cowpea aphids ( Aphis craccivora Koch) and pea aphids ( Acyrthosiphon pisum Harris), both Homoptera: Aphididae, on plant growth and respiration of excised, intact roots of cowpea [ Vigna unguiculata (L.) Walp. cv. Caloona], broadbean ( Vicia faba L. cv. Aquadulce) and garden pea ( Pisum sativum L. cv. Victory Freezer) seedlings were investigated, but not all plant-aphid combinations were used. Plant and root mean relative growth rates were significantly reduced within 10 days in the infested plants. Rates of total root respiration were was also significantly reduced in all infested plants within 10 days, presumably because of the reduced availability of translocate to the roots. The contribution of the cytochrome pathway to root respiration was significantly greater in control than in infested plants. The activity and engagement of the alternative respiratory pathway was also greater in control plants, and was absent in infested plants after 10 days infestation in all cases but one. These data indicate that the roots of aphid-infested plants were more efficient, in terms of energy conversion, than their respective controls.