Acquisition and Transmission of Pea Enation Mosaic Virus by the Individual Pea Aphid

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Abstract
Pea enation mosaic virus (PEMV) was detected by enzyme-linked immunosorbent assay (ELISA) in individual nymphs or adults of A. pisum. The virus concentrations of an infective aphid may be below the level (5 ng/ml, based on 1 aphid homogenized in 0.2 ml of phosphate-buffered saline) that is detectable by ELISA. The amount ingested during a 24-h acquisition access period (AAP) varies widely among individual aphids, from a nondetectable level up to 40 ng/ml for nymphs and up to 200 ng/ml for adults. This variation reflects a highly uneven distribution of PEMV in the phloem cells of the source plant. The amount accumulated in the aphids during the AAP increases rapidly up to 16 h and then continues at a lower rate. Ingestion and excretion are approximately in equilibrium after 16 h and the subsequent lower rate of increase may be due to enlargement of the intestinal tract of the growing insect. Large amounts of virus were detected in the intestinal tract and small amounts in the hemolymph. Most of the virus passed through the intestinal tract within 6 days after acquisition when aphids were feeding on healthy plants [pea seedlings]. The infectivity of groups of aphids and their average viral charge were closely related. The transmission efficiency of individual aphids was poorly related to the amount of virus carried. The length of the latent period of an individual aphid was not closely related to either viral charge or transmission efficiency.