Biological and Transmission Characteristics of Acyrthosiphon pisum1 Biotypes Efficient and Inefficient as Vectors of Pea Enation Mosaic Virus2

Abstract

Seventeen colonies of the pea aphid, Acyrthosiphon pisum (Harris), were established from various areas of Michigan and compared, as vectors of the California (CALIF) and New York (NY) strains of pea enation mosaic virus (PEMV), with a pea aphid biotype (WARF) known to be a very inefficient vector of PEMV. The most efficient vector colony (hereafter: Biotype EL) transmitted CALIF and NY PEMV as adults with 31 and 47% efficiency, respectively, after a 48-hr acquisition-access period (AAP). None was as inefficient in transmission as the WARF biotype which was unable to transmit CALIF PEMV and transmitted NY PEMV to only 15% of the test plants. The remaining 16 colonies had an average transmission efficiency of 11.6% for CALIF PEMV and 22.5% for NY PEMV. In additional tests with adults of Biotypes EL and WARF, the EL biotype transmitted both virus strains to significantly ( P < 0.05) more plants than did Biotype WARF after AAP's of 12, 24, and 48 hr. Biotype WARF adults did not transmit CALIF PEMV until a 96-hr AAP was provided and then transmission was low (5-9.1%). Biotype EL nymphs were 100% efficient in transmitting both virus strains after a 48-hr AAP, whereas only 41.7 and 52.9% of the WARF biotype transmitted CALIF and NY PEMV, respectively. When both biotypes were reared on common vetch, Vicia sativa L., young adults transmitted the NY strain with significantly ( P <0.05) higher success after an AAP of 48 hr at either 13 or 25°C than when they were reared on broad bean, Vicia faba L. Highest transmission probability resulted from AAP's at 13°C. After a 4-hr AAP by 1st instars of Biotypes EL, WARF, and a 2nd biotype from East Lansing (EL1), PEMV was transmitted by the 2 EL Biotypes with similar characteristics and after shorter latent periods, to more plants per aphid generation, and for longer periods than was achieved by Biotype WARF. However, the 2 EL Biotypes differed significantly in size and fecundity; Biotypes ELi and WARF were inseparable on these bases. The transmission efficiency of Biotype EL remained at, or near, 100% until the death of the test aphids, whereas the efficiency of Biotypes EL1 and WARF declined with vector age.