Alate aphid (Homoptera: Aphididae) species and their relative importance as field vectors of soybean mosaic virus.
A technique was developed and employed in central Illinois to trap and assay aphid alatae for the incidence of soyabean mosaic virus (SMV) transmission among naturally occurring transient aphid populations downwind of a field of infected soyabean. In 1976 and 1978, 1709 alate aphids were trapped alive and assayed, and 4.2% were found to transmit SMV. Aphis craccivora Koch, Macrosiphum euphorbiae (Thos.), Myzus persicae (Schulz.), Rhopalosiphum maidis (Fitch) and R. padi (L.) accounted for more than 93% of the transmissions. At least 55 additional species were assayed, 5 of which transmitted only once; others did not transmit. Because virus infection during the early growth stages of soyabean increases the loss of yield and the percentage of seed-borne virus, vector species that tended to fly in mid- to late spring were considered, from an economic point of view, more important in the spread of SMV. R. maidis flew in mid- to late summer and in autumn. R. padi was not abundant at any time of year and its transmission efficiency was low. M. persicae tended to fly in mid-summer. Two species (A. craccivora and Macrosiphum euphorbiae), which had major flights in late spring and early summer and relatively high transmission efficiencies, were potentially important in the economic spread of SMV in central Illinois. A third species, A. citricola v.d. Goot, may also have been important because it flew in late spring and laboratory data suggested that it was a relatively efficient vector of SMV. A. citricola was not assayed by the technique because trapping took place in the morning and this species apparently flew later in the day.