Acquisition, retention and transmission of faba bean necrotic yellows virus by two of its aphid vectors, Aphis craccivora (Koch) and Acyrthosiphon pisum (Harris)

Faba bean necrotic yellows virus (FBNYV) belongs to a new group of plant viruses that have unusually small isometric virions and a multipartite ssDNA genome. It is the causal agent of some virus diseases affecting several food and fodder legumes in west Asia and north Africa. FBNYV is persistently transmitted by various aphid species of which Aphis craccivora appears to be the most significant natural vector. In attempts to obtain a better understanding of factors involved in FBNYV spread under field conditions, the interactions of the virus with A. craccivora and Acyrthosiphon pisum were studied. The two species were efficient vectors and very similar in their minimum acquisition (AAP) and minimum inoculation access feeding periods which ranged from 15 to 30 min and 5-15 min, respectively. Following an AAP of 72 h and daily serial transfers of individual aphids to single plants, many individuals retained and transmitted the virus throughout their life span (up to 32 days) but at erratic efficiencies. In this persistence experiment A. pisum was a more efficient vector than A. craccivora. For both aphid species no decrease in transmission efficiency was observed, suggesting that nymphs acquired large amounts of FBNYV virions which were not depleted in their hemocoel during the experiment. Based on log-probit analysis, median latency period (LP50) values of 108.8 h and 105.0 h were calculated for FBNYV in A. craccivora and A. pisum, respectively. FBNYV was not lost during moults and was not passed on to the parthenogenetic offspring by viruliferous adults. Aphids which acquired FBNYV as adults were strikingly poor vectors as compared to nymphs.