Aphids as vectors of peanut mottle virus

Higher percentages of peanuts than soybeans or cowpeas become infected when these crops are growing equal distances from a source of peanut mottle virus (PMV). The total number of aphids trapped in these crops are about equal and the reason for this differential percentage infection has not been demonstrated. Known vectors of PMV such as Aphis craccivora (Koch) and Myzus persicae (Sulzer) comprised 31% of the aphid population in peanuts compared to 14% in soybeans and 17% in cowpeas and could be responsible for the higher number of peanut infections. In addition, trapping of live aphids in peanut fields showed that viruliferoup Rhopalosiphum maidis (Fitch) were present. Laboratory studies confirmed that R. maidis could transmit PMV from peanut to peanut. This is the first report of R. maidis as a vector of PMV.

Virus transmission tests using 5 aphids per peanut seedling were conducted in the greenhouse. Myzus persicae (Sulzer), Aphis craccivora (Koch), and Rhopalosiphum maidis (Fitch) were able to vector peanut mottle virus from peanut to peanut 30, 14, and 4%, respectively. In subsequent tests, where only one aphid was used per test seedling, M. persicae, A. craccivora, and R. maidis transmitted PMV at 9, 4, and 2%, respectively. The retention abilities of the three aphid species tested for PMV was low when compared to other experiments (20). Switching varieties from Florigiant to Florunner did not appear to significantly increase virus transmission rates of any of the aphid species tested in comparison to tests done with Florigiant. This is the first report of transmission testing with these three aphid species and PMV V745-473, a strain of the virus isolated from soybean in Virginia and with the Florigiant variety of peanuts.

In feeding preference tests, all three aphid species tested showed a preference for settling onto a host, regardless of the host species used, to wandering at random in the feeding arena and not feeding on any host plant. A. craccivora showed the greatest propensity to wander, with only 33% of those aphids tested choosing to settle on a host. In contrast, 58% of R. maidis tested chose to settle on a host.

In comparisons of feeding preferences between combinations of two host plants, M. persicae preferred chinese cabbage in 4 comparisons and soybean in 2, A. craccivora preferred both soybean and chinese cabbage in 2 comparisons each, and R. maidis preferred chinese cabbage in 4 comparisons and sorghum in 3. Chinese cabbage, soybeans, cowpeas and sorghum are preferred by these three aphid species over peanuts. Based on feeding preference it would be impossible to separate the PMV vectoring ability of these three aphid species.

The three aphid species tested were able to reproduce well on the plants on which they were reared, but only A. craccivora was able to reproduce on peanuts.