Effects of Soybean Vein Necrosis Virus on Life History and Host Preference of Its Vector, Neohydatothrips variabilis, and Evaluation of Vector Status of Frankliniella tritici and Frankliniella fusca

Soybean vein necrosis virus (SVNV) is an emerging Tospovirus that is now considered to be the most widespread soybean virus in the United States. SVNV is transmitted from plant-to-plant by soybean thrips, Neohydatothrips variabilis (Beach). We hypothesized that a positive interaction between the host plant, SVNV, and the vector may have resulted in the widespread distribution of the virus in a short span of time. Our study found that SVNV-infected N. variabilis females produced significantly more offspring compared with non-infected females. No other life-history trait varied between SVNV-infected and non-infected thrips. There was considerable variation in SVNV copy number in infected thrips ranging from 10² -10⁶. Moreover, there was a significant negative correlation between SVNV copy number and fecundity in infected N. variabilis. This suggests that excessive virus accumulation may result in lower viability of N. variabilis. In choice tests, SVNV-infected N. variabilis preferred to feed on non-infected leaflets compared with infected leaflets. Vector competence assays indicated that Frankliniella tritici and Frankliniella fusca can transmit SVNV, but at a lower efficiency than N. variabilis. Comparison of life history of between the primary and secondary vectors showed that N. variabilis had the highest fecundity, but F. tritici had the shortest development time and greatest larval survival. Taken together, the increased fecundity of SVNV-infected N. variabilis, their apparent preference for non-infected host plants, in conjunction with the ability of secondary vectors to survive and reproduce on soybean may, in part, explain the rapid spread of SVNV in the United States.