Insect herbivores from different feeding guilds induce different signaling pathways in plants. In this study, we examined the effects of salicylic acid (SA)-and jasmonic acid (JA)-mediated defenses on performance of insect herbivores from two different feeding guilds: cellcontent feeders, soybean thrips and phloem feeders, soybean aphids. We used a combination of RT-qPCR analysis and elicitor-induced plant resistance to determine induction of SA and JA signaling pathways and the impact on herbivore performance. In the early interaction between the host plant and the two herbivores, SA and JA signaling seems to occur simultaneously. But overall, soybean thrips induced JA-related marker genes, whereas soybean aphids increased SA and ABA-related marker genes over a 24-h period. Populations of both soybean thrips and soybean aphids were reduced (47 and 25 %, respectively) in methyl jasmonate (MeJA)-pretreated soybean plants. SA treatment has no effect on either herbivore performance. A combination pretreatment of SA and MeJA did not impact soybean thrips population but reduced soybean aphid numbers which was comparable with MeJA treatment. Our data suggest that SA-JA antagonism could be responsible for the effect of hormone pretreatment on thrips performance, but not on aphid performance. By linking plant defense gene expression and elicitor-induced resistance, we were able to pinpoint the role for JA signaling pathway in resistance to two herbivores from different feeding guilds.

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 10(2) -10(6) 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.

Thrips-infesting soybeans were considered of minor economic importance, but recent evidence of their ability to transmit a newly identified soybean virus, Soybean vein necrosis virus (SVNV), has raised their profile as pests. Season-long surveys were conducted using suction traps to determine the effects of temperature and precipitation on the spatiotemporal patterns of three vector species of SVNV, Neohydatothrips variabilis (Beach) (Thysanoptera: Thripidae) (soybean thrips), Frankliniella tritici (Fitch) (Thysanoptera: Thripidae) (eastern flower thrips), and Frankliniella fusca (Hinds) (Thysanoptera: Thripidae) (tobacco thrips) in soybean fields in Indiana in 2013 and 2014. In addition, soybean fields were surveyed for presence of SVNV in both years. We found that the magnitude and timing of thrips activity varied greatly for the three species. N. variabilis activity peaked in mid-August each year. The peak activity for F. tritici occurred between late-June, and a second peak in activity was observed in early-August, while F. fusca activity remained more or less the same with no peak. There was no gradient in thrips populations from southern to northern locations. This suggests that these insects are not migratory and may overwinter in soil or perennial noncrop host plants and other weed hosts in Indiana. The capture rates of N. variabilis and F. tritici were only related to temperature, and capture rates of F. fusca were not related to either variable. SVNV was first detected in mid-late August, which coincided with the peak of the primary vector, N. variabilis. The virus was not detected earlier in the season despite peaks in F. tritici activity. Our results may be used in weather-based models to predict both thrips dynamics as well as SVNV outbreaks.