Soybean plant defense responses elicited by insect vectors from two different feeding guilds

Plant response to herbivory is complex and is influenced by insect feeding guilds. Additionally, several insect herbivores vector pathogens resulting in the induction of both pathogen-induced and herbivore-induced plant defenses. There are no studies on plant responses to insect vectors from different feeding guilds. Our study system included the phloem-feeding soybean aphid that transmits several viruses such as Soybean mosaic virus and the cell-content feeding soybean thrips that transmits Soybean vein necrosis virus. The objectives of our study were: 1) to determine plant defense responses to infestation by insect vectors from the two different feeding guilds, and 2) to evaluate the effect of plant defense elicitor sprays in reducing population growth of insect vectors from the different feeding guilds. Non-viruliferous aphids solely activated SA pathway whereas viruliferous aphids activated SA pathway and to a lesser extent JA pathway. Non-viruliferous thrips induced JA pathway only and viruliferous thrips induced both SA and JA pathways. Interestingly, methyl jasmonate spray reduced aphid and thrips populations compared to SA spray. This is contradictory to gene expression analysis that indicated activation of SA pathway in response to aphid feeding, a potential decoy strategy by the aphids to suppress JA defenses via SA antagonistic crosstalk. To summarize, different defenses are activated against different guilds, however, resistance against soybean aphids and thrips is regulated by JA-mediated defenses in soybean. An understanding of resistance can be exploited for pest and disease management by utilizing elicitors of induced defense in plants.