Effects of soybean looper and jasmonic acid induction on green peach aphid feeding behavior in soybean

Aphids are important crop pests, damaging plants through photosynthate removal and by vectoring viruses.  Aphids are efficient vectors due to host selection and feeding behaviors.  Factors that change aphid feeding behavior may be used to reduce virus transmission.  Induced resistance is known to affect herbivore feeding behavior and has the potential to alter virus acquisition and inoculation.  Soybean varieties Progeny 4906RR and Davis were induced by: (1) allowing third instar soybean looper (SBL), Chrysodeixis includes (Walker), larvae to feed for 24 hr, or (2) by spraying with 2 mM JA.  Three days post induction, green peach aphid (GPA), Myzus persicae (Sulzer), apterae feeding behavior was recorded on the top most trifoliate of induced and un-induced plants using the Electrical Penetration Graph (EPG) technique.  SBL feeding bioassays were used to confirm induction.  Both previous herbivory and JA reduced SBL larval weights when fed Progeny 4906RR tissue, while herbivory had no effect on SBL larval weights when fed Davis tissue, suggesting Davis does not induce a defensive response to SBL.  SBL herbivory had no effect on GPA feeding behaviors related to virus transmission in either variety.  GPA tended to have a greater number of probes on JA treated Progeny 4906RR than control plants.  GPA had significantly longer subphase II-1 durations and tended to have longer probe durations on JA treated Davis soybeans.  These results suggest that inducing host plant resistance using exogenous JA application may have positive effects by reducing herbivore performance, but could have negative impacts by increasing virus transmission.