Master of Science (MS)
Plants are attacked by a variety of herbivore feeding guilds and respond with specific responses to specific attacks, which may be localized or systemic. How a plant defends against one feeding guild may alter the plant’s response against a different feeding guild. A better understanding of these interactions will allow for the development of refined pest management programs. One situation in which this may occur is in interactions between chewing and piercing/sucking herbivores, such as aphids. Aphids are important crop pests primarily due to their ability to transmit viruses, the efficacy of which can be affected by plant defenses. To determine if systemic induction has an effect on aphid feeding behaviors, three soybean varieties, (Progeny 4906RR, Davis, and Lyon) were induced with either soybean looper (SBL), Chrysodeixis includes (Walker), larvae, foliar jasmonic acid, or foliar salicylic acid. Three days post induction, green peach aphid (GPA), Myzus persicae (Sulzer), apterae feeding behavior was recorded on induced and control plants using the Electrical Penetration Graph (EPG) technique. SBL feeding bioassays were used to assess the effect of previous SBL herbivory, JA or SA on SBL larval weight, and to confirm systemic 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 SBL does not induce a defensive response in Davis. SA did not induce a response in either variety. Neither herbivory nor JA had an effect on SBL larval weight in Lyon, suggesting it does not induce a defensive response. However, SA increased SBL larval weights. SBL herbivory decreased several behaviors associated with nonpersistant virus transmission in both Progeny and Davis, but had no effect on aphid feeding behavior in Lyon. Jasmonic acid induction increased several behaviors associated with nonpersistant virus transmission in both Progeny and Davis. Exogenous SA application also increased behaviors associated with nonpersistant virus transmission in all three varieties. These results suggest that inducing host plant resistance using exogenous JA application may have positive effects by reducing herbivore performance. However, both JA and SA may potentially have negative impacts by increasing nonpersistant virus transmission.
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Dryburgh, John L., "Herbivore Response to Soybean Under Differing Induction Methods" (2015). LSU Master's Theses. 2813.