Defining Toxicological Endpoints of Aphis Gossypii Feeding

The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is a destructive agricultural pest, due to photosynthate removal and plant virus transmission. This project consisted of two main goals. First, we employed toxicity bioassays and electrical penetration graph (EPG) methodology to quantify changes to feeding behavior and toxicity of A. gossypii after exposure to commercialized aphicides. Commercialized aphicides containing flupyradifurone, sulfoxaflor, thiamethoxam, thiamethoxam + lambda cyhalothrin, and bifenthrin induced \u3e 90% aphid mortality within 4 hours of exposure. This was supported by our EPG results that showed a significant reduction in the proportion of aphids that continued to probe on cotton 4 hr after exposure to flonicamid, thiamethoxam, flupyradifurone, bifenthrin, and thiamethoxam premixed with lambda cyhalothrin. Furthermore, flupyradifurone induced an LT50 of 8.9 min after exposure. Lastly, phloem feeding was significantly reduced for flupyradifurone, flonicamid, thiamethoxam, sulfoxaflor, and thiamethoxam. In the second goal, we aimed to test the antifeedant properties of small-molecule inhibitors of inward rectifier potassium (Kir) channels expressed in the aphid salivary glands. Two Kir channel inhibitors, VU041 and VU730, reduced the secretory activity of the aphid salivary gland by 3.3-fold and importantly, foliar applications of VU041 and VU730 significantly increased the time to first probe, total probe duration, and nearly eliminated ingestion of phloem. Although promising, foliar applications of chemicals have significant pitfalls including non-target toxicity and increased costs of application. Thus, we tested the capability of a novel natural product based solubilizer to increase systemic movement of VU041 and VU730, which are highly lipophilic molecules. To study systemic movement throughout the plant and across the leaf surface, the adaxial side of a single cotton plant leaf was treated with a Kir inhibitor solubilized into the water-soluble concentrate. Upper leaves were infested with aphids 60-72 hours after chemical treatment and changes to feeding behavior were quantified through EPG methodology. Trans-laminar and translocation of Kir modulators was confirmed as we observed a significant reduction of aphids able to reach phloem. These data further support hemipteran Kir channels as a target to prevent feeding and plant virus transmission through novel delivery mechanisms that enable plant systemic movement