Catalyzing systemic movement of inward rectifier potassium channel inhibitors for antifeedant activity against the cotton aphid, Aphis gossypii (Glover).

BACKGROUND: The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is a destructive agricultural pest, capable of photosynthate removal and plant virus transmission. Therefore, we aimed to test the antifeedant properties of small-molecule inhibitors of inward rectifier potassium (Kir) channels expressed in insect salivary glands and develop an approach for enabling systemic movement of lipophilic Kir inhibitors. RESULTS: Two Kir channel inhibitors, VU041 and VU730, reduced the secretory activity of the aphid salivary glands by 3.3-fold and foliar applications of VU041 and VU730 significantly (P < 0.05) increased the time to first probe, total probe duration, and nearly eliminated phloem salivation and ingestion. Next, we aimed to facilitate systemic movement of VU041 and VU730 through evaluation of a novel natural product based solubilizer containing rubusoside that was isolated from Chinese sweet leaf (Rubus suavissimus) plants. A single lower leaf was treated with Kir inhibitor soluble liquid (KI-SL) and systemic movement throughout the plant was verified via toxicity bioassays and changes to feeding behavior through the electrical penetration graph (EPG) technique. EPG data indicate KI-SL significantly reduced ability to reach E1 (phloem salivation) and E2 (phloem ingestion) waveforms and altered plant probing behavior when compared to the untreated control. High-performance liquid chromatography (HPLC) analysis indicated the presence of VU041 and VU730 in the upper leaf tissue of these plants. Together, these data provide strong support that incorporation of rubusoside with Kir inhibitors enhanced translaminar and translocation movement through the plant tissue. CONCLUSION: These data further support hemipteran Kir channels as a target to prevent feeding and induce toxicity. Further, these studies highlight a novel delivery approach for generating plant systemic activity of lipophilic insecticides. © 2022 Society of Chemical Industry.

Profile of commercialized aphicides on the survivorship and feeding behavior of the cotton aphid, Aphis gossypii.

The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is one of the most destructive agricultural pests due to photosynthate removal and horizontal transmission of plant viruses. Horizontal transmission of plant viruses by aphids occurs during distinct feeding behavioral events, such as probing for non-persistent viruses or phloem feeding for persistent viruses. We employed toxicity bioassays and electrical penetration graph (EPG) methodology to compare toxicity and 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 >90% aphid mortality within 4 h of exposure. Flupyradifurone was the most acutely toxic aphicide studied with an LT50 of 8.9 min after exposure, which was approximately 3-fold lower than bifenthrin and thiamethoxam + lambda cyhalothrin. This was supported by our EPG results that showed a significant reduction in the proportion of aphids that continued to probe on cotton 4 h after exposure to flonicamid, thiamethoxam, flupyradifurone, bifenthrin, and thiamethoxam + lambda cyhalothrin. The commercialized aphicides containing spirotetramat, flonicamid, thiamethoxam, flupyradifurone, bifenthrin, sulfoxaflor, and pymetrozine significantly (P < 0.05) decreased the time to first probe when compared to the untreated control. Lastly, E1 (phloem salivation) and E2 (phloem ingestion) waveforms were significantly (P < 0.05) reduced for flupyradifurone, flonicamid, thiamethoxam, sulfoxaflor, and thiamethoxam. These data provide a comparative study for the development of new aphicides aiming to induce acute lethality and reduce aphid transmission of plant viruses.

ATP-sensitive inward rectifier potassium channels reveal functional linkage between salivary gland function and blood feeding in the mosquito, Aedes aegypti.

Reducing saliva secretions into the vertebrate host reduces feeding efficacy by most hematophagous arthropods. However, seminal studies suggested saliva is not a prerequisite for blood feeding in Aedes aegypti. To test this paradigm, we manually transected the salivary duct of female A. aegypti and an inability to salivate was correlated to an inability to imbibe blood. These data justified testing the relevance of inwardly rectifying potassium (Kir) channels in the A. aegypti salivary gland as an antifeedant target site. Pharmacological activation of ATP-gated Kir (KATP) channels reduced the secretory activity of the salivary gland by 15-fold that led to near elimination of blood ingestion during feeding. The reduced salivation and feeding success nearly eliminated horizontal transmission and acquisition of Dengue virus-2 (DENV2). These data suggest mosquito salivation is a prerequisite for blood feeding and provide evidence that KATP channels are critical for salivation, feeding, and vector competency.