Effects of Thiamethoxam Seed Treatments on Soybean Aphid (Hemiptera: Aphididae) Feeding Behavior

Abstract

Since its discovery in North America in 2000, the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), has rapidly become an important pest of soybean [Glycine max (L.) Merrill], sometimes resulting in significant yield losses. Previous research has documented the toxicity of neonicotinoid seed treatments to soybean aphids, but control under field conditions has been inconsistent. Imidacloprid, a popular neonicotinoid insecticide, has been shown to exhibit antifeedant effects on aphids. Antifeedant activity has not been demonstrated for other neonicotinoids, including thiamethoxam. This research investigated the effects of a thiamethoxam seed treatment on soybean aphid feeding behavior by using electronic penetration graphs (EPG) to visualize stylet penetration behavior. Soybean aphid feeding behavior was assessed for 9 h on thiamethoxam-treated and untreated soybeans (V2 and V4 stages). Because results were inconclusive from initial experiments, a study was conducted to document the effects of thiamethoxam-treated soybeans on soybean aphid survival. The seed treatment was shown to negatively affect aphid survival at 4, 8, and 11 d after aphid introduction. A subsequent EPG study then was designed to document soybean aphid feeding behavior for 15 h, after an initial exposure of 9 h to thiamethoxam-treated soybeans. In this study, the exposed aphids exhibited significant differences in feeding behavior compared with those aphids feeding on untreated soybeans. Soybean aphids on thiamethoxam-treated soybeans spent significantly less time feeding in the sieve element phase, with a greater duration of nonprobing events. These studies suggest soybean aphids are unable to ingest phloem sap, which may be another important element in seed treatment protection.

Uptake and translocation of imidacloprid, clothianidin and flupyradifurone in seed‐treated soybeans

“…Even with a decline in insecticidal activity, a substantial amount of time would be needed for the aphid population to reach damaging levels. Similarly, other studies have reported significant soybean aphid mortality within 1–4 days of exposure to neonicotinoid‐treated soybeans …”

Characterization of Greenbug Feeding Behavior and Aphid (Hemiptera: Aphididae) Host Preference in Relation to Resistant and Susceptible Tetraploid Switchgrass Populations

“…At the completion of the starvation period, wired aphids were placed on the adaxial side of the newest, fully developed leaf. Aphid placement was considered successful if the individual was able to move freely on the leaf surface [46]. Plants on which no feeding occurred or for which no reliable signals were obtained were not included in further analyses.…”

“…Plants on which no feeding occurred or for which no reliable signals were obtained were not included in further analyses. All plants, EPG probes, and plant electrodes were placed inside one of two Faraday cages, constructed from aluminum mesh wire with an aluminum frame and base (61 cm×61 cm×76 cm), in order to protect the EPG's internal conductors from electrical and environmental noise [10,46]. Recordings were made on eight plants simultaneously, with at least one plant of each of the three switchgrass populations represented in each recording.…”

“…The pathway phase (waveforms A, B, and C) is characterized by intercellular stylet penetration and withdrawal, periods of no stylet movement, and brief intracellular punctures by stylet tips, also known as potential drops (waveform pd) [22,36]. For simplification, differences between waveforms A, B, and C were not defined in the study and the three waveforms were generically labeled as waveform C [1,16,46]. Waveform F (stylet penetration problems) were not common in the recordings and were included in the pathway phase whenever they were observed [11].…”

“…The sieve element phase reflects salivation secretions (waveform E1) and ingestion of phloem sap (waveform E2). Waveforms E1 and E2 can be difficult to distinguish; therefore, the two waveforms were combined and labeled generally as waveform E to depict general penetration activities of S. graminum in phloem tissues [2,3,46]. EPG feeding behavior parameters were selected from the Sarria Excel Notebook [40].…”