Probing behavior analysis of foxglove aphids on soybean genotypes using the DC-EPG system

Abstract

The foxglove aphid (FA), Aulacorthum solani, is a soybean pest that threatens food security. However, few studies on soybean plant resistance to FAs with resistance to Aulacorthum solani (Raso) genes have been conducted in Korea and Japan. Understanding how FAs infiltrate soybean plant tissues and identifying the location of resistance are crucial for the effective management of insect pests. This study focused on evaluating the probing behavior of FAs that fed on three susceptible and five (moderately and highly) resistant soybean genotypes using the electrical penetration graph (EPG) technique. We used EPG to visualize the movement of the aphid stylet and probing behavior in soybean tissues. We carefully studied the eight distinct waveforms generated during 14 h of feeding. The susceptible genotypes exhibited shorter duration and frequency of non-probing (np) waveforms but higher duration and frequency of E2 waveforms. In contrast, moderately and highly resistant genotypes produced fewer E2 waveforms but more np waveforms. The lower frequency and duration of the E2 waveform values from the resistant genotypes indicated that the resistance factor was located in the phloem. Therefore, phloem defense mechanisms inhibit FA activity. This pioneering study characterized the probing behavior of FAs in various soybean genotypes. Understanding the variations in FA probing behavior across different genotypes is useful for elucidating the mechanism of FA resistance and can guide future research on plant-insect interactions to assist in selecting resistant genotypes.