The AC-DC correlation monitor: New EPG design with flexible input resistors to detect both R and emf components for...

Much of what is known today about hemipteran feeding biology, as well as mechanisms of their host plant interactions and transmission of phytopathogens, has been learned via use of electrical penetration graph (EPG) technology, originally called electronic monitoring of insect feeding. Key to all of this information has been the electronic designs of EPG monitors. It has been 45 years since the publication of the original EPG, the AC monitor, and 30 years since introduction of the DC monitor, an important improvement for EPG science. Herein we describe our new AC-DC Correlation Monitor, the first major improvement in design since the DC monitor. We provide the monitor's block diagram and circuit description, and discuss (as a first example) its application to aphid feeding waveforms. Our instrument combines design features from the existing AC Missouri monitor and the DC Tjallingii monitor, plus several new innovations. It can produce three simultaneous, time-synchronized, output signals from a single insect, via AC and DC signal processing circuitry, as well as using either AC, DC, AC-plus-DC, or 0V substrate voltage. Our research conclusively demonstrates that AC signal processing can be designed to duplicate the level of detail and fidelity of aphid waveforms previously provided solely by the DC monitor, including all R- and emf-component waveforms. Availability of either AC or DC applied voltages will allow similar high-resolution recording of insects that appear to be sensitive to DC applied voltages. We also begin to determine the subtle reasons why published waveforms from older AC and DC monitors appear to differ so greatly. Our instrument is a single, flexible, universal monitor that can provide maximum, R-plus-emf waveform information from any piercing-sucking species, especially non-aphid species with sensitivity to DC applied voltage.