Investigation of an expanded, lumped-element model of electropenetrography (EPG) and the accuracy of the traditional R and emf model

Authors: Backus, Elaine; PATTERSON, WILLIAM - Interdisciplinary Consulting Corporation (IC2)

Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2023
Publication Date: 3/29/2023
Citation: Backus, E.A., Patterson, W.C. 2023. Investigation of an expanded, lumped-element model of electropenetrography (EPG) and the accuracy of the traditional R and emf model. Computers and Electronics in Agriculture. 208. Article 107771. https://doi.org/10.1016/j.compag.2023.107771.
DOI: https://doi.org/10.1016/j.compag.2023.107771

Interpretive Summary: Among the most economically devastating pests in agriculture are insect vectors of plant and animal pathogens. Insect vectors transmit disease agents during specific feeding behaviors. Yet, it is extremely challenging to study feeding of vectors because they use piercing-sucking mouth parts to probe into opaque host tissues, and therefore feeding cannot be directly seen in real-time. There is an urgent need to accelerate research on feeding behaviors of piercing-sucking vectors, which can be accomplished using electropenetrography (EPG). First invented nearly 70 years ago, EPG has been widely used in studies of feeding biology of plant disease vectors, such as aphids, and has made possible all present knowledge of the role of feeding in transmission of plant diseases. Recently, EPG was extended to study blood-feeding vectors of animal diseases, such as mosquitoes and ticks, opening all-new opportunities to improve animal disease management. For EPG to achieve its highest usefulness, knowledge of its electronics must be updated so that better, more modern, versions of the instrument can be designed for use in the future. This paper represents a first step towards that goal. Our study used electrical engineering circuit analysis to determine whether there were unintended, unwanted elements in the EPG circuit and, if so, whether they could be removed by future instrument designers or users of EPG monitors. Results showed that some unwanted elements were present, and methods were identified to remove them. These findings provide important benchmark data for future studies of the nature of the electronic interaction between plant and insect. Together with the present study, such analysis will enable improvements in future EPG monitor designs.

Technical Abstract: Electropenetrography (EPG) allows measurement of feeding behaviors of piercing-sucking pests such as aphids and mosquitoes. The presently accepted electrical circuit model of an EPG monitor shows Vin (excitation voltage) applied to a feeding substrate such as a plant, which interacts with both Ra (a variable resistor that represents the feeding insect) and Vemf (biopotentials generated in the plant-insect interface). Together, Ra and Vemf interact with Ri (the input resistor of the first amplifier in the monitor). After signal processing, Vout (variable voltage output) results in waveforms that represent insect feeding. A lumped-element circuit analysis was performed to determine whether the above model was correct by today’s electrical engineering standards. Analysis showed that the above model was too simple to explain EPG signals. The newly developed model adds valuable information on parasitic effects such as capacitance in the amplifier (Ci) and from poor insect tethering (Cai), as well as effects of filtering due to induction (Lp) and capacitance (Cp) in the plant. Thus, designers and researchers must be alert to potential problems with parasitic elements in the EPG circuit and take actions recommended herein to reduce them. In addition, it was found that the insect is a complex electrical system, now symbolized by Za for impedance. Despite the findings of both parasitic and complex new elements in the EPG model, this work fundamentally supports the foundation of EPG science. That is, it confirms that the emf and still-named R components exist and can provide the basis for interpretation of EPG waveforms. These findings provide important benchmark data for future studies of the nature of Za, especially its importance in interpreting waveforms in the context of the crucial emf and R responsiveness curves. Together with the present study, such analysis will enable improvements in future EPG monitor designs.