U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


Date of this Version


Document Type



Agricultural Research Magazine 60(5): May-June 2012 pp. 20-21; ISSN 0002-161X


When an aphid, leafhopper, or psyllid lands on a plant to feed, it begins a process of chamical welfare. As piercing-sucking insects, they use needlelike stylets to insert saliva into plant tissues and open a pathway to ingest fluids critical to the plant’s survival. When punctured, the plant senses the attack and secretes proteins and other chemical defenses to prevent fluids from being pulled out, thus creating a stress on the plant. This warfare costs growers billions of dollars each year in lost ornamentals, vegetables, citrus, and other important agricultural crops.

Because much of the action takes place in the plant’s interior, a scientific tool called an “electrical penetration graph” (EPG) is critical for peering into the process. To use it, researchers connect the insect and plant to an electronic monitor that, like an electrocardiogram, reads electrical charges produced by tiny changes in voltage that occur as the insect feeds. A new type of EPG, developed by Elaine Backus, an ARS entomologist at the San Joaquin Valley Agricultural Sciences Center, in Parlier, California, and the late William Bennett, formerly from the University of Missouri, is giving scientists the clearest window yet into the wars waged between piercing sucking insects and the plants they infest. Because these insects are often carriers of plant pathogens that are transmitted through feeding, EPG can also illuminate how pathogens are injected into the plant to start the infection process.