Mechanisms of hopperburn: An overview of insect taxonomy, behavior, and physiology

Hopperburn is a noncontagious disease of plants caused by the direct feeding damage of certain leafhoppers and planthoppers. Although long studied-especially with Empoasca spp. leafhoppers (Cicadellidae: Typhlocybinae), the mechanisms underlying hopperbum have only recently been elucidated. Hopperburn is caused by a dynamic interaction between complex insect feeding stimuli (termed hopperbum initiation) and complex plant responses (termed the hopperbum cascade). Herein we review, the nature of the feeding stimuli in hopperbum initiation, especially for Empoasca spp., which we also compare with the planthopper Nilaparvata lugens. Contrary to previous reports, Empoasca hopperbum is not caused solely by toxic saliva. Instead, it is caused by a plant wound response triggered by a unique type of stylet movement. which is then exacerbated by saliva. Electrical penetration graph monitoring has revealed that all Empoasca spp. are cell rupture feeders, not sheath feeders, and that certain tactics of that feeding strategy are more damaging than others. Measuring the proportions of the most damaging feeding led to development of a resistance index, the Stylet Penetration Index, which can predict hopperbum severity in different plants or under different environmental conditions and can supplement or replace traditional, field-based resistance indices.