Mechanisms of hopperburn: an overview of insect taxonomy, behavior, and physiology.

Hopperburn is a non-contagious 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 hopperburn have only recently been elucidated. Hopperburn is caused by a dynamic interaction between complex insect feeding stimuli (termed hopperburn initiation) and complex plant responses (termed the hopperburn cascade). Herein we review the nature of the feeding stimuli in hopperburn initiation, especially for Empoasca spp., which we also compare with the planthopper Nilaparvata lugens. Contrary to previous reports, Empoasca hopperburn 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 hopperburn severity in different plants or under different environmental conditions and can supplement or replace traditional, field-based resistance indices.

Sex pheromone of the pink hibiscus mealybug, Maconellicoccus hirsutus, contains an unusual cyclobutanoid monoterpene.

Two compounds that together constitute the female sex pheromone of the pink hibiscus mealybug (PHM), Maconellicoccus hirsutus, were isolated, identified, and synthesized. They are (R)-2-isopropenyl-5-methyl-4-hexenyl (S)-2-methylbutanoate [common name is (R)-lavandulyl (S)-2-methylbutanoate] and [(R)-2,2-dimethyl-3-(1-methylethylidene)cyclobutyl]methyl (S)-2-methylbutanoate [which we refer to as (R)-maconelliyl (S)-2-methylbutanoate]. Maconelliol is an unusual cyclobutanoid monoterpene, and its structure has been established by enantioselective synthesis from precursors of known structure and configuration. A 1:5 synthetic mixture of the two RS esters (1 microg per rubber septum) proved to be a potent attractant of males in field bioassays. The pheromone component, maconelliyl 2-methylbutanoate, represents a heretofore undescribed natural product.