Eastern Beauty wulong is one of several so-called “bug-bitten teas” produced only from tea plants attacked by the tea green leafhopper (Empoasca onukii). Tea plants that are damaged by these leafhoppers respond by producing a blend of volatile compounds that may serve to attract natural enemies of the leafhoppers. The increase in volatile production by the tea leaves improves the quality of the tea by imparting a unique honey/fruit aroma to the final brew. Leafhoppers are cell-rupture feeders, only making tiny wounds on the underside of tea leaves. Although leafhopper damage does result in stunted growth and reduced yield, leafhoppers aren’t removing leaf area. Because the quality of damaged leaves is improved, tea farmers may choose to forgo pesticide applications and produce bug-bitten teas in the summer months when leafhoppers populations are high enough.
I’m interested in how leafhopper density affects the blend of metabolites produced by tea plants. Are all metabolites produced in a dose-dependent manner? This seems unlikely. It is more likely that the blend of metabolites depends on leafhopper density and there should be an optimal density of leafhoppers to produce the best flavor.
I’m also interested in how leafhopper population growth relative to tea shoot growth may change as the climate continues to warm. Insects are likely to benefit from increased warming because they will be able to emerge earlier and remain active longer. It is predicted that plants will benefit less from warming than insects due to increases in wasteful photorespiration at high temperatures. This could potentially shift the balance of the tea-leafhopper relationship from beneficial to pest.
To my knowledge, bug-bitten tea is the only crop in the world where farmers actually want more insect damage to improve quality, but perhaps this is true in other quality-centric crops, and we’ve just assumed herbivorous insects are always pests.