Tea Geometrid Research Articles

Herbivore species, infestation time, and herbivore density affect induced volatiles in tea plants

In response to insect herbivory, plants emit volatiles that are used by the herbivores’ natural enemies to locate their host or prey. Herbivore attack also enhances tea aroma. Herbivore-induced plant volatiles (HIPVs) vary both quantitatively and qualitatively with infestation duration and herbivore density. Thus, whether HIPVs can reliably communicate the identities of herbivores is of interest. Here, we studied the tea plant volatiles induced by the tea leafhopper (Empoasca vitis, a piercing–sucking insect), the tea geometrid (Ectropis oblique, a chewing insect), and methyl jasmonate (MeJA, a plant hormone). Geometrid feeding induced more complex volatile blends than did leafhopper infestation. The volatiles induced by both herbivores significantly increased in quality and quantity with time during the first 16 h of infestation, after which the profiles of induced volatile blends and the emission of induced compounds varied diurnally. (E)-β-Ocimene displayed a unique rhythm in which emission peaked at night. The amount of HIPVs significantly increased, while their profiles changed little, with herbivore density. Overall, the leafhoppers and geometrids induced significantly different volatiles from tea plants, while the HIPV profiles varied with a circadian rhythm and were similar at different herbivore densities. Our findings also suggest a new method of enhancing tea flavor using exogenously applied plant hormones, because the volatiles induced by leafhoppers and MeJA were similar in general composition.

Regurgitant Derived From the Tea Geometrid Ectropis obliqua Suppresses Wound-Induced Polyphenol Oxidases Activity in Tea Plants

Polyphenol oxidases (PPOs) have been reported to play an important role in protecting plants from attack by herbivores. However, little is known about their role in tea. Here, we investigated the effect of PPOs on interactions between tea plants and the tea geometrid Ectropis obliqua, one of the most important insect pests of tea. Jasmonic acid (JA) treatment resulted in increases in PPO activity, and the effect of JA was dose dependent. Ectropis obliqua caterpillars grew and developed more slowly on JA-treated tea plants than on control plants, and larval weight gains depended on the JA dosage. Artificial diet complemented with PPOs reduced the growth and survival rate of E. obliqua caterpillars, and there was a negative relationship between PPO level and larval growth and survival. Unlike mechanical wounding, which is an effective inducer of tea plant PPO activity, wounding plus the herbivore regurgitant or herbivore infestation suppressed the wound-induced PPO activities, especially at 4 days after treatment. These results suggest that PPOs are an important anti-herbivore factor in tea plants, defending them against E. obliqua larvae, and that E. obliqua larvae have evolved to elude the tea plant's defense by inhibiting the production of PPOs.