Ecological engineering in a teacup
In the Wuyi Mountains of China's Fujian province, a UNESCO World Heritage site, the tea plant Camellia sinensis faces a persistent threat. The tea green leafhopper, Empoasca onukii, is a sap-sucking insect that can cause significant damage to tea leaves, reducing both yield and quality. While chemical pesticides are one solution, a growing interest in organic and sustainable farming has led researchers to explore ecological engineering—manipulating the farm environment to manage pests naturally. One of the most effective methods is intercropping, the practice of planting other crops alongside the main cash crop.
Controlled studies in the Wuyi Mountains and other tea-growing regions of China have tested the effectiveness of various companion plants. The goal is to find plants that either repel the leafhoppers or attract their natural enemies. By creating a more diverse agroecosystem, farmers can reduce their reliance on pesticides and promote a healthier environment. This approach turns the tea plantation into complex interactions where pests are kept in check by a thriving population of predators.
A push-pull experiment
The strategy often involves a "push-pull" approach. Some companion plants "push" pests away with repellent volatile organic compounds (VOCs), while others "pull" in beneficial predators. Scientists have measured the specific effects of intercropping various aromatic and leguminous plants with tea. For example, planting lavender (Lavandula pinnata) has been shown to repel tea green leafhoppers due to the odors it releases. Similarly, intercropping with marigold (Tagetes erecta) and Flemingia macrophylla can reduce leafhopper populations by releasing a blend of volatile attractants, including cis-3-hexen-1-ol and α-farnesene.
The "pull" part of the strategy is just as important. Intercropping tea with plants like Cassia tora significantly increases the populations of natural leafhopper enemies, such as ladybird beetles, lacewings, and spiders. In some experiments, the diversity of important spider predators increased, helping to suppress the leafhopper population. Studies on intercropping with cover crops like Chamaecrista rotundifolia have found that they provide better microhabitats for predators to build nests and find shelter, boosting their numbers. The results are ecological and intercropping with legumes like soybeans and cowpeas can also increase the foliar concentrations of desirable compounds in the tea leaves themselves, such as caffeine and theanine, thereby improving the tea's final quality.