Pest or blessing: analysing the tea green leafhopper.
When it comes to green tea production, there is no other pest that causes more devastation than the tea green leafhopper. Found throughout Asia, including China, Taiwan and Japan, the damage from the insect can reduce yields from 15 percent to 50 percent. Left untreated, the damage from the insects is extensive, causing the leaves to fall off and die. However, finding an effective pest management strategy to control these insects has been particularly challenging. This was partially because, although similar insects were identified throughout the tea-planting regions in Asia, it was not clear if they were the same insect.
In fact, the tea green leafhopper has been provided with several scientific names including Empoasca vitis (Goethe), Jacobiasca formosana (Paoli) and Empoasca onukii Matsuda. However, the September 2015 research study, Clarification of the Identity of the Tea Green Leafhopper Based on Morphological Comparison between Chinese and Japanese Specimens, confirmed that the tea green leafhoppers in mainland China, Taiwan and Japan, are a single species. This research was a critical piece to help establish an effective integrated pest management strategy across a variety of regions. Now, researchers could focus on the biology and adaptation of the insect to develop effective control strategies.
Understanding the biology of this insect is particularly necessary for those farmers who may want to encourage controlled insect damage on a proportion of their plants. These producers have identified that, in fact, some leafhopper damage when producing oolong can be beneficial.
The original story of Oriental Beauty oolong is thought to be traced back to World War II. It is believed that during the war, the farmers were forced to abandon their fields for an entire season. When the farmers returned, they found their fields damaged by the leafhopper, and most farmers made the decision to abandon their crop for the year. However, there was one exception, a Taiwanese farmer in the Hsin Chu county who not only processed the tea, but ended up selling it for a high price. The tea was praised for it's high quality. The farmer proudly told his friends about the high price he earned for the tea, earning the name Pong Fong Cha (Braggers Tea). The name Oriental Beauty is said to have come from the Queen of England, who was impressed by the quality and flavour of this new tea from the Orient.
Today, this bug-bitten tea is being replicated in several regions within Asia, with farmers actively encouraging a degree of plant damage from the tea green leafhopper. There are two theories of where the flavour comes from. The first is that the bite from the insect triggers a chemical reaction within the plant, perhaps a defence mechanism, which brings about the sweet flavour that the tea has become known for. The second theory is that the bite marks start the oxidization process enhancing the flavour profile.
Eric Scott, PhD candidate in the biology department at Tufts University, Meaford, Massachusetts, is currently researching the exact mechanism that brings about the flavour change in the plant, including how the insect positively impacts plants when processing oolong. "There is no question that this is a major pest for green tea," said Scott. "But it just so happens that when processing oolong, the slightly damaged leaves create a sweet flavour and aroma, which has become known as Oriental Beauty oolong, or bug-bitten tea." Scott's research continues to look at the defence mechanism that the tea plants produce when damaged by the tea green leafhopper. It is this defence mechanism that the researchers believe creates the distinctive sweetness that is found in these bug-bitten leaves.
However, there is a damage sweet spot, too much damage, and the tea becomes bitter, where a little bit of damage increases the aroma and decreases the bitterness. Climate change, said Scott, is another factor that may influence the leafhopper population, either resulting in too many insects or large plants with not enough damage.
Understanding the Leafhopper
In one given year, there can be between 9-17 generations of the leafhopper insects, with the most serious damage occurring from June to September, when the population peaks and the temperatures begin to rise. The insects are most easily controlled in their infancy state, but even young, these pests are incredibly adaptive. Nocturnal by nature, the leafhoppers move quickly, leaping, flying and hiding amongst both the tea leaves and the nearby leaves and grasses. These quick movements can make it extremely difficult to apply contact insecticides to help reduce the population. While their daytime inactivity can make it challenging to locate where these night creatures are hiding.
For the young insect, both water irrigation and wind has been an effective treatment. These tools help to displace the insects, even when they are trying to hide amongst the leaves and nearby weeds. But as the insects mature, their bodies also adapt, increasing the brochosome density on their abdomens. These brochosomes allow them to adhere to the plants, making the wind and rain treatments largely ineffective.
In the spring of 2016, researchers, Vasseur Shi, Zeng Huang, Liu Hu et al, delved into studying how adult tea green leafhoppers behaviour changed with varying light conditions. Their hope was that understanding the biology of this insect may help to guide farmers in the best pest management strategies. Virtually all stages of the tea green leafhopper can cause significant damage to the tea plant with the nymphs and adults sucking sap from the young tea shoots and leaves.
The study revealed that the insects tend to be nocturnal, with the population increasing when temperature was above 26 degrees Celsius. "To enhance pest control efficiency, it may be useful to supplement the control of sticky cards that are used during the day with a light control system at night," reported Shi, Huang et al. This type of pest management will target the insects when they are most active.
The research on the green tea leafhopper plant is multi-faceted and includes trying to understand how warming might impact both the population density of the leaf hoppers and the growth of the plant. "What we are seeing in practice, is farmers avoiding spraying insecticides during the period of time that they want the insect damage," said Scott.
Some farm managers try to manually control the insect population by controlling the weeds and grasses that grow between the tea plants. "The leafhoppers tend to hide in the weeds," said Scott. "So, if the damage is too high, the farmer may remove the weeds to indirectly manage the leafhoppers, conversely, if the population is too low, they may allow the weeds to grow."
Scott is particularly interested in how farmers seem to know when the right amount of damage occurs. The theory is that it is the bite marks enhance the flavour of the oolong tea by initiating oxidation. The damage of the leafhopper appears as small brown dots on the underside of the leaf, with the leaf colour changing to a yellowish/ reddish hue. However, if the damage is extensive, the leaves can drop off, which is why it is particularly troublesome for farmers who are producing green tea.
The research between the relationship of the tea green leafhopper and the tea plant is a dynamic one. Understanding the nature of this insect and effective control mechanisms will help ensure that farmers can diversify their product offerings.
Anne-Marie Hardie is a freelance writer, professor and speaker based in Barrie, Ontario. She may be reached at: annemariehardiel@ gmail.com.
Caption: Brown stippling damage to the tea leaves caused by tea green leafhopper.
Caption: Oriental Beauty oolong or bug-bitten tea.
Caption: Shanfu Tea Farm in Shaxian, Fujian Province, China, where research on the tea green leafhopper is being conducted.
Caption: The tea green leafhopper is beneficial to oolong tea but damaging to green tea.
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|Title Annotation:||SPECIAL SERIES PART III: TEA GREEN LEAFHOPPER|
|Comment:||Pest or blessing: analysing the tea green leafhopper.(SPECIAL SERIES PART III: TEA GREEN LEAFHOPPER)|
|Publication:||Tea & Coffee Trade Journal|
|Date:||May 1, 2017|
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