Ancient Tea trees are an important natural resource in China and a significant source of income for tea farmers in some southwestern regions. In recent years, the issue of protecting ancient tea tree resources in our country has become increasingly prominent. Climate change, excessive exploitation, neglect of protection and management have led to a growing severity of pest damage. Jingdong County, located in the central part of southwestern Yunnan and known as Yinsheng in ancient times, is home to lush ancient tea trees deep within the Wuliang Mountains. In August 2025, during my survey of ancient tea trees in this county, a tea farm manager approached me for advice. They mentioned that several ancient tea trees in their tea garden had been “ill” for several years, but they were unsure what kind of disease or pest was causing the problem. They urgently needed help to identify the cause so targeted control measures could be implemented to prevent more ancient tea trees in the garden from being affected.

Following the tea farm manager into the tea garden, I observed hundreds of ancient tea trees, each over a hundred years old, distributed throughout the garden. The plant diversity was rich (Figure 1). Due to the absence of pesticide and fertilizer use in the management process, the ecological environment was less disturbed, and there was no large-scale occurrence of diseases and pests, except for a small population of small green leafhoppers. However, a few ancient tea trees exhibited signs of decline, such as sparse leaves, yellowing foliage, and withered shoots.

Figure 1: Ancient tea trees in the Wukazhuang tea garden of Jingdong County, Pu'er City, Yunnan Province

Upon examining the affected ancient tea trees, no evidence of insect feeding on the leaves was found. However, some suspected boring holes were discovered at the base of the tree trunks. One severely affected tea tree had its trunk base cut open by the farm manager. From the cross-section, numerous boring holes were visible, primarily distributed in the wood, filled with wood shavings (Figure 2). Tracing along the boring tunnels, we found milky white, short-haired larvae (Figure 3), or pale yellow larvae with reddish-brown heads (Figure 4), as well as completely reddish-brown larvae (Figure 5). These were identified as wireworms at different developmental stages. Therefore, it was determined that several ancient tea trees in this tea garden were infested by wireworms. As a widely distributed pest worldwide, reports of wireworm damage on tea trees in China are relatively rare, and due to their habit of boring into the tree trunks, tea farmers are generally unfamiliar with them.

Figure 2: An ancient tea tree damaged by wireworm larvae and wood shavings accumulated at the root

Figure 3: Low-age wireworm larva

Figure 4: Wireworm larvae feeding on the trunk of an ancient tea tree

Figure 5: Last-stage wireworm larva on an ancient tea tree (Photographed by Sun Qian)

I. Taxonomy and Distribution

The wireworm belongs to the order Coleoptera, superfamily Elateroidea, family Elateridae, and is an important pest in China. It is named the wireworm because its larva is slender and needle-like. Over 600 species of wireworms are known in China. Dominant species include the channelled click beetle (Plenomus canaliculatus), narrow-necked click beetle (Agriotes subvittatus), brown-banded click beetle (Melanotus caudex), and broad-backed click beetle (Selatosomus latus). They are distributed in various provinces and regions across China, including Yunnan, Guizhou, Shanxi, Gansu, Hebei, Liaoning, Xinjiang, Taiwan, Zhejiang, Fujian, and Hunan. Wireworms are omnivorous pests with a wide range of hosts, including tea trees, cereals, tubers, legumes, ginseng, sugarcane, bamboo shoots, and others.

II. Morphological Characteristics

1. Adult: Wireworms are small to large, measuring 2-80 mm in length. Their bodies are elongated and cylindrical, tapering towards the end, slightly flattened, and mostly dark-colored, with some brightly colored ones having metallic luster or patterns. The head is small and transversely embedded in the prothorax. The antennae consist of 11-12 segments, mostly serrate. The posterior angles of the prothorax form sharp spines, and the prothoracic ventral plate is long and narrow, extending into the groove of the mesothoracic ventral plate (Figure 6). There is a movable joint between the prothorax and mesothorax. When captured, they continuously make a “nodding” motion through the joint formed by the posterior protrusion of the prothoracic ventral plate and the mesothoracic ventral fossa, hence the name click beetle.

Figure 6: Adult wireworm (Photographed by Shu Jinping)

2. Egg: Wireworm eggs are round or elliptical, 0.5-1.0 mm in length, and milky white. 3. Larva: Wireworm larvae are slender and cylindrical, slightly flattened. Initially, they are white (Figure 3), undergoing 9-15 molts, gradually turning yellowish-brown to reddish-brown. The head and last abdominal segment are particularly hard. The antennae consist of three segments. The dorsal splitting line is shaped like an inverted convex character. The thoracic legs have four segments, and the abdomen has ten segments with a tail projection. The spiracles are of the bimodal type (Figure 5). 4. Pupa: Wireworm pupae measure 5-30 mm in length. Initially, they are pale green or milky white, later becoming darker in color.

III. Damage and Habits

Wireworms primarily damage plant stems and roots through their larvae. In tea gardens, especially in older tea trees, since wireworms burrow deep into the trunk, they are difficult to control due to their hidden nature and long lifecycle. The larvae cluster and feed on the main trunk near the ground and roots, creating tunnels and producing a large amount of wood shavings (Figures 2 and 4), leading to damage to the phloem and xylem. This obstructs the transport of nutrients between the above-ground and underground parts of the tea tree, causing yellowing and thinning of the leaves. The wounds caused by wireworms also allow pathogens to invade, causing various damages to the tea tree. Severe infestations can lead to the death of the tea tree, resulting in significant economic losses. Adult wireworms can damage tea tree flowers, buds, or bark.

In China, it takes 2-5 years for wireworms to complete one generation. Mature larvae pupate in August to September, with a pupal period of 16-20 days. They emerge as adults in early September but do not emerge from the soil until the following year, overwintering in the soil. They mate and lay eggs in the soil in March to April of the following year, hatching around early May. The larvae start damaging the tea tree from the roots upwards, feeding on the