The Red Borer is one serious pest of tea and often damage young plants in Sri Lanka, Malaysia, Taiwan, Indonesia, India and it causes considerable damage in Assam. Another species Z.leuconotum causes damage in Japan. The larva of the borer (Zeuzera coffeae Nietner) bores into the tea stem, mostly one or two year’s old wood. The leaves of the affected branch wither and eventually die. The larva usually tunnels downwards, eating away woody tissues. In due course, it passes into the thicker stems, and in young tea plants the tunnel may extend down to the tap root. At various intervals, during the course of tunneling, circular holes are cut out through which excreta in the form of pinkish pellets is ejected piling up on the ground below.
In Upper Assam and China, the oecophorid stem borer Casmara patrona Meyrick occasionally damages tea stem. The hepialid borer, Sahyadrassus malabaricus Moore is an occasional pest in South India. In China and Georgia Parametriotes theae Kusnetsov damages tender stems.
The scolytid shot-hole borer Euwallacea fornicates Eichoff is a highly destructive pest in South India and Sri Lanka. It occurs in Indonesia and Taiwan also. The borer is also well known pest of tea in mid and low elevation areas of South India and occasional pest in N.E. India.
In N.E. India and Bangladesh several species of Cockchaffer grubs, particularlyHolotrichia impressaBurm occasionally cause serious harm to young plants. The grub attacks the roots of the young plants below three years of age. Clonal plants are more affected than the seedling plants. The larva eats away the bark in the collar region of the plants just below the soil surface either in ring or in patches resulting in the death of the plant.
Extensive callus growth develops when the bark is eaten away in girdle and the plants die. However, the damage is healed up by callus growth when the debarking is less extensive and does not completely girdle the tap root. The major part of the damage is caused during June-August.
Cockchafer Grub Infestation and the Grubs
Carpenter moth (Teregra quadrangular) is a serious pest especially of young tea in Central Africa. Caterpillars feed on the bark and ring bark the branches resulting in calluses and knots. Ring barking of young plants may result in death of plants.
Stem eating beetles in small number are found on tea bushes in N.E.India as well as in Darjeeling causing damage to tender stem from March to October. It includes orange beetle (Diapromorpha melanopus Lecord) and green beetle (Chrysolamra flavipes Jacoby).
Brown cricket (Brachytrypes portentosus) is one of the most destructive pests in nursery. It lives in burrows in the soil. At night, it comes out of the burrows and cuts off the leaves and tender shoots and often drags them into the burrows in the soil. It also cuts the roots of the young plants and the nursery seedlings
A number of termite species are responsible for considerable damage to mature teas. Two species of termites cause damage to the tea plants. They are:
(a) Live wood eating termites (Microcerotermes sp.) and
(b) Scavenging termites (Odontotermes sp.)
Live wood eating termites attack the living, dead and rotting wood of the tea bushes under covered earthruns.They first attack the dead wood before going to healthy tissues. Fine channels are then excavated along the heartwood and these are progressively enlarged and eventually the stems are hollowed out leaving a thin layer of wood and the bark. The attack gradually spreads to other branches causing destruction of the frame and main stem and ultimately resulting in the death of the bush.
The scavenging termites have their nests in mounds or underground and reach their target under covered earthruns. Normally, they feed on the dead, dying and crumbly wood and rarely attack healthy wood but the removal of the dead tissues leads to further death of the adjoining healthy tissues.
Continued removal of such tissues leads to the formation of cavities and hollows in the stems and with the increasing damage the cavities and hollows are enlarged. The cavities and hollows are in due course filled up with earth carried by the termites.
Another species of scavenging termites, the mound building termites (Odontotermes assamensis) construct mounds of 3-4 feet high and cover considerable space and alter the physical and chemical properties of the soil. The nature of damage is similar to that of scavenging termites.