**3. Insect pests of tea and management problems**

Tea is produced from the young foliage, i.e. young leaves and a bud, and foliage production is increased by seasonal pruning which enhances the leaf cover. The major pests of the crop are those associated with the young foliage. The most important insect pest groups are the folivores (chewing) and sap suckers of the young tender leaves, buds and stems (sucking pest), which damage the most economic part of tea plant that is processed in tea industry for making the tea. These pests cause substantial loss in yield to the tea industry.

In India, different management practices are followed to protect the tea crop against different insect pest groups. Most of the plantations are managed conventionally i.e. using different organosynthetic insecticides, whereas some organic plantations use plant- and animal-based herbal and microbial insecticides. In conventional tea plantations, organo-synthetic insecti‐ cides of different functional groups such as organochlorines, organophosphates, synthetic pyrethroids (SPs) and neonicotinoids (NNs) are regularly used throughout the year to control the invasion of different insect pest groups (sucking, folivores and others) [8]. The use of insecticide is cost-effective to planters and a major concern for the environmental degradation due to contamination as well as in resurgence of primary pests [6], outbreak of secondary pests [9], development of insecticide resistance [10, 11], including undesirable residues in made tea [12]. Regular spraying of insecticides leads to the development of higher level of tolerance or resistance to insecticides in many insects [11, 13].

**Sl. no. Name of the pests Nature of damage Family: Order** 1. *Andraca bipunctata* Walk. Bunch caterpillar Folivores Bombycidae: Lep. 2. *Eterusia magnifica* Butl. Red slug caterpillar Folivores Zygaenidae: Lep. 3. *Buzura suppressaria* Guen. Looper caterpillar Folivores Geometridae: Lep. 4. *Hyposidra talaca, H. infixaria* Walk. Black inch worm Folivores Geometridae: Lep. 6. *Lymantria albulunata* Mre. Sungma caterpillar Folivores Lymantridae: Lep. 7. *Gracillaria theivora* Walsh. Tea leaf roller Folivores Gracilariidae: Lep. 8 *Homona coffearia* Nietner Tea tortrix Folivores Torticidae:Lep. 9. *Laspeyresia leucostoma* Mayer. Flushworm Folivores Eucosmidae: Lep. 10. *Holotrichia impressa* Burm. Cockchafer grubs Root of young tea Scarabaeidae: Col. 11. *Serica assamensis* Brenske Leaf-eating cockchafer Leaf eater Scarabaeidae: Col. 12. *Asticus chrysochlorus* Wied. Large green weevil Leaf eater Curculionidae: Col. 13. *Agromyzidae* (Bigot) Meij Tea leaf miner Leaf eater Agromyzidae: Dip. 14. *Microtermes* spp. Live wood-eating termite Stem and root eater Termitidae: Iso. 15. *Odontotermes* sp. Scavenging termite Stem and root eater Termitidae: Iso. 16. *Helopeltis theivora* Waterhouse Tea mosquito bug Leaf sucker Miridae: Hem. 17. *Empoasca flavescens* Fabr. Tea greenfly/tea jassid Leaf sucker Jassidae: Hem. 18. *Toxoptera aurantii* Boyer de Fons. Tea aphid Leaf sucker Aphididae: Hem. 19. *Scirtothrips dorsalis* Hood Yellow tea thrips Leaf and bud sucker Thripidae: Thy.

21 *Oligonychus coffeae* Nietner Red spider mite Leaf sucker Tetranychidae: Aca. 22. *Brevipalpus phoenicis* Geijskes Scarlet mite Leaf sucker Tenuipalpidae: Aca.

Tea is produced from the young foliage, i.e. young leaves and a bud, and foliage production is increased by seasonal pruning which enhances the leaf cover. The major pests of the crop are those associated with the young foliage. The most important insect pest groups are the folivores (chewing) and sap suckers of the young tender leaves, buds and stems (sucking pest), which damage the most economic part of tea plant that is processed in tea industry for making

In India, different management practices are followed to protect the tea crop against different insect pest groups. Most of the plantations are managed conventionally i.e. using different

Common thrips Leaf and bud sucker Thripidae: Thy.

20. *Mycterothrips (Teaniothrips) setiventris*

**Table 1.** Major insect and mite pests that occur on tea in India.

**3. Insect pests of tea and management problems**

the tea. These pests cause substantial loss in yield to the tea industry.

Bagnall

350 Insecticides Resistance

From the early forties onwards, dichlorodiphenyltrichloroethane (DDT) (organochlorine) was regularly used to manage the infestation of *H. theivora,* the major sucking pest in Northeast India [14]. In 1968, endosulfan (cyclodiene: organochlorine) was introduced in the tea planta‐ tions of the Dooars region of West Bengal, India, in the form of thiodan 35 EC [15]. Currently, in different conventional tea plantations of tea-growing regions of India, cypermethrin, deltamethrin, quinalphos, monocrotophos, chlorpyriphos, imidacloprid, etc. are extensively used during cropping season to control insect pests [16–18].

Recently, a number of insecticides have been found to be ineffective in controlling the insect and mite pests in different tea-growing regions of India [8]. The development of resistance to different classes of insecticides is one of the causes for persistence and resurgence of insect pests on tea crop [8, 19–21]. A major concern in managing the major insect pests of tea is its high potential to develop resistance rapidly to regularly used insecticides [11]. Continuous and repeated exposure to different classes of insecticides for many years, in addition to their high reproductive potential, short life cycle and numerous annual generations, has limited the management of major pests of tea [11]. Recently, there are reports on the development of resistance to many commonly used synthetic insecticides and consequent failure in controlling many tea pests [10, 22–26]. Such failures are already known in case of organochlorines (OCs), organophosphorus (OP) and synthetic pyrethroid (SP) insecticides and more recently for the newer compound such as neonicotinoids [19–21, 26]. The development of resistance in *H. theivora* populations to different classes of insecticides has been in the range of 1.47–62.99-fold for males and 1.25–62.82-fold for females in Northeast India [19]. Relative toxicity to commonly used insecticides has been observed to vary in *H. theivora* populations from Jorhat, Assam [20], Darjeeling [27], and from sub-Himalayan Dooars region of Northeast India [28]. LC50 values of insecticides, when compared with the field dose against *H. theivora* recommended by TRA (Tea Research Association, Tocklai, Assam, India), revealed a pronounced shift in the level of susceptibility of *H. theivora* to all insecticides except acephate [20–21].

For the management of other sucking insects such as yellow tea thrips, *S. dorsalis,* insecticides are also used in conventional tea plantations*.* In tea ecosystem, control failure and the devel‐ opment of biochemical resistance have been reported in *S.* dorsalis [11, 24]. In India, *S. dorsalis* populations have developed a high degree of resistance to a range of organochlorine (DDT, BHC and endosulfan), organophosphate (acephate, dimethoate, phosalone, methyl-Odemeton and triazophos) and carbamate insecticide (carbaryl) in chili ecosystem [31]. *S. dorsalis* has also developed a high degree of resistance to various insecticides, viz. monocro‐ tophos, acephate, dimethoate, phosalone, carbaryl and triazophos [32]. Recently, several insecticides have been tested on *S. dorsalis* in chili ecosystem in USA and found limited success with chlorfenpyr, spinosad and imidacloprid [33, 34]. The performance of novaluron, aba‐ mectin, spiromesifen, cyfluthrin, methiocarb and azadirachtin failed to provide effective control of this pest [35].

Similarly, in another emerging sucking insect pest of tea, tea greenfly, *E. flavescens*, repeated management failure and biochemical insecticide resistance in tea ecosystem from Northeast India have been reported [11, 24]. In China, chemical insecticides including fenvalerate, cyfluthin, cypermethrin and imidacloprid are sprayed to control the leafhoppers as frequently as seven times annually or even more frequently [36–37]. A high level of resistance against many insecticides has been reported in related species, *E. vitis* [38]. The resistance to thiame‐ thoxam was highest and to cyperemethrin was lowest in *E. vitis.* Recently, in Fujian province of China, a regional diversity of resistance to eight insecticides in *E. vitis* has been reported in tea ecosystem with higher resistance level to bifenthrin, acetamiprid, imidacloprid, cartap and chlorfenapyr [39].

A high level of insecticide resistance in folivores, such as black hairy caterpillar, bunch caterpillar, looper pest complex (*Hyposidra talaca, H. infixaria, Buzura suppressaria, Eturesia magnifica*) and in termite of tea ecosystem, has been reported with reduced susceptibility against different insecticides.

Detoxification of insecticides is an important toxicokinetic mechanism for insect pests to tolerate regularly applied insecticides [8, 40–42]. Susceptibility levels against insecticides change mainly due to metabolic detoxification of the insecticides through the induction of some detoxifying enzymes under the stress of different management practices [43–45].

Generally, three principal enzymes, general esterases (GEs), glutathione S-transferases (GSTs) and cytochrome P450-mediated monooxygenases (CYP450s), are involved in the process of metabolic detoxification of insecticides [41]. Estimation of the activities of these metabolic defence-related detoxifying enzymes gives information on the level of tolerance/resistance of the insect pest population to insecticides and is a useful tool in monitoring the tolerance/ resistance to insecticides at population level of the pest. The early detection of metabolic threats related to tolerance/resistance to insecticides in pest specimens is of crucial importance for devising pest control techniques that would minimize the development of tolerant/resistant forms and prevent any undesirable wastage of insecticide, money and manpower.
