Citation: Pokharel, S.S.; Yu, H.; Fang, W.; Parajulee, M.N.; Chen, F. Intercropping Cover Crops for a Vital Ecosystem Service: A Review of the Biocontrol of Insect Pests in Tea Agroecosystems. Plants 2023, 12, 2361. https://doi.org/10.3390/plants 12122361 Academic Editor: Vincent G.M. Bus Received: 18 April 2023 Revised: 9 June 2023 Accepted: 15 June 2023 Published: 18 June 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). plants Review Intercropping Cover Crops for a Vital Ecosystem Service: A Review of the Biocontrol of Insect Pests in Tea Agroecosystems Sabin Saurav Pokharel 1 , Han Yu 2 , Wanping Fang 3 , Megha N. Parajulee 4 and Fajun Chen 1, * 1 Departmentof Entomology, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China; pokharelsabin93@gmail.com 2 Department of Forest Genetics and Breeding, College of Forestry, Nanjing Forestry University, Nanjing 210037, China; yuhan00107@163.com 3 Department of Tea Science, College of Horticulture, Nanjing Agricultural University, Nanjing 210095, China; fangwp@njau.edu.cn 4 Texas A&M AgriLife Research and Extension Center, 1102 East Drew Street, Lubbock, TX 79403, USA; megha.parajulee@ag.tamu.edu * Correspondence: fajunchen@njau.edu.cn Abstract: The intercropping of cover crops has been adopted in several agroecosystems, including tea agroecosystems, which promotes ecological intensification. Prior studies have shown that growing cover crops in tea plantations provided different ecological services, including the biocontrol of pests. Cover crops enrich soil nutrients, reduce soil erosion, suppress weeds and insect pests, and increase the abundance of natural enemies (predators and parasitoids). We have reviewed the potential cover crops that can be incorporated into the tea agroecosystem, particularly emphasizing the ecological services of cover crops in pest control. Cover crops were categorized into cereals (buckwheat, sorghum), legumes (guar, cowpea, tephrosia, hairy indigo, and sunn hemp), aromatic plants (lavender, marigold, basil, and semen cassiae), and others (maize, mountain pepper, white clover, round-leaf cassia, and creeping indigo). Legumes and aromatic plants are the most potent cover crop species that can be intercropped in monoculture tea plantations due to their exceptional benefits. These cover crop species improve crop diversity and help with atmospheric nitrogen fixation, including with the emission of functional plant volatiles, which enhances the diversity and abundance of natural enemies, thereby assisting in the biocontrol of tea insect pests. The vital ecological services rendered by cover crops to monoculture tea plantations, including regarding the prevalent natural enemies and their pivotal role in the biocontrol of insect pests in the tea plantation, have also been reviewed. Climate-resilient crops (sorghum, cowpea) and volatile blends emitting aromatic plants (semen cassiae, marigold, flemingia) are recommended as cover crops that can be intercropped in tea plantations. These recommended cover crop species attract diverse natural enemies and suppress major tea pests (tea green leaf hopper, white flies, tea aphids, and mirid bugs). It is presumed that the incorporation of cover crops within the rows of tea plantations will be a promising strategy for mitigating pest attacks via the conservation biological control, thereby increasing tea yield and conserving agrobiodiversity. Furthermore, a cropping system with intercropped cover crop species would be environmentally benign and offer the opportunity to increase natural enemy abundance, delaying pest colonization and/or preventing pest outbreaks for pest management sustainability. Keywords: tea agroecosystem; cover crops; ecosystem services; biological control; natural enemies; environmentally benign; sustainable pest management 1. Introduction Tea, Camellia sinensis (L.) Kuntze, is an important economic crop used to produce the world’s oldest and most popular caffeine-containing beverage of immense cultural and Plants 2023, 12, 2361. https://doi.org/10.3390/plants12122361 https://www.mdpi.com/journal/plants