INTRODUCTION Sorghum, a grain crop used for both human and animal consumption, is the sixth most dryland crop. Sorghum and other coarse grains have historically been the central part of the diet of rural and lower-income semi-urban households in India. India ranks sixth in total sorghum output with 4.8 million tonnes, with Tamil Nadu producing 4.27 lakh tonnes (INDIASTAT, 2021). Sorghum, popularly known as "cholam," is grown in Tamil Nadu for both grain and fodder purposes. From the time of emergence until the late stages of grain filling, more than 150 species of insects have been identified as sorghum pests (Harris, 1995). Biodiversity is a function of the total number of taxa present, the evenness with which they are dispersed (either within species or within families), and the relationship between richness and evenness, or diversity (Ludwig and Reynolds, 1988). Insect diversity accounts for more than 80% of the diversity of species on the planet, making them a common choice for ecological indicators (Samways, 1993). Studies on the status pertaining to insect diversity in sorghum ecosystems are considerably poor. Therefore, an attempt was made to assess the diversity and abundance of sorghum insect pests and natural enemies in sorghum ecosystem to have a better understanding of the selection pressure to which the crop is subjected to. MATERIALS AND METHODS Arthropod diversity in sorghum was studied at the Millet Breeding Station, Tamil Nadu Agricultural University (TNAU), Coimbatore during Rabi 2021 (11°01'01.8"N 76°55'50.5"E; 420 MSL). Sorghum variety Co 32 was cultivated in an area of around 1.4 acre with standard package of practices. Arthropod sampling was undertaken at weekly intervals from 7 days after germination to harvest spanning a total of 110 days. Different sampling methods were employed viz net sweeping, pitfall traps and light traps. Net sweeping was carried out by walking diagonally inside the field in the morning and evening hours. Five places were chosen randomly and 15-20 net sweeps were done at each place to collect insects. Pitfall traps were kept at 7 different sites randomly in the field and collections were made at weekly intervals. Light trap was set up twice per week between 7 pm and 11 pm and the samples were collected the following morning. The insect samples collected were preserved using dry and wet preservation techniques (stored in 70 percent ethanol) for identification (Schauff, 1986). Arthropod diversity was assessed using various diversity indices that included Shannon-Wiener index (Shannon & Weiner, 1949) for species diversity, Simpson’s diversity index (Simpson, 1949) for species dominance, Margalef’s index (Margalef, 1958) for species richness and Equitability J index (Magurran, 1987) for species evenness. RESULTS AND DISCUSSION A total of 3,361 individuals were collected which comprised of 46 species falling under of 30 families with the most dominant ones being the Hemiptera. The detailed list of the species is provided in Table 1. The most abundant insect order was Hemiptera comprising 77.09% of the total population. Within the order, Peregrinus maidis was the most abundant species noticed in sorghum. Chelliah and Basheer (1965) reported that this pest may even cause death of the plant in severe cases. Pentatomid insects like Nezara viridula, Dolycoris indicus and Menida versicolor (Reddy and Davies 1979; Prabhakar et al., 1981) have been reported damaging sorghum panicles. Pyrilla spp. also has been reported as a potential pest. So far, many mirid bugs have been reported attacking sorghum of which Calocoris angustatus was found to be a key pest in southern parts of India (Sharma and Lopez 1990). Hoppers like Nephotettix spp. (Kalaisekar et al., 2017), Cofana spp. and Proutista moesta (Caasi-Lit 2018) were reported infesting sorghum and maize. The second most abundant order, Coleoptera, made up 9.10% of all insect species. Many of coleopteran species were natural enemies of pests infesting sorghum. Cheilomenes sexmaculata, Micraspis spp. And Chilocorus melas were reported as natural enemies in sorghum ecosystem (Sherlin et al., 2019). El-Gepaly (2019) also reported the following four species as predators of sorghum: Coccinella transversalis, Scymnus spp., Chrysoperla spp. And Paederus fuscipes. Kalaisekar et al. (2017) reported Altica spp. and Myllocerus spp. as pests infesting sorghum and millets in India. Monolepta signata and Aulocophora foveicollis were reported as defoliators of sorghum (Reddy and Davies 1979). The record of Oxyrachis tarandus, a pest of pigeon pea may be due to the presence of a pulse crop in the vicinity. Hymenoptera was the next abundant order with 6.34% of total population. Tarihoran et al. (2020) reported hymenoptera as the most abundant order in sorghum ecosystem in Indonesia. He has reported that, the relative density value is high in the family Formicidae. Srivastava and Bryson (1956) reported Solenopsis spp. as the serious pest of planted sorghum seeds. Apis cerana indica and Ropalidia marginata were observed as pollinator and predator respectively. Diptera with 5.21% relative abundance has the most important pests such as Contarinia sorghicola and Atherigona soccata (Reddy and Davies 1979). Lepidopteran pests such as Chilo partellus (Young 1970) and Spodoptera frugiperda (Wilde 2006) were also recorded. Despite having a significant economic impact, these pests were not well represented in the collection. This may be caused by environmental factors like the weather, season, or type of light source, among others. Mohyuddin (1970) reported a list of parasitoids attacking graminaceous stem borers which includes Braconidae and Tachinidae. Camponotus compressus, Euantissa spp., Orthotylus spp. and long legged bug were reported as predators by Sherlin et al. (2019). There are previous records of soil dwelling insects such as earwig by Hassan (1987) and sorghum root weevil, Apinocis deplanatus recorded by Bryson (1941) attacking sorghum and sugarcane. Atractomorpha crenulata was also found attacking millets. There are also reports of other acridids attacking sorghum (Reddy and Davies 1979). However, there are no reports of Plecia spp. and Dictyoptera in sorghum ecosystem. Other orders including Neuroptera, Mantodea, Dictyoptera and Dermaptera contributes less than one percent of total population. The Shannon–Wiener diversity index, Simpson’s diversity index, Margalef’s richness index and Pielou’s evenness were used as heterogeneity measures for computing diversity (Table 2). It could be observed that Shannon-Wiener index was the maximum for Coleoptera (2.201). Since each individual in this order belongs to a different species, their diversity index is the larger than others. The dominance as measured by Simpson’s dominance index has values ranging from 0.12 to 0.75. Thus, the order Hemiptera (0.7514) had the maximum dominance index value and also it is the order with the most number of families. Hemiptera also has highest number of individual species count thus making it dominant over other orders. The value of Margalef index is different for all the Orders; maximum in Coleoptera (1.922) indicating high level of species richness, while least in Orthoptera (0.572) indicating low level of species richness. Pielou’s evenness values range from 0 to 1.0, with 1.0 representing complete evenness (Magurran 2004). The order Lepidoptera (0.9012) with the Pielou’s evenness value nearing 1 is considered to be having a more balanced distribution of species in the community. These results are in agreement with those reported by Duffield (1995) who interpreted higher insect abundance to edaphic and locally prevailing ecological factors. Wang et al. (2000) stated that the reduction in species richness was mainly caused by biotic and abiotic factors; therefore, distribution of insect pests and predatory species in the selected study area seemed to be dependent on climatic factors such as temperature, relative humidity, rainfall and wind.