New Record of Tetranychus kanzawai (Acari: Tetranychidae) on Cassava in India¹

Cassava (Manihot esculenta Crantz) ranks sixth in global annual production and third as an important source of calories (FAOSTAT 2019). In India, it is cultivated mainly in the states of Tamil Nadu, Kerala, and Andhra Pradesh, accounting for 96% of the total production in India (Government of India, Horticulture Statistics at a Glance 2018).

A major problem in cassava cultivation is the incidence of pests like mites, mealybugs, whiteflies, hornworms, lace bugs, thrips, and burrower bugs. Nearly 50 species of mites have been reported from cassava including Mononychellus mcgregori (Flechtmann and Baker), Neotetranychus lek (Flechtmann), Oligonychus thelytokus (Gutierrez), Tetranychus marianae (McGregor), Tetranychus yusti (McGregor), Tetranychus urticae (Koch), Eutetranychus africanus (Tucker), Oligonychus biharensis (Hirst), Tetranychus cinnabarinus (Boisduval), Tetranychus neocaledonicus (Andre), Tetranychus truncatus (Ehara), Tetranychus kanzawai (Kishida), and Eutetranychus orientalis (Klein) from Asia (Graziosi et al. 2016, Plant Arch. 19: 2810–2814).

During February 2023, sudden yellowing and drying of the leaves were noticed in cassava fields cultivated in two localities of Pananchery, Thrissur District, Kerala, India (global positioning system coordinates: 10°33′22″N, 76°18′6″E and 10°33′30″N, 76°17′52″E), extending to an area of approximately 2 ha where cassava had been cultivated for >20 yr. H.B. was contacted by the agricultural extension officer of the Panchayat, and diagnostic visits were made to the site. Symptoms of chlorosis, drying, and defoliation were noted in the cassava fields. Under magnification, large numbers of spider mites in various life stages (e.g., eggs, nymphs, and adults), their molted exuviae, and webbing were observed on the abaxial surface of the cassava leaves.

Mite-infested leaf samples were collected randomly from 15 plants in each location. Three leaves were collected from each plant from the upper, middle, and lower areas of the plant canopy. Leaf samples were placed individually in polythene bags, sealed, labeled, and transported to the laboratory for identification. In the laboratory, the leaves were observed under a microscope (LeicaEZ4HD) to record mite population. On average, our mite count yielded 22.44 eggs/cm² and 24.36 active stages/cm² of leaf area were recorded. A single gravid female mite was released on individual mulberry (Morus sp.) leaves placed on a wet sponge in separate plastic trays to establish a colony in the laboratory (Wang et al. 2015, Syst. Appl. Acarol. 20: 579–590).

The male and female mites (F1 generation) from the colony were slide mounted in Hoyer’s medium for morphologic characterization and species determination. The key taxonomic characters of T. kanzawai (Fig. 1) were observed as follows:

View Figure

• Download as Powerpoint
• Download Figure

Female: Tarsus I with sockets of four tactile setae proximal to the socket of proximal duplex setae (Fig. 1A). Dorsal body setae are longer than the intervals between their bases (Fig. 1B). Hysterososma with longitudinal striae between the third pair of dorsocentrals (e1) and between the fourth pair of dorsocentrals (f1); a diamond-shaped figure is formed between these two pairs of setae (Fig. 1C). Dorsal striae with lobes (Fig. 1D).

Male: Empodia I–II each with an obvious dorsal spur; empodia I clawlike (uncinate), empodia II–IV with proximoventral hairs, long and free (Fig. 1E). Aedeagal knob one-third to the length of the dorsal margin of shaft, with a rounded anterior projection and an acute posterior projection, dorsal surface convex. Knob and shaft axis almost parallel (Fig. 1F) (Sreenivasa et al. 2021, Spider mite fauna of India, AINPAA, pp. 68).

In addition, the homology analysis of the mitochondrial cytochrome C oxidase I gene sequence with deoxyribonucleic acid extracted from 10 adult female mites using the C-TAB method in the National Center for Biotechnology Information (NCBI)-BLAST (http://www.ncbi.nlm.nih.gov) showed 99.31% similarity with the sequence of T. kanzawai (accession KU870626.1) in the NCBI database, thus further confirming the species identity through molecular identification. The sequence generated in this study was submitted to NCBI GenBank under the accession number OR534585.

In India, T. kanzawai was first recorded from Delhi on Morus sp. (Nassar and Swaraj 1984, Orient. Insects 15: 333–396.). Later, it was recorded on French bean (Phaseolus vulgaris L.), amaranthus (Amaranthus spp.), and papaya (Carica papaya L.) in Karnataka, and on apple (Malus domestica Borkh.) in Ludhiana (AINPAA Prog. Res. 2018). It also has been reported as one of the most common red spider mite species in Southeast Asia on cassava (Sanjaya et al. 2013, Arthropods 2: 208–215). However, this is the first report of (a) T. kanzawai from Kerala and (b) cassava as a new host record in India.