Detection and molecular characterization of soft scale insect, Megapulvinaria maxima (Green) (Hemiptera: Coccidae) infesting Gymnema sylvestre (Retz.) R.Br. ex Sm. from India

Abstract

Gymnema sylvestre (Retz.) R. Br. ex Sm is a vital medicinal plant effective in treatment of Diabetes mellitus. The soft scale, Megapulvinaria maxima (Green) (Hemiptera: Coccidae), has emerged as a significant pest infesting Gymnema sylvestre in the semi-arid region of India. A random survey revealed infestation on leaves, stems, and fruits, by both nymphs and adults extracting plant sap and secreting excess honeydew. This honeydew adversely impacts leaf quality which is essential for bio-molecule extraction. Early pest detection is crucial for effective management, but the precise morphological identification of scale insects poses challenges. Utilizing morphological keys and sequencing the Cytochrome c oxidase subunit I (COI) gene (GenBank No. OR602704), we identified the scale insects as M. maxima. Evolutionary divergence studies and phylogenetic analysis indicated no divergence with the Republic of Korea isolate (MK543913), while with the isolate of the accession number, MW450949 highest evolutionary divergence was exhibited (0.72%). The isolates (KP189890) and (KP189893) from China showed less association with the study isolate compared to other populations. The severity of incidence peaked during the 48th and 45th standard meteorological weeks (SMW) in 2019–20 and 2020–21, reaching severity levels of 3.67 and 3.56, respectively. In both years, morning relative humidity showed a significantly positive correlation (r = 0.152 and 0.364*). These findings offer valuable insights for early pest detection and formulating effective management strategies. To the best of our knowledge, this is the first comprehensive study of M. maxima affecting the medicinal herb G. sylvestre in India and globally.