Pests of medicinal plants in Kerala

Abstract

dicinal plants are known to Indian traditional healers since time immemorial. Kerala is known for its rich biodiversity of medicinal plants that support both traditional and modern healthcare practices. When cultivated in large areas, medicinal plants are much more prone to pest attacks, which cause considerable damage. Since limited information was available on pests of medicinal plants, the present study entitled "Pests of medicinal plants in Kerala" was conducted to document the pests associated with medicinal plants in the region, to generate DNA barcodes of cryptic species collected and to study the biology and population dynamics of indigo psyllid, Euphaleropsis isitis, an important pest of Indigofera tinctoria. Purposive sampling surveys were carried out in 32 locations across 10 districts of Kerala, covering 15 agroecological units distributed among five agroecological zones. The study documented 55 pest species associated with 10 selected medicinal plants viz., I. tinctoria, Ocimum spp., Coleus aromaticus, Plectranthus vettiveroides, Withania somnifera, Plumbago spp., Piper longum, Kaempferia galanga, Pseudarthria viscida and Desmodium gangeticum. Additionally, 17 species were recorded from 13 medicinal plants viz., Pogostemon cablin, Aristolochia indica, Tylophora indica, Asparagus racemosus, Thespesia populnea, Strobilanthes cusia, Saraca asoca, Tephrosia purpurea, Ruta graveolens, Aegle marmelos, Calotropis gigantea, Hibiscus sp. and Helicteres isora. Of the total pests collected, 31 were under the order Hemiptera, 24 Lepidoptera, 10 Coleoptera, two Orthoptera, one mite species and snail. This study revealed 40 new host associations and a new distributional record for Sphenoptera konbirensis (Coleoptera: Buprestidae). Barcoding of seven insect pests viz., Orphanostigma abruptalis, Bemisia tabaci, Aleurothrixus trachoides, Lygaeus sp., Cochlochila bullita, Icerya aegyptiaca and Plumbago leaf miner was done. For this, genomic DNA was isolated, mitochondrial cytochrome oxidase I (mtCO1) was amplified and sequenced. The in-silico analysis revealed that O. abruptalis, Lygaeus sp., B. tabaci, and A. trachoides showed more than 98 per cent similarity, whereas C. bullita, I. aegyptiaca and Plumbago leaf miner showed less than 93 per cent similarity with the available sequences in the NCBI database. The sequences were submitted to NCBI to obtain accession numbers and to BOLD for generating species specific barcodes. The indigo psyllid, E. isitis is a major pest infesting I. tinctoria. There were no comprehensive studies on the biology and factors affecting the population build-up of E. isitis on indigo plant. This study represented the first detailed investigation on the biology and population dynamics of the indigo psyllid. The biology was studied in the laboratory at ambient conditions to document its morphology and developmental duration. Eggs were elongate oval, pale yellow and later turned black, with an incubation period of 6 ± 0.77 days. The dorsoventrally flattened nymphs passed through five instars, completing development in 15.5 ± 1.75 days. The total life cycle lasted for approximately 21.5 days. Adults were small, with slender antennae, forewings marked with black spots and variable abdominal colouration. Females (2.62 ± 0.127 mm long, 0.92 ± 0.050 mm wide) were larger than males (2.24 ± 0.077 mm long, 0.88 ± 0.062 mm wide). Mean longevity was 17.4 ± 3.55 days in females and 16.4 ± 3.83 days in males. Females laid an average of 209.9 ± 61.83 eggs over a period of 13.1 ± 3.20 days with a brief pre-oviposition period of 2.2 ± 0.4 days. The population of different life stages of E. isitis, viz., egg, nymph and adult of psyllid, were recorded from September 2024 to August 2025 and correlated with the weekly average of one-week prior weather data. The population was comparatively higher during July-August. The abundant population of nymphs and adults during the rainy season could be attributed to the lush growth of the plant stimulated by rainfall. Egg did not show correlation with any weather factors. Nymph had positive significant correlation with rainfall. The adult exhibited a significant negative correlation with maximum temperature and bright sunshine hours. A significant positive correlation was observed between evening humidity and adult population, while rainfall displayed a highly significant positive correlation. A further study extending over 2-3 years is required to assess population dynamics and their correlation with weather factors.