Pests of ornamental plants in commercial horticultural nurseries of Kerala

Abstract

In Kerala, commercial horticultural nurseries serve as the cradle of ornamental plant trade. The incidence of pests is one of the major challenges faced by ornamental plants in nurseries. However, literature pertaining to pests of ornamental plants in horticultural nurseries of Kerala is scanty. Hence, the present study entitled "Pests of ornamental plants in commercial horticultural nurseries of Kerala", was carried out to document the insects and non-insect pests associated with different ornamental plants. Purposive sampling surveys were carried out in 50 nurseries from 11 districts of Kerala. Insect and non-insect pests infesting 43 flowering ornamentals and 17 ornamental foliage plants were collected. The pests were preserved as per standard protocols and got identified by experts in the relevant taxa. Among the documented pests, sucking pests predominated (69%) followed by defoliators (15%), non-insect pests (11%), flower feeders (4%) and stem borers (1%). The study recorded 50 species of sucking insect pests in two orders viz., Hemiptera and Thysanoptera. Hemipteran pests include 28 species of scale insects (Pseudococcidae- mealybugs (6), Coccidae- soft scales (11), Diaspididae- armoured scales (7), Monophlebidae-giant scales (3), Ortheziidae- ensign scales (1)), eight species of aphids (Aphididae), four species of whiteflies (Aleyrodidae) and one species of lacewing bug (Tingidae). Thysanopteran pests include and nine species of thrips in two families viz., Thripidae (7) and Phlaeothripidae (2). The defoliator pests include five species of caterpillars (Noctuidae (2), Nymphalidae (1), Pyralidae (1), and Sphingidae (1)), three species of leaf-feeding beetles (Curculionidae (2) and Chrysomelidae (1)) and three species of grasshoppers (Acrididae). Three species of flower feeders which includes one species of bud-boring caterpillar (Noctuidae) and two species of flower beetles (Scarabaeidae (1) and Chrysomelidae (1)) as well as one species of stem borer (Cerambycidae) were documented. The non-insect pests documented include six species of mites (Tetranychidae (5) and Eriophyidae (1)) and two species of snails (one Ariophantidae and one unidentified species of aquatic snail) Among the mealybugs documented, Ferrisia virgata recorded a wider host range of seven ornamental plants species, while the highest infestation was recorded by Phenacoccus solenopsis on hibiscus. The scale insect Ceroplastes rubens was recorded on four plant species, while the per cent pest infestation was found to be higher for Coccus viridis on ixora plants. Among aphids, the highest pest infestation was noticed in Aphis gossypii infesting Ixora, while among whiteflies, Bemisia tabaci recorded the highest infestation on Euphorbia pulcherrima. Of the thrips recorded, Thrips florum infesting rose showed the highest infestation percentage in nurseries. Spodoptera litura had been the polyphagous defoliator surveyed and found to infest nine species of ornamental plants. Among the defoliators, higher infestation was recorded by Polytela gloriosa on Hymenocallis littoralis, Myllocerus subfasciatus on Melastoma sp. and Nisotra basselae on hibiscus. The primary polyphagous flower feeder causing severe economic damage to the ornamental plants recorded during this study was Popillia japonica. The stem borer, Cleonaria bicolor, whose grubs hollowed out the tender stems while adults scraped the midribs, veins and stem, had been documented from Ixora coccinea. The mite species Tetranychus gloveri exhibited a wide host range of five ornamental plants. The snail Macrochlamys indica was found to feed on many species of ornamental plants, but the infestation was severe on Canna indica. Even though the nursery owners were reluctant to reveal the pest management strategies, the common cultural practices adopted by them were: cleaning and proper monitoring at timely intervals, greenhouse protective structures to reduce the incidence of pests, intermittent mist irrigation to manage the excess temperature rise under polyhouse conditions, innovative irrigation practices like Ebb and flow system that helped in maintaining the plant's health and soil-less potting media like fibre enriched giffy that reduced the incidence of soil pests. Mechanical measures involved hand-picking in the case of caterpillars and pruning of the old or pest-affected branches to reduce the spread of pests like thrips or whiteflies. Yellow and blue sticky traps were used to manage the population of sucking pests in nurseries. Biological measures involved the use of Neem oil garlic emulsion (2%), Nimbecidine (Azadirachtin 0.03%), entomopathogens like Lecanicillium lecani (Vertilac) against aphids and whiteflies and Beuveria bassiana against lepidopteran pests. The common pesticides used in nurseries include Thiamethoxam (Actara), Fipronil 5% SC (Agadi), Dimethoate 30%EC, Chlorantraniliprole 18.5%SC (Coragen), Bifenthrin 10% EC(Boxer)and Quinalphos 25% EC(Ekalux). Molecular characterization of nine sucking insect pests was performed by isolation of genomic DNA and amplification of mitochondrial cytochrome oxidase one (mtCO1) locus using specific primers. The sequencing of PCR products and in silico analysis of three species of aphids, two species of each of thrips, mealybugs, and scales, were carried out. All the sequences showed a similarity between 95-100 percent with the sequence in the NCBI database and hence agreed with the morphological identification. The sequences were submitted to the NCBI database and uploaded to Barcode of Life Data Systems (BOLD), and specific barcodes were generated. The study documented 73 species of pests infesting 60 species of ornamental plants and the existing pest management practices in horticultural nurseries. Further studies on biology, seasonal incidence, and geographical distribution of major pests of ornamental plants have to be carried out to evolve specific, and environment-friendly pest management strategies for horticultural nurseries in the state.