Management of insect pests of Gloriosa superba L., the state flower of Tamil Nadu

Glory lily, the state flower of Tamil Nadu is being commercially cultivated in Tamil Nadu. Field experiments were conducted to study the arthropod biodiversity and to develop eco-friendly management strategies. Results of the studies on insect biodiversity in gloriosa ecosystem revealed that the lepidopteran pests viz., lily caterpillar, Polytela gloriosae, semilooper, Plusia signata and tobacco cutworm, Spodoptera litura and a sucking pest viz., Thrips tabaci were recorded to be the major pests. Early instar lily caterpillars fed on chlorophyll of the leaves but the later instars fed voraciously leaving only the hard stem of the plant resulting in complete devastation. Eggs were small, round and dorsoventrally flattened. Egg period varied from 3 to 6 days. The larval period lasted for 14 to 18 days and the larvae underwent five moults to become pupa. The eggs of tobacco cutworm were small, round and were laid in clusters of several hundreds, usually on leaf surfaces. The egg period varied from 3 to 4 days. The larval period varied from 15 to 18 days with five larval instars. Pupation took place inside the soil. Eggs of semilooper were laid singly on underside of the leaves. The egg period varied from 2 to 3 days. Larval period lasted for 14 to 17 days with five instars. Thrips infesting Gloriosa superba was identified as Thrips tabaci. Body of the adult thrips was recorded to be 1.0 to 1.2 mm long and yellowish-grey to dark-grey in color. Wings have single longitudinal vein with a fringe of hairs. Dark blotches are observed on the thorax and abdomen. Female laid 30 to 80 whitish eggs. There were two nymphal stages that lasted up to 14 days, after which the larva entered quiescence. This pre-pupal stage (1-2 days) was followed by the pupal stage. Adult females lived for 10 to 13 days. These thrips were identified as vectors in transmitting necrosis, a viral disease. Virus infected plants developed a bronze or purple discoloration. Leaves curled downwards and were distorted. Affected leaves wilted and died. Dark streaks appeared on stems near the growing point, led to death of the plant. Based on the results of field experiments conducted for the management of lepidopteran pests of G. superba, flavonoids were adjudged as the best alternative to the chemical pesticides in gloriosa eco-system and for the management of thrips and gloriosa necrosis, foliar application of fipronil at 1.25 mL L^-1 was recommended.