Development of formulations from Samadera indica Gaetrn. for the management of leaf feeding pests in snake gourd(Trichosanthes anguina L.)

Abstract

The study entitled ‘Development of formulations from Samadera indica Gaetrn. for the management of leaf feeding pests in snake gourd (Trichosanthes anguina L.)’ was carried out in the Department of Agricultural Entomology, College of Agriculture, Vellayani and at Council of Scientific and Industrial Research – National Institute for Interdisciplinary Science and Technology (CSIR-NIIST), Thiruvananthapuram during 2018 to 2021. Objectives of the study were exploration of anti-insect properties of bark and seeds of S. indica, identification of bioactive compounds in the effective extract, development of suitable formulations and field evaluation of the same against pumpkin caterpillar, Diaphania indica Saund and epilachna beetle, Henosepilachna septima (Dieke). Estimation of lethal doses viz., LD50 and LD90 of bark and seed extracts by probit dose analysis showed that LD50 of bark extract in hexane, acetone, ethanol extract and aqueous extract were 1.66, 1.03, 1.51 and 2.38% respectively against D. indica and 2.17, 1.95, 1.68 and 2.49% respectively against H. septima. Meanwhile, LD90 values were 6.49, 7.05, 5.24 and 7.90% respectively against D. indica and 6.82, 6.60, 6.17 and 7.85% against H. septima. In the case of seed extract, LD50 values were 1.79, 0.59, 1.03 and 1.54% respectively against D. indica and 1.63, 0.83, 1.60 and 2.43% against H. septima. LD90 values were 6.99, 5.17, 7.05 and 9.17% against D. indica and 9.53, 5.27, 7.94 and 9.02% against H. septima. Results of in vitro studies on antifeedant effect of S. indica bark extracts against D. indica showed that ethanol extract @ 5.24% exhibited the highest leaf protection of 62.79 per cent at 72 Hours After Treatment (HAT). In the case of H. septima, ethanol extract @ 6.17% resulted in 65.00 per cent leaf protection. Regarding insecticidal effect, ethanol extract @ 5.24% resulted in 93.33 per cent mortality of second instar larvae of D. indica. Meanwhile, in grubs of H. septima, ethanol extract @ 6.17% inflicted 91.67 per cent mortality. Insecticidal effect of both the extracts was found to be statistically on par with chemical check (Malathion 50 EC 0.1%). With regard to insect biology, there was increase in larval duration (15.00 days), pupal duration (5.33 days), reduction in pupal weight (0.19 g) and reduction in adult longevity (4.33 days) in D. indica, whereas in control, larval and pupal period were 9.67 and 2.67 days each, pupal weight was 0.31 g and longevity of adults was 7.67 days. Similar trend was observed in H. septima. Among various extracts from S. indica seeds, acetone extract @ 5.17% resulted in the highest leaf protection of 74.41 per cent in D. indica and acetone extract @ 5.27% exhibited 71.79 per cent leaf protection in H. septima. With respect to insecticidal effect, acetone extract @ 5.17 and 5.27% each caused 86.67 per cent mortality in D. indica and H. septima respectively. Considering biology of the insects, there was prolongation in larval period to 17.00 days, pupal period to 8.67 days, reduction in pupal weight to 0.25 g and reduction in adult longevity to 6.33 days in D. indica as against larval period of 12.67 days, pupal period of 5.33 days, pupal weight of 0.35 g and adult longevity of 7.67 days in control. Similar was the trend with H. septima also. A comparison between LD50 and LD90 of bark and seed extracts pointed out that seed extract contained more potent compounds with insecticidal properties. Hence, seed extract was taken for further studies. Chromatographic fractions from acetone extract of seeds @ 5% exhibited mean leaf protection of 91.83 per cent in D. indica and 85.71 per cent in H. septima. Meanwhile, there was mortality of 73.33 per cent in both the pests. Analysis of chromatographic fractions revealed the presence of quassinoids viz., samaderin A, samaderin B, samaderin C and cedronin in the seed extract. Molecular structures were elucidated to confirm the identity of the compounds. Two formulations of S. indica seed extract were prepared by mixing seed extract, emulsifier and distilled water in different proportions. Formulation A contained acetone extract of S. indica seed, tween 80 and distilled water in 15: 5: 80 ratio. Formulation B was prepared by mixing seed extract of S. indica in acetone, tween 80 and span 80 (1: 1) and distilled water in 15: 5: 80 ratio. Both the formulations A and B were equally effective against D. indica and H. septima under in vitro conditions, with 80.00 per cent mortality each at 72 HAT. Safety evaluation on beneficial insects indicated that formulation A @ 1% resulted in 30.00 per cent mortality in honey bee after 24 HAT, while in A. taragamae, it was 23.33 per cent. Furthermore, both the formulations were stable under normal room temperature for six months. Formulation A @ 1% recorded 71.67 to 80.00 per cent mortality in D. indica and H. septima from the day of preparation till sixth month of storage. Meanwhile, formulation B @ 1% resulted mean percentage mortality of 70.00 and 75.00 per cent in D. indica and H. septima. Considering the insecticidal effect under in vitro conditions and environmental feasibility, formulation A was chosen for in vivo studies. Field experiment was carried out to test the efficacy of the botanical in comparison with biopesticide and chemical at Instructional Farm, Vellayani in snake gourd (variety Kaumudi). Formulation A @ 2% was evaluated for its efficacy against D. indica and H. septima at vegetative stage and 50 per cent flowering stage. Observations were taken on pest population and percentage of damaged leaves. It can be deduced that formulation A @ 2% was as effective as neemazal @ 0.2% as evident with reduction in pest population at vegetative and 50 per cent flowering stage of the crop. With regard to reduction in leaf damage, formulation A @ 2% excelled equally as neemazal @ 0.2% at vegetative stage. The study revealed that both bark and seed extracts of S. indica exhibited feeding deterrence, insecticidal properties and caused adverse effects in the biology of D. indica and H. septima. Anti-insect properties are more prevalent in the seeds and they contained the bioactive compounds samaderins A, B, C and cedronin. Formulations containing acetone extract of S. indica seeds, tween 80 and distilled water (15: 5: 80) @ 1 and 2% each were effective against both the pests under in vitro and in vivo conditions respectively and were stable for a period of six months under room temperature. Hence, it can be concluded that formulations from S. indica can be considered as safer botanical insecticides in this era of organic farming.