Antifeedant and growth regulatory activity of Sphagneticola trilobata(L) Pruski on tobacco caterpiller, Spodoptera litura (Fab)(Lepidoptera: noctuidae)

Abstract

One of the most important aspects of agriculture is pest management. Pesticides used in the past produced a variety of environmental problems, including ecological imbalances, soil fertility loss, and marine life degradation. Conventional pesticides have also been linked to a number of significant and detrimental effects on human and animal health, including severe malignancies, neurological diseases, hormone disruptions, and reproductive troubles. Botanical pesticides are found to be an effective alternative to conventional pesticides for pest management. Sphagneticola trilobata (L.) Pruski, is an herb included in the Asteraceae and is well known for its medicinal properties, information about its bioactivity against insects is very less. Hence, in this study we evaluated the antifeedant and growth regulatory activity of various extract of Sphagneticola trilobata against Spodoptera litura. Dried and powdered S. trilobata plant materials were sequentially extracted with hexane and methanol followed by concentrated in vacuo in a rotary evaporator at a lower temperature to obtain crude extracts of S. trilobata. Hexane extracts of aerial parts and roots were named as SP1 and SP3 and methanol extract of aerial parts and roots were named as SP2 and SP4. The yield of methanol extract of aerial parts (5.67% w/w) was higher followed by methanol extract of roots (2.32% w/w), hexane extract of aerial parts (1.96% w/w) and hexane extract of roots (1.23% w/w) The antifeedant activity of various extracts of Sphagneticola trilobata tested in nochoice leaf disc bioassay revealed that methanol extract of aerial parts of S. trilobata had the maximum antifeedant activity of 52.10 per cent at 0.1 per cent of the extract against S. litura after 24h of feeding. Compared to aerial extracts, root extracts were less active against S. litura. At lower concentrations, the antifeedant activity of all the extract were not much prominent and are not statistically significant. The antifeedant activity of all the extract increased in 48h experiment except for 0.1 per cent concentration. The decreasing order of antifeedancy of four extracts was SP2>SP1>SP4>SP3. ii Similar results were recorded in the choice method of bioassay of extracts against S. litura. Maximum antifeedant activity of 46.65 per cent was obtained for methanol extract of aerial parts (SP2) after 24h of feeding. At lowest concentrations of 0.005, 0.01 and 0.03 per cent none of the extracts exhibited significant difference in activity. Increasing concentration beyond 0.03 per cent had a significant effect on antifeedancy in the choice method. As similar to the no-choice method, reduced activity was recorded after 48h of feeding. Maximum antifeedant activity of 38.81 per cent was recorded for SP2 after 48h of feeding. Similar to the no-choice method, root extracts exhibited a low level of activity against S. litura. Insect growth regulatory activity of various extracts was evaluated by diet incorporation method against five-day old larvae of S. litura. A maximum larval weight reduction of 31.4 per cent was recorded for SP4 at 0.1 per cent of the extract. A significant increase in larval duration compared to control was recorded for SP2 extracts at higher concentrations. Similar to larval weight reduction, a dose-dependent pupal weight reduction was recorded for SP1 (29.57 per cent at 0.1 per cent of the extract). Compared to the other three extracts, pupal weight reduction was very less for SP3. Pupal duration increased to a maximum period of 13.54 days at 0.1 per cent of SP4. Observations on abnormal pupae were not significant for any of the extracts. No larval mortality could be obtained with any of the treatments. A maximum of 16.7 per cent larval pupal intermediates was recorded for SP4 at the highest dose, but it was not significantly different from other treatments. Similar to larval mortality, no pupal adult intermediates were recorded for any of the extracts. Maximum pupal mortality of 41.00 per cent was recorded at 0.1 per cent of SP1, and it was significantly different from other treatments. For all the extracts, pupal mortality was dose-dependent. Minimum adult emergence was noticed for SP1 at 0.1 per cent of the extract. GC-MS/MS and LC-MS/MS analysis of active fractions revealed that more phytochemicals are present in aerial parts than roots. The higher activity of aerial parts might be due to the presence bioactive compounds like andrographolide, artemisin, iii genistein and taxifolin. Most of the chemicals identified were derivatives of steroids, terpenoids and flavonoids. The study results indicate that methanol extract of aerial parts of S. trilobata has strong antifeedant activity against S. litura. All other extracts were relatively less active against S. litura. Insect growth regulatory activity was maximum for hexane extract of aerial parts. All the extracts adversely affected the growth and devolvement of S. litura. The absence of larval mortality indicates that all the extracts have less contact toxicity.