Andrographolide based biopesticide for the management of pest complex of vegetable cowpea Vigna unguiculata (L.) Walp

Abstract

The present study entitled ‘Andrographolide based biopesticide for the management of pest complex of vegetable cowpea Vigna unguiculata (L.) Walp’. was carried out at Department of Entomology, College of Agriculture, Vellayani, during 2019-2023 with an objective to develop and standardize an “andrographolide” based biopesticide formulation against pests of vegetable cowpea V. unguiculata and its insecticidal and antifeedant effect on developmental stages of pests and natural enemy. Extraction and isolation of the bioactive compound from Andrographis paniculata, were isolated using the modified procedure of Pundarikakshudu et al., 2016 and resulting compound was further confirmed to be andrographolide through Fourier-transform infrared spectroscopy (FTIR) and Liquid chromatography-mass spectrometry (LC-MS) analysis. The effectiveness of isolated andrographolide based compound were studied on cowpea aphids (Aphis craccivora) and spotted pod borer (Maruca vitrata). The LC50 and LC90 were calculated at 24 hours after treatment and recorded concentration of 2064.51ppm and 3206.52ppm, respectively. A significant mortality was observed in the second and third instar larvae of M. vitrata. Studies were conducted to develop formulations showing stable emulsions (bloom test) and five combinations were found to be forming stable emulsions. Stable five combination were Andrographolide (70%) + Neem oil (20%) + Triton X 100 (10%), Andrographolide (70%) + Pungam oil (20%) + Triton X 100 (10%), Andrographolide (60%) + castor oil (30%) + Tween 80 (10%), Andrographolide (60%) + Palm oil (30%) + Tween 80 (10%) and Andrographolide (60%) + sunflower oil (30%) + Tween 20 (10%) and effectiveness of these five combinations were tested against A. craccivora at various concentration (3, 5 and 7%). The treatments Andrographolide (70%) + Neem oil (20%) + Triton X 100 (10%) (Formulation A) and Andrographolide (70%) + Pungam oil (20%) + Triton X 100 (10%) (Formulation B) were found to be superior among the other treatments. The invitro evaluation of formulations A and B against A. craccivora revealed that the LC50 values of formulations A and B were 1.51 and 1.42% respectively and the LC90 values of formulations A and B were recorded as 4.52 and 4.40%. Another study conducted to evaluate the safety of predatory 198 coccinellids, Cheilomenes sexmaculata and the result revealed that the formulations A and B exhibited a relatively safer profile with minimal adverse effects on the predatory coccinellid even at higher concentrations, as mortality rates remained below 50%. Observations on the orientation behaviour of M. vitrata and L. boeticus larvae revealed a significant decrease in mean larval orientation towards treated floral buds and pods with various concentrations of formulations A and B and this highlights the deterrent impact of the formulations on larval orientation. Antifeedant activity of formulations A and B towards 3rd instar larvae of M. vitrata and L. boeticus at 7% of the formulations showed extremely antifeedant activity followed by 5 and 3% of formulations. Larvae fed with treated flowers exhibited a reduction in size compared to the control. Both M. vitrata and L. boeticus larvae exhibited a shortened larval duration and extended pupal period when provided with different concentration of formulations A and B. Considering the adult emergence rate of M. vitrata minimum emergence recorded in 7% of formulation B (31.25%), which on par with 7% of formulation A (37.5%). Conversely, no significant difference in adult emergence was observed between treatments in L. boeticus. The antifeedant effect on pod bug, R. pedestris using different concentrations of formulations A and B recorded significant feeding deterrence effect. All the treatments showed significant antifeedant activity at 12 HAT, and at 7% of both formulations A and B recorded more than 95% of antifeedant activity, and were found to be on par with 5% of formulation B. The assessment of the repellent activity of formulations A and B against A. craccivora revealed a significant repellent activity on aphids and maximum repellency was recorded at 7% of both formulation A and B (98 and 96 per cent, respectively) at 24 HAT. The efficacy of formulations A and B at various concentrations on egg hatching and larval development in L. boeticus and R. pedestris were studied and the result revealed concentration-dependent effects of formulations A and B on the egg hatchability and developmental stages of both L. boeticus and R. pedestris, with lower hatching rates and prolonged incubation periods observed at higher concentrations compared to the untreated control.