Eco-friendly biosynthesis of TiO2 nanoparticles using Desmostachya bipinnata extract: Larvicidal and pupicidal potential against Aedes aegypti and Spodoptera litura and acute toxicity in non-target organisms.

The resistance to insecticides among insects, including mosquitoes and agricultural pests, and the impact of these compounds' environmental risks and health issues have motivated the proposition of eco-friendly alternatives. Thus, we aimed to explore the potential use of Desmostachya bipinnata for the biosynthesis of TiO2NPs and evaluate their larvicidal and pupicidal activity of target (Aedes aegypti and Spodoptera litura) and acute toxicity in non-target organisms (Toxorhynchites splendens and Eisenia fetida), at distinct concentrations, after 24 h of exposure. The characterization of the biosynthesized TiO2NPs was carried out by FT-IR, XRD, SEM, and EDX analysis. Under the UV-vis spectrum analysis, a sharp peak was recorded at 200 to 800 nm, which indicated the production of TiO2NPs by the plant extract. The SEM analysis revealed that the synthesized TiO2NPs were spherical with a diameter of 36.4 nm and were detected in the XRD spectrum analysis related to the TiO2NPs. The highest percentage of mortality recorded at 900 µg/mL was 96 % and 94 % in the 2nd instar of A. aegypti and S. litura larvae, respectively, and exhibited the LC50 and LC90 values 5 of 458.79 and 531.01 µg/mL, respectively. The biosynthesized TiO2NPs showed concentration-dependent increased pupal lethality for both A. aegypti and S. litura. We also observed increased detoxification enzyme activity (α esterase, ß esterase, and glutathione-S-transferase) of A. aegypti and S. litura exposed to different concentrations of biosynthesized TiO2NPs as histopathological changes in the midgut region of these animals. On the other hand, the mortality rate of non-target organisms (T. splendens and E. fetida) was lower when exposed to TiO2NPs, compared to the high lethality induced by synthetic pesticides (cypermethrin and monocrotophos for E. fetida; and cypermethrin and temphos for T. splendens). Thus, our study provides pioneering evidence on the potential use of D. bipinnata-mediated TiO2NPs for controlling mosquito vectors and agricultural pest management.

Effects of phytocompound Precocene 1 on the expression and functionality of the P450 gene in λ-cyhalothrin-resistant Spodoptera litura (Fab.).

Spodoptera litura (Fabricius) is an agriculturally significant polyphagous insect pest that has evolved a high level of resistance to conventional insecticides. A dietary assay was used in this work to assess the resilience of field populations of S. litura to λ-cyhalothrin. Analysis of the function and expression of the cytochrome P450 gene was used to test the sensitivity of S. litura larvae to sub-lethal concentrations of the insecticidal plant chemical Precocene 1, both by itself and in combination with λ-cyhalothrin. The activity of esterase enzymes (α and ß) was found to decrease 48 h post treatment with Precocene 1. The activity of GST enzyme and cytochrome P450 increased with Precocene 1 treatment post 48 h, however. Expression studies revealed the modulation by Precocene 1 of cytochrome P450 genes, CYP4M16, CYP4M15, CYP4S8V4, CYP4G31, and CYP4L10. While CYP4M16 expression was stimulated the most by the synergistic Precocene 1 + λ-cyhalothrin treatment, expression of CYP4G31 was the most down-regulated by Precocene 1 exposure. Hence, it is evident that λ-cyhalothrin-resistant pest populations are still sensitive to Precocene 1 at a sublethal concentration that is nevertheless capable of hindering their development. Precocene 1 can therefore be considered a potent candidate for the effective management of insecticide-resilient S. litura.

Efficacy of Precocene I from Desmosstachya bipinnata as an Effective Bioactive Molecules against the Spodoptera litura Fab. and Its Impact on Eisenia fetida Savigny.

The sustainability of agroecosystems are maintained with agro-chemicals. However, after more than 80 years of intensive use, many pests and pathogens have developed resistance to the currently used chemistries. Thus, we explored the isolation and bioactivity of a chemical compound, Precocene I, isolated from the perennial grass, Desmosstachya bipinnata (L.) Stapf. Fractions produced from chloroform extractions showed suppressive activity on larvae of Spodoptera litura (Lepidoptera: Noctuidae), the Oriental armyworm. Column chromatography analyses identified Precocene I confirmed using FTIR, HPLC and NMR techniques. The bioactivity of the plant-extracted Dp-Precocene I was compared to a commercially produced Precocene I standard. The percentage of mortality observed in insects fed on plant tissue treated with 60 ppm Db-Precocene I was 97, 87 and 81, respectively, for the second, third and fourth instar larvae. The LC50 value of third instars was 23.2 ppm. The percentages of survival, pupation, fecundity and egg hatch were altered at sub-lethal concentrations of Db-Precocene I (2, 4, 6 and 8 ppm, sprays on castor leaves). The observed effects were negatively correlated with concentration, with a decrease in effects as concentrations increased. Distinct changes in feeding activity and damage to gut tissues were observed upon histological examination of S. litura larvae after the ingestion of Db-Precocene I treatments. Comparative analyses of mortality on a non-target organism, the earthworm, Eisenia fetida, at equal concentrations of Precocene I and two chemical pesticides (cypermethrin and monocrotophos) produced mortality only with the chemical pesticide treatments. These results of Db-Precocene I as a highly active bioactive compound support further research to develop production from the grass D. bipinnata as an affordable resource for Precocene-I-based insecticides.

Developmental response of Spodoptera litura Fab in response to plant extract of Desmostachya bipinnata (L.) and its effect on non-target organism, earthworm (Eisenia fetida).

Impact of chloroform extract of Desmostachya bipinnata was evaluated on armyworm Spodoptera litura (Lepidoptera: Noctuidae). The chloroform extract of D. bipinnata was subjected to GC-MS analysis to elucidate the vital 12 compounds. The mortality of S. litura was tested at four different concentrations viz., 0.5, 1.0, 1.5, and 2.0 %, which exhibited a dose-dependent response. Mortality was significant at a concentration of 2%. Accrued LC50 (lethal concentration) value was 0.15%. The developmental duration of larva and pupa was significantly increased in all treatments. Reduction in weight of pupae in treated groups was noticed and was compared with control. Longevity of S. litura decreased in all tested treatments and being most significant at concentrations of 1.5 and 2%. Simultaneous reduction in fecundity of S. litura was observed. Pathological changes were noticed in the mid gut of S. litura at concentrations of 1 and 1.5%. No significant impacts on earthworm were observed. The results of the present study revealed that chloroform extract from D. bipinnata, an old-world perennial grass, shown effective bio-pesticidal activity against S. litura, an important agricultural pest.

Toxic effect of essential oil and its compounds isolated from Sphaeranthus amaranthoides Burm. f. against dengue mosquito vector Aedes aegypti Linn.

Aedes aegypti is a major mosquito vector that can transfer many deadly diseases such as dengue, chikungunya, Zika, and yellow fever viruses. Due to the developing resistance among the vector populations by the application of chemical insecticides, alternative eco-friendly vector management strategies are being focused. In this aspect, the present study was carried out to evaluate the mosquitocidal potentials of essential oil of Sphaeranthus amaranthoides (EO-Sa). EO-Sa was found to be effective against Ae. aegypti mosquito vector by exhibiting significant larvicidal, adulticidal and repellent activities. GCMS analysis of EO-Sa revealed the presence of Carvone as the major component (peak area of 89.7%). The larvicidal bioassays performed revealed that the second instar larvae were relatively more susceptible (94.32% mortality) to EO-Sa treatments (75 ppm), LC50, 20.38 ppm.The sub lethal treatment concentration (20 ppm) significantly affected the oviposition, fecundity and morphology of Ae. aegypti. At sub lethal treatment concentration, EO-Sa down regulated α- and ß carboxylesterase and up regulated the GST and CYP450 level of third and fourth instar larvae. Thus the present results illustrates that EO-Sa can deliver a durable larvicidal, repellent and adulticidal activity against Ae. aegypti in an effective and eco-friendly manner.