Impact of caffeic acid on growth, development and biochemical physiology of insect pest, Spodoptera litura (Fabricius).

The tobacco cutworm, Spodoptera litura (Fabricius) is a serious cosmopolitan pest that attacks several economically important crops such as maize, sorghum, chickpea, pigeon pea, cotton, tobacco and sunflower. It has developed resistance to most pesticides resulting in its continual outbreak. The effect of caffeic acid on second instar larvae of S. litura was evaluated by carrying out bioassays, nutritional assays, immune assays and biochemical assays with phenolic acids. Bioassays carried out with second instar larvae of S. litura showed growth inhibiting effects of various concentrations (5 ppm, 25 ppm, 125 ppm, 625 ppm and 3125 ppm) of caffeic acid on S. litura in comparison to control. A significant increase in mortality as well as an increased development time was observed with increase in the concentration of caffeic acid. A decrease in nutritional indices, including relative growth rate (RGR), relative consumption rate (RCR), efficiency of conversion of ingested food (ECI), efficiency of conversion of digested food (ECD), and approximate digestibility (AD), indicated that dietary caffeic acid also negatively impacted the nutritional physiology of S. litura larvae. Caffeic acid has a significant impact on the immunological response of S. litura larvae. As the concentration of caffeic acid increased, the overall number of hemocytes decreased. Enzymatic assays revealed a significant increase in antioxidant enzymes when S. litura larvae were given an artificial diet containing LC50 concentration of phenolic acid for an interval of 24, 48, 72 and 96 h. The levels of oxidative stress markers (hydrogen peroxide, protein carbonyl and lipid peroxide) were also significantly enhanced in S. litura larvae after treatment with phenolic acid. According to our study, caffeic acid can be employed as a substitute for traditional insecticides to reduce the population of S. litura.

Effect of daidzein on growth, development and biochemical physiology of insect pest, Spodoptera litura (Fabricius).

Anti- insecticidal potential of daidzein was studied by feeding second instar larvae of Spodoptera litura (Fabricius) on artificial diet incorporated with different concentrations (5 ppm, 25 ppm, 125 ppm, 625 ppm) of diadzein. Results revealed high larval mortality, prolongation of pupal and total developmental period of the larvae treated with diadzein. Anti-nutritional/post ingestive toxicity of diadzein was also revealed by the decrease in the nutritional indices such as relative growth rate (RGR), relative consumption rate (RCR), efficiency of conversion of digested food (ECD), efficiency of conversion of ingested food (ECI) and approximate digestibility (AD). The suppression of immune function due to decline in the total hemocytes count was also observed in treated S. litura larvae. Profiles of detoxifying enzymes viz. superoxide dismutases (SOD), catalase (CAT), ascorbate peroxidases (APOX) and glutathione S-transferase (GST) were also significantly increased with diadzein treatment. The hydrogen peroxide content (H2O2), lipid peroxide content (LP) and protein carbonyl content were also significantly enhanced in the treated larvae thus, indicating oxidative stress in the insect. Our findings suggest that daidzein can be used as the alternative to conventional pesticides for controlling S. litura population.

Effect of gallic acid on the larvae of Spodoptera litura and its parasitoid Bracon hebetor.

The antibiosis effect of gallic acid on Spodoptera litura F. (Lepidoptera: Noctuidae) and its parasitoid evaluated by feeding six days old larvae on artificial diet incorporated with different concentrations (5 ppm, 25 ppm, 125 ppm, 625 ppm, 3125 ppm) of the phenolic compound revealed higher concentration (LC50) of gallic acid had a negative impact on the survival and physiology of S. litura and its parasitoid Bracon hebetor (Say) (Hymenoptera:Braconidae). The mortality of S. litura larvae was increased whereas adult emergence declined with increasing concentration of gallic acid. The developmental period was delayed significantly and all the nutritional indices were reduced significantly with increase in concentration. Higher concentration (LC50) of gallic acid adversely affected egg hatching, larval mortality, adult emergence and total development period of B. hebetor. At lower concentration (LC30) the effect on B. hebetor adults and larvae was non-significant with respect to control. Gene expression for the enzymes viz., Superoxide dismutase, Glutathione peroxidase, Peroxidase, Esterases and Glutathione S transferases increased while the total hemocyte count of S. litura larvae decreased with treatment. Our findings suggest that gallic acid even at lower concentration (LC30) can impair the growth of S. litura larvae without causing any significant harm to its parasitoid B. hebetor and has immense potential to be used as biopesticides.