Toxicity of Bioactive Molecule Andrographolide against Spodoptera litura Fab and Its Binding Potential with Detoxifying Enzyme Cytochrome P450.

Spodoptera litura Fab. is a polyphagous pest causing damage to many agriculture crops leading to yield loss. Recurrent usage of synthetic pesticides to control this pest has resulted in resistance development. Plant-derived diterpenoid compound andrographolide was isolated from the leaves of Andrographis paniculata. It was analysed by gas chromatography-mass spectroscopy and quantified by HPLC. Nutritional indices and digestive enzymatic profile were evaluated. Third, fourth and fifth instar larvae were treated with different concentrations of andrographolide. At 3, 6 and 9 ppm-treated concentrations the larvae showed decreased RGR, RCR, ECI, ECD values with adverse increase in AD. The digestive enzymes were significantly inhibited when compared with control. Conspicuously, andrographolide showed pronounced mortality of S. litura by inhibition of enzyme secretion and intake of food. The binding ability of andrographolide with CYTP450 showed high affinity with low binding energy. Andrographolide has the potential to be exploited as a biocontrol agent against S. litura as an eco-friendly pesticide.

Target and non-target toxicity of botanical insecticide derived from Couroupita guianensis L. flower against generalist herbivore, Spodoptera litura Fab. and an earthworm, Eisenia foetida Savigny.

Botanical insecticides may provide alternatives to synthetic insecticides for controlling Spodoptera litura (F.) and they are target specific, biodegradable, and harmless to mammals. Eight natural chemical compounds with larvicidal activity were identified from fraction F6 of C. guianensis flower extract. Probit analysis of 95% confidence level exposed an LC50 of 223ppm against S. litura third instar larvae. The growth and development of S. litura was affected in sub-lethal concentrations of fraction F6 (50, 100, 150 and 200ppm) compared to controls. Similarly nutritional indices values decreased significantly compared to controls. Fraction F6 also damaged the gut epithelial layer and brush border membrane (BBM). This study also resolved the effects of toxicity to non-target earthworm treated with fraction F6 and chemical pesticides (monotrophos and cypermethrin) and the results showed that fraction F6 had no harmful effect on E. fetida. Further, fraction F6 was eluted and sub fractions F6c (50ppm) showed high mortality against S. litura third instar larvae. Octacosane from fraction F6c was established and confirmed using IR spectrum and HPLC. The time of retention of fraction F6c was confirmed with the octacosane standard. Fraction F6 of C. guianensis extract caused dose-dependent mortality towards S. litura. Octacosane in fraction F6c was establish to be the prominent chemical compound associated with causing mortality but other compounds present in the fraction F6 were shown to be associated with changes in development of S. litura at low dosages. S. litura at low dosage. Therefore, these findings suggest that octacosane may be one of the major insecticidal compounds affecting S. litura survival.

Female sex pheromone of the Gelechiid moth Scrobipalpa salinella (Zeller).

The sex pheromone system of Scrobipalpa salinella (Zeller), an important pest of the halophyte Salicornia europaea in the tidal salt marshes, was studied. Z3-12:OAc and Z5-12:OAc were identified from both female pheromone glands and female emissions, but in quite different ratios. Field trapping tests demonstrated that Z3-12:OAc and Z5-12:OAc are essential for optimal attraction of male moths, and a 100:5 blend found in gland extracts is significantly more attractive to males than a 100:50 ratio similar to that found in SPME samples. Small amounts of E3-12:OAc and Z5-14:OAc also were present in pheromone gland extracts. A blend of E3-12:OAc with Z3-12:OAc attracted a few males, but was not as attractive as the binary blend of Z3-12:OAc and Z5-12:OAc. Moreover, addition of E3-12:OAc did not affect captures of males to the primary binary blend. Another glandular component, Z5-14:OAc, had no behavioral activity in field bioassays. Therefore, a synthetic mixture of Z3-12:OAc and Z5-12:OAc in a 100:5 ratio can be used as an effective tool for monitoring and control of this species.

Toxicity and behavioral effect of 3beta,24,25-trihydroxycycloartane and beddomei lactone on the rice leaffolder Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae).

Treatment of Dysoxylum pure triterpenes 3beta,24,25-trihydroxycycloartane and beddomei lactone to the rice leaffolder (RLF), Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae), resulted in prolonged larval duration and reduced larval weight. In leaf cut choice assay and topical application experiments, beddomei lactone and 3beta,24,25-trihydroxycycloartaneto showed strong antifeedant and growth inhibitor activity against fourth instar larvae of C. medinalis. Also average leaf consumption was decreased (89%) by the treatment of the two terpinoids when compared with controls. Number of eggs laid by the female (fecundity) was decreased and oviposition deterrence index was increased due to the treatment. This result further shows that the pure triterpenes of Dysoxylum act as both an antifeedant and chronic toxin to the rice leaffolder larvae.

Toxicity and physiological effects of neem pesticides applied to rice on the Nilaparvata lugens Stål, the brown planthopper.

The effects of two different neem products (Parker Oil and Neema) on mortality, food consumption and survival of the brown planthopper, Nilaparvata lugens Stål (BPH) (Homoptera: Delphacidae) were investigated. The LC(50) (3.45 ml/L for nymph and 4.42 ml/L for adult in Parker Oil treatment; 4.18 ml/L for nymph and 5.63 ml/L for adult in Neema treatment) and LC(90) (8.72 ml/L for nymph and 11.1 ml/L for adult in Parker Oil treatment; 9.84 ml/L for nymph and 13.07 ml/L for adult in Neema treatment) were identified by probit analysis. The LC(90) (equal to recommended dose) was applied in the rice field. The effective concentration of both Parker Oil and Neema took more than 48 h to kill 80% of the N. lugens. Fourth instar nymph and adult female N. lugens were caged on rice plants and exposed to a series (both LC(50) and LC(90)) of neem concentrations. Nymph and adult female N. lugens that were chronically exposed to neem pesticides showed immediate mortality after application in laboratory experiment. The quantity of food ingested and assimilated by N. lugens on neem-treated rice plants was significantly less than on control rice plants. The results clearly indicate the neem-based pesticide (Parker Oil and Neema), containing low lethal concentration, can be used effectively to inhibit the growth and survival of N. lugens.

The toxicity and physiological effect of goniothalamin, a styryl-pyrone, on the generalist herbivore, Spodoptera exigua Hübner.

Efficacy of Goniothalamin a styryl-pyrone isolated from Goniothalamus wightii Hook.f. and Thoms, against beet armyworm, Spodoptera exigua (Hübner), populations was determined under laboratory condition. The experiments were carried out with concentrations of 5, 10, 15 and 30 ppm in an artificial diet and compared with control insects. Laboratory bioassay showed that the goniothalamin had a strong effect on food utilization, moulting and gut histology. The food consumption and conversion of ingested and digested food to body matter decreased with increasing pyrone concentration. The antifeedant activity was also observed in larvae of S. exigua. The treated third instar larvae exhibited mortality in a dose dependent manner. At 5, 10, 15 and 30 ppm/insect, the pyrone gave 23%, 45% 63% and 100% mortality respectively. The larvae of S. exigua gained significantly less weight until pupation in the 10 and 15 ppm pyrone concentrations. Duration of larval period was also affected after treatment with pyrone. The metamorphosis was delayed with additional moulting (7th instar) after treatment with 10 and 15 ppm of goniothalamin, the percentage of larvae successfully moulted into progressive instars was significantly decreased with an increase in pyrone concentrations. The effects of goniothalamin on midgut ultrastructure of third instar larvae of S. exigua were investigated by using light microscopy. Cross sections of the midgut showed that the epithelial cells were destroyed. Significant damage of the midgut epithelium was observed along with lysis.

The toxic effects of neem extract and azadirachtin on the brown planthopper, Nilaparvata lugens (Stål) (BPH) (Homoptera: Delphacidae).

Extracts of neem (Azadirachta indica A. Juss) are used in the developing world for many purposes including management of agricultural insect pests. The effects of different neem extracts (aqueous (NSKEaq), ethanol (NSKEeth) and hexane (NSKEhex)) on mortality, survival and weight of the brown planthopper, Nilaparvata lugens (Stål) (BPH) (Homoptera: Delphacidae) third and fourth nymphal instars were investigated. When fed rice plants treated with neem derivatives in bioassays, the survival of BPH nymphs is affected. Comparisons were made with the pure neem limonoid, azadirachtin (AZA) to ascertain its role as a compound responsible for these effects. AZA was most potent in all experiments and produced almost 100% nymphal mortality at 0.5 ppm and higher concentrations. When higher concentrations were applied, the effects appeared shortly after treatment and mortality was higher. Many insects died after remaining inactive for several days or during prolonged moulting. At lower concentrations, if moulting was achieved, disturbed growth and abnormalities were then likely to occur in the moulting process. Nymphs that were chronically exposed to neem extract showed a reduction in weight (45-60%). The results clearly indicate the simple NSKE (aqueous, ethanolic or both), containing low concentrations of AZA, can be used effectively to inhibit the growth and survival of BPH.