Tobacco Cutworm Spodoptera Litura Research Articles

Toxicity of Alangium salvifolium Wang chemical constituents against the tobacco cutworm Spodoptera litura Fab

Widespread use of synthetic pesticides has resulted in the development of insecticide-resistant populations of pests and harmful effects on human health and the environment. There is a need to identify alternative pest management strategies to reduce our reliance on conventional chemical pesticides. In recent years the use of botanical pesticides for protecting crops from insect pests has assumed greater importance. Methanol extract of Alangium salvifolium (L.f.) Wang has potential insecticidal activity against Spodoptera litura Fab. The active fractions were identified through chromatographic techniques as F-IV (Rf value=0.45) and F-VI (Rf value=0.63) and were subjected to GC–MS (GCMATE II). Fifty, 100 and 200ppm of active fractions were applied to fourth instar larvae and the mortality increased with higher concentrations. Relative consumption rate, relative growth rate, efficiency of conversion of ingested food and efficiency of conversion of digested food values all decreased in treated larvae, but approximate digestibility rate increased after treatment. The hydrolytic enzymes, such as acid phosphatase, alkaline phosphatase and the glycolytic enzyme lactate dehydrogenase were inhibited in treated larvae compared with controls. The histopathology study revealed that the epithelial columnar cells were enlarged, completely atrophied; intercellular spaces were swollen, and also noted a cytoplasmic ooze of cell material that mixed with food column. The present study clearly showed the active fractions from A. salvifolium as potential botanicals to control the larvae of S. litura. This is the first report for nutritional indices, enzymatic activities and histological effects of A. salvifolium chemical constituents against S. litura. Thus probably, this will be used as an alternative for synthetic pesticides against the polyphagous pest like S. litura.

Bacillus subtilis chitinase identified by matrix-assisted laser desorption/ionization time-of flight/time of flight mass spectrometry has insecticidal activity against Spodoptera litura Fab.

An extracellular chitinase was identified and purified (CS1 and CS2) from Bacillus subtilis. The 16S rRNA sequencing was submitted in GenBank (accession numbers KC336487 and KC412256). The purified crude enzymes were identified through matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF MS) analysis. The peptide sequences were matched with chitinase sequences. The peak m/z with 1297. 592 and 3094.570 mascot search resulted sequence was blasted with NCBI protein sequences and confirmed that it is a chitinase enzyme. The effects of chitinase on gut enzymes lactate dehydrogenase, acid phosphatase, alkaline phosphatase and adenosine triphosphatase of the tobacco cutworm Spodoptera litura larvae were investigated. At all concentrations tested, chitinase decreased the activities of these gut enzymes relative to the control. When chitinase treated leaves were fed to larvae in bioassays, gut tissue and gut enzymes were affected. The histological study clearly shows the chitinase treated larval gut, peritrophic membrane and epithelial cells were affected significantly. Chitinase isolated from B. subtilis has effectively reduced the gut enzyme activity and growth of S. litura. The chitin based bioformulation may serve as an effective biocide against the polyphagous pest like S. litura.

Development and emergence patterns of the tobacco cutworm Spodoptera litura (Lepidoptera: Noctuidae)

Study of lifecycle patterns and rhythms is important to understand the ecology and evolution of insects. The tobacco cutworm Spodoptera litura (Lepidoptera: Noctuidae), is a serious polyphagous pest in Asia, Oceania and the Indian subcontinent. The laboratory investigations of development patterns and circadian rhythms described in this paper have shown that the development duration from egg to pupae is 21.5 ± 0.7 d in which the pupation peak took place in the 21st day after eggs being laid. The development duration from egg to adult is 33.0 ± 0.8 d and 35.0 ± 0.7 d for female and male moths, respectively. Adult emergence showed a circadian rhythm in both sexes where adults start to emerge in the afternoon and increased quickly and peaked at dusk and then declined gradually in a few hours into the night. The present study suggests that S. litura is a protogynous species. Protogyny may be a mechanism that has evolved to reduce inbreeding because early emerged females are less likely to mate with their brothers. In S. litura, eggs are laid in clusters with a cluster contain 50-300 eggs, from which inbreeding risks are increased due to offspring live together with high population density. Therefore, females emerge earlier than males should be extremely important in S. litura, and inbreeding avoidance should be the main forth behind the evolution of protogyny in this insect.

Molecular characterization and functional analysis of a putative sex-peptide receptor in the tobacco cutwormSpodoptera litura(Fabricius, 1775) (Lepidoptera: Noctuidae)

The sex-peptide receptor (SPR) acts in Drosophila females to detect male sex-peptide (SP) and trigger changes in female behaviour. Further study on SPR and its ligand family from different taxa will not only provide insight into ligand–receptor coevolution but also facilitate finding new approaches for pest control. Our previous studies on the tobacco cutworm Spodoptera litura (Fabricius, 1775) showed that mating usually results in marked changes in female behaviour and determined that factors from male accessory gland (MAG) secretions play a key role in such switches in females after mating. In the present study, we report the cloning of a transcript encoding a G-protein-coupled receptor from S. litura. This 3 kb transcript contains an ORF encoding a protein of 421 amino acids that shared significant amino acid identity to the SPR identified in Drosophila. Real-time PCR showed that the expression levels of the receptor in adults correlate well with the process of sexual maturation and mating rates; mating resulted in distinct sexual dimorphic differences in gene expression. Our results suggest that this gene is involved in mediating reproductive behaviour in adult moths. To test the hypothesis, we further studied the possible function of this receptor (SplSPR) on mediating female post-mating behaviour by using RNA interference (RNAi) and treatment with MAG secretions. RNAi reduced the expression levels of SplSPR by 65–88% and significantly prevented the effect of MAG secretions. Injection of MAG secretions causes normal virgin females to behave as though they had mated (they are sexually unreceptive and start to lay eggs), whereas SPR RNAi females fail to respond to MAG factors and continue to show virgin behaviours (lay very few eggs and copulate readily). These results support the hypothesis that the SplSPR functions in mediating female post-mating behaviour and the existence of an SP-like ligand in MAG secretions in S. litura.

Physiological effect of chitinase purified from Bacillus subtilis against the tobacco cutworm Spodoptera litura Fab.

An extracellular chitinase was purified from Bacillus subtilis. The lethal concentration (LC50) was determined by using chitinase in first, second, and third instars of Spodoptera litura Fab. Chitinase showed the highest insecticidal activity at 6μM concentration within 48h. The nutritional indices were also significantly affected by the 6μM concentration (P<0.05). Food consumption, efficiency of conversion of ingested and digested food, relative growth rate, and consumption values declined significantly while approximate digestibility was increased. Our study indicates that treatment of host plant leaves with the chitinase can regulate (reduce) larval growth and weight, and enhance the mortality. This may serve as an effective biocide and alternative to Bt toxin.

Impact of antennectomy, eye blinding and tibial comb coating on the predatory behaviour of Rhynocoris kumarii Ambrose and Livingstone (Het., Reduviidae) on Spodoptera litura Fabr. (Lep., Noctuidae)

The predaceous reduviid Rhynocoris kumarii uses its antennae, eyes and tibial comb to predate tobacco cutworm Spodoptera litura (Fabr). A delayed arousal response was observed in the antennectomized, eye blinded and tibial comb‐coated predators. The predators whose entire antennae had been removed showed significant delayed approach but the approach response was not affected significantly in the blinded and tibial comb‐coated reduviid predators. Capturing response was significantly affected in pedicel and entire antennae‐removed predators, and blinded and tibial comb‐coated predators. Antennectomy, eye blinding and tibial comb coating did not cause any impact in the act of paralysing the prey. Progressive reduction in sucking duration and the number of sucking sites were observed as a function of sequential segment‐wise removal of antennae. A reduction in the sucking duration and number of sucking sites were also observed in blinded and tibial comb coated predators.

Electrophoretic Pattern of Larval Esterases in Field and Laboratory-selected Strains of the Tobacco Cutworm, Spodoptera litura (Fabricius)

This research was performed to find out and characterize the specific esterase isozymes related to OP and pyrethroid resistance in the tobacco cutworm Spodoptera litura (Fabricius). Two laboratory strains (DSR 5 and CSR 4) of S. litura, selected with deltamethrin and chlorpyrifos-methyl, had higher larval esterase activities than Hamancollected (HC) strain. Ten esterase isozymes were separated in the wild HC strain on 6.5% nondenaturing polyacrylamide gel electrophoresis (pH 8.3), but only 5 of them were detected in the two strains selected with insecticides. The isozymes were designated from E1 to E10 according to their mobility to cathode. E4 was stained more strongly in both laboratory-selected strains than in HC strain. The frequency of E2 in DSR 5 strain was higher than in HC strain. E2 and E4 were proved to be arylesterase and carboxyesterase, respectively, according to enzyme inhibition tests. Thus decreased number and increased intensity of esterase bands in DSR 5 and CSR 4 strain may be associated with insecticide resistance, resulting from selections successively with insecticides for several generations.

Cyclohexadienones-insect growth inhibitors from the foliar surface and tissue extracts ofSenecio cannabifolius

Dewaxed leaf surface extracts of 12 plants from Hokkaido, prepared by dipping fresh leaves in chloroform for 3 min, were used in a choice leaf-disk bioassay against larvae of the tobacco cutwormSpodoptera litura. Activity was found only in the extract ofSenecio cannabifolius, a very successful weed in Hokkaido. Individual fractions of the extract, however, were not active. Incorporation of the individual fractions of the surface extracts as well as fractions of the methanolic extracts of the leaf residue into an artificial diet fed to neonateS. litura led to the isolation of ethyl (1-hydroxy-4-oxocyclohexa-2,5-dien-1-yl) acetate, the major surface compound, as the active principle. This compound was also present in the methanolic extract of the leaf residue together with methyl (1-hydroxy-4-oxocyclohexa-2,5-dien-1-yl) acetate, which had the same growth inhibitory effect on the larvae. The presence of these compounds in the foliar surface and tissue suggests a defensive role against herbivores.