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PubMed1998

Midgut carboxypeptidase from Helicoverpa armigera (Lepidoptera: Noctuidae) larvae: enzyme characterisation, cDNA cloning and expression.

Using synthetic substrates we have characterised carboxypeptidase activity in gut extracts from Helicoverpa armigera larvae. Carboxypeptidase A activity predominates, with only low levels of carboxypeptidase B activity present. Maximum carboxypeptidase A activity occurs over a broad pH range and is inhibited by phenanthroline and potato carboxypeptidase inhibitor. A cDNA clone encoding carboxypeptidase (the first such sequence from a lepidopteran insect) was isolated from a larval gut library. The sequence predicts a secreted polypeptide of Mr 46.6 k with homology to metallocarboxypeptidases from mammalian and invertebrate species. The presence of a serine residue at the active site suggests carboxypeptidase A activity. To further characterise the gene product, the complete cDNA sequence was expressed in insect cells using the baculovirus system. Culture supernatant from these cells contained carboxypeptidase A activity, with no activity against a carboxypeptidase B substrate; the carboxypeptidase B activity in gut extracts must thus be due to a separate enzyme. In agreement with this conclusion, the expressed carboxypeptidase cDNA is a member of a small multigene family. Chronic ingestion of soybean Kunitz trypsin inhibitor by H. armigera larvae results in increased accumulation of carboxypeptidase mRNA in the midgut cells, and an increase in carboxypeptidase A activity detected in gut extract.

Amino Acid Sequence↗
PubMed1999

Characterisation of the helicostatin peptide precursor gene from Helicoverpa armigera (Lepidoptera: Noctuidae).

The gene encoding the helicostatin peptide family was isolated from a Helicoverpa armigera genomic DNA library. The deduced precursor sequence allowed unambiguous identification of all helicostatin peptides and verified the sequences of eight peptides previously isolated. The gene consists of at least three exons and encodes a precursor of 225 amino acids that contains three blocks of tandemly arranged helicostatin peptides including seven copies of the C-terminal sequence -YXFGL followed by a single Gly residue for carboxylamidation. Complete endoproteolytic processing at all possible dibasic cleavage sites would generate the seven helicostatin octapeptides previously purified from larval extracts. If processing was not complete at the third pair of basic amino acids the octadecapeptide (helicostatin IIa) would also be released. Two novel putative helicostatin peptide sequences were identified; YSKFNFGL and ERDMHRFSFGL, both of which had the C-terminal pentapeptide -FXFGL in place of the more usual -YXFGL sequence. Comparison of the helicostatin precursor with that of the cockroaches, locust and flies revealed variation in size, sequence and organisation of the 'allatostatin' precursors across different insect orders. In situ hybridisation histochemistry established that helicostatins are expressed in neurones of the central nervous system and endocrine cells of the midgut, indicating that the helicostatins are true brain-gut peptides. Northern blot analysis identified a single transcript of 1.6 kb in mRNA from whole larvae, isolated central nervous system and gut tissue.

Amino Acid Sequence↗
PubMed2002

Juvenile hormone biosynthesis in the fall armyworm, Spodoptera frugiperda (Lepidoptera, Noctuidae).

The in vitro production of juvenile hormones (JH) was investigated by using corpora allata (CA) of larvae and corpora cardiaca-corpora allata (CC-CA) complexes of adult females of the fall armyworm Spodoptera frugiperda. In female moths, JH release was high compared to that in 5th and 6th instar larvae. Concentrations of 0.11-0.12 mM methionine, 180-200 mM Na(+), 5.8-8.3 mM K(+), 10-50 mM Ca(2+) and a pH range of 5.7-6.3 yielded optimal incorporation of L-[methyl-(3)H] methionine in vitro by CC-CA complexes. The highest hourly incorporation occurred during a 9-h incubation period following a 1.5-h lag-phase. JH release from CC-CA complexes of adult females was shown to be age-dependent with a peak value on day 2 (approx. 4 pmol h(-1) CA(-1)). By a combination of reversed phase (RP)- and normal phase (NP)-high performance liquid chromatography (HPLC), two major labelled products released by the complex were separated. One compound co-migrated with chemically synthesized JH II diol, the second compound with JH III diol. Only traces of JH II and III could be detected in some samples. Gland extracts also contained both the major radiolabelled products. Double labelling experiments using [3H]methionine and [14C]acetate confirmed their de novo synthesis in CC-CA complexes of female moths. The nature of chemically synthesized reference JH III diol was proved by LC-MS (ESI mass spectrometry) and 1H-NMR (nuclear magnetic resonance spectroscopy).

Age Factors↗
PubMed2006

Life history of Spodoptera exigua (Lepidoptera: Noctuidae) on various host plants.

The incubation period of Spodoptera exigua (Hübner) was not influenced by the host plant, whereas larval development time and pupal period were affected. Larval development time was longest on shallot and lady's finger, followed by cabbage and long bean. Larvae did not develop beyond the first instar when fed on chilli. The pupal period was longer on lady's finger than on cabbage, shallot and long bean. Overall, adult longevity was not influenced by the host plant but there was a difference between female and male longevity among the host plants. Survival of S. exigua was affected by the host plant at the larval stage. The number of larval instars varied between 5 and 8 within and between the studied host plants. Long bean was found to be the most suitable host plant and provide the best food quality for S. exigua compared to the other host plants, as it allowed faster development, fewer larval instars and a higher survival rate.

Abelmoschus↗
PubMed2006

The ecology of Helicoverpa spp. (Lepidoptera: Noctuidae) in the Riverina region of south-eastern Australia and the implications for tactical and strategic management.

Decisions on the choice of appropriate tactical and strategic control techniques require an understanding of the seasonal distribution and ecology of the target species. To address this need, data were collected from 1997 to 2000 using crop surveys, field sampling and pheromone trapping to monitor the population trends of Helicoverpa armigera (Hübner) and H. punctigera (Wallengren) in the Riverina region of south-eastern Australia. The data gathered are compared to predictions from the HElicoverpa Armigera and Punctigera Simulation (HEAPS) model, that simulates Helicoverpa population dynamics to assist in identifying the drivers of regional populations and provide a framework to make informed decisions. The results highlight the contrasting seasonal dynamics of H. punctigera and H. armigera within the region. Helicoverpa punctigera populations peak in the spring, driven by large scale spring migration into the region and subsequently decline. Helicoverpa armigera populations, conversely, are characterized by a period of spring recruitment of adults from overwintering pupae within the region, followed by a within-season population increase leading to severe late season pressure. The within-season increase of H. armigera is a result of the succession of crop and non-crop hosts with the main driver being sequentially sown, unsprayed maize. Tactical and strategic management options are discussed in light of these findings.

Animals↗
PubMed2000

Long range forecasts of the numbers of Helicoverpa punctigera and H. armigera (Lepidoptera: Noctuidae) in Australia using the southern oscillation index and the sea surface temperature.

The use of long-term forecasts of pest pressure is central to better pest management. We relate the Southern Oscillation Index (SOI) and the Sea Surface Temperature (SST) to long-term light-trap catches of the two key moth pests of Australian agriculture, Helicoverpa punctigera (Wallengren) and H. armigera (Hübner), at Narrabri, New South Wales over 11 years, and for H. punctigera only at Turretfield, South Australia over 22 years. At Narrabri, the size of the first spring generation of both species was significantly correlated with the SOI in certain months, sometimes up to 15 months before the date of trapping. Differences in the SOI and SST between significant months were used to build composite variables in multiple regressions which gave fitted values of the trap catches to less than 25% of the observed values. The regressions suggested that useful forecasts of both species could be made 6-15 months ahead. The influence of the two weather variables on trap catches of H. punctigera at Turretfield were not as strong as at Narrabri, probably because the SOI was not as strongly related to rainfall in southern Australia as it is in eastern Australia. The best fits were again given by multiple regressions with SOI plus SST variables, to within 40% of the observed values. The reliability of both variables as predictors of moth numbers may be limited by the lack of stability in the SOI-rainfall correlation over the historical record. As no other data set is available to test the regressions, they can only be tested by future use. The use of long-term forecasts in pest management is discussed, and preliminary analyses of other long sets of insect numbers suggest that the Southern Oscillation Index may be a useful predictor of insect numbers in other parts of the world.

Animals↗
PubMed2000

Field evaluation of a slow release pheromone formulation to control the American bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae) in Pakistan.

Trials to control the American bollworm, Helicoverpa armigera (Hübner) by the technique of mating disruption were carried out in the Pakistan Province of Punjab during the 1996 cotton season. A slow release PVC resin formulation, Selibate(R) HA, containing a 97:3 mixture of the major (9Z-hexadecenal) and minor (11Z-hexadecenal) components of the female sex pheromone of H. armigera was applied at a rate of 40 g active ingredient ha-1 during August 1996. The formulation was applied around the terminal portion of the cotton plant by hand using local labour at a rate of c. 250 pieces per hectare. The efficacy of the formulation was compared to conventional insecticide regimes to control H. armigera on four farmer practice fields situated at least 1 km to the north, south, east and west of the pheromone treated area. A high degree of trap catch shutdown (indicating mating suppression) was observed throughout the pheromone treated area during the whole of the season compared to non-pheromone treated farmer practice fields. Night observations confirmed that mating disruption occurred in the pheromone treated area as a smaller percentage of mated females were collected from this area compared to farmer practice fields. A majority of mated females collected from the pheromone treated area mated only once, whereas females in farmer practice fields had undergone multiple matings. A greater percentage of tethered female H. armigera moths retrieved from farmer practice fields had successfully mated compared to tethered females retrieved from the pheromone treated area. Release rate data of H. armigera pheromone from the formulation show that c. 70% was released during the two month trial period. However, the highly dispersive pre-oviposition flight behaviour of females meant that the area treated was not sufficient to eliminate the problem of gravid females migrating in from surrounding areas, and ovipositing therein. The implications of using the technique of mating disruption to control large strong flying insects like H. armigera are discussed.

Aldehydes↗
PubMed2000

The biology of Meteorus gyrator (Hymenoptera: Braconidae), a solitary endoparasitoid of the tomato moth, Lacanobia oleracea (Lepidoptera: Noctuidae).

There is a need to identify potential biological control agents for use against lepidopterous pests in greenhouses. The solitary endoparasitoid Meteorus gyrator (Thunberg) attacks a range of macrolepidopterous larvae, including those of some important horticultural pest species. Laboratory trials designed to investigate the biology of M. gyrator on larvae of the tomato moth, Lacanobia oleracea Linnaeus, reveal that this parasitoid is capable of parasitizing all larval stages of its host, third instars being parasitized most frequently. Each female parasitoid lives for up to 40 days (at 25 degrees C), ovipositing into an average of 78 hosts. Preadult development is rapid ( approximately 2 weeks), and the sex ratio of offspring is 1:1. Parasitism by M. gyrator suppresses the growth of both early and late host instars, and there is a concomitant reduction in the amount of food consumed (overall feeding reduction over a 12 day period is 68%). Our results indicate that inoculative releases of M. gyrator could provide effective biological control of L. oleracea and other noctuid pests of greenhouses.

Animals↗
PubMed2006

Morphological and molecular characterization of a new microsporidian (Protozoa: Microsporidia) isolated from Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae).

A microsporidium was isolated from larvae of Spodoptera litura (Fabricius) collected from Tamil Nadu, India. This microsporidian species is monomorphic, disporous and develops in direct contact with the cytoplasm of the host cell. The nuclear configuration of merogonic and sporogonic stages was diplokaryotic. The merogonic proliferative stage was unusual that normal development with 1, 2 and 4 binucleated forms were common, while large multinucleate meronts containing 8 and 12 small compact horseshoe-like diplokaryotic nuclei were also observed. The fresh spores were typically ovocylindrical in shape, with a mean size of 3.91 x 1.91 microm and the polar filament length was approximately 90 microm. Infection was systemic with mature spores produced in the midgut, nervous tissue, muscles, labial glands, gonads, tracheae, epidermis, Malpighian tubules and, most extensively, fat body tissues. The new isolate was highly pathogenic to S. litura larvae. Host specificity tests performed on 37 non-target hosts of 5 different insect orders revealed that the new isolate is pathogenic only to lepidopteran insects. We sequenced the 16S small subunit rRNA (SSU rRNA) gene of the isolate and compared it with 72 non-redundant microsporidian sequences from the GenBank. Based on the light microscopic studies and phylogenetic analyses, the new isolate is assigned to the genus Nosema. Significant differences in the SSU rRNA sequence were identified when compared with the type species Nosema bombycis and other closely related species viz., Nosema spodopterae. Structural differences were also observed in the 16S SSU rRNA between the new isolate and the two above-mentioned microsporidian pathogens. We conclude that the microsporidian isolate reported here is distinctly different from the other known species and is likely to be a new species.

Animals↗
PubMed2001

Acute, sublethal, antifeedant, and synergistic effects of monoterpenoid essential oil compounds on the tobacco cutworm, Spodoptera litura (Lep., Noctuidae).

Monoterpenoids (terpenes and biogenically related phenols) commonly found in plant essential oils were tested for acute toxicity via topical application to tobacco cutworms (Spodoptera litura Fab.). The most toxic among 10 such compounds was thymol (LD(50) = 25.4 microg/larva) from garden thyme, Thymus vulgaris. The compounds were then tested for sublethal effects, specifically inhibition of larval growth after topical application of low doses. Among 6 compounds tested, an LD(10) dose reduced growth by 20% on average 3 days after administration. Feeding deterrence was determined using a cabbage leaf disk choice test. The most deterrent compound was thymol, with a DC(50) of 85.6 microg/cm(2) leaf disk area. Because minor constituents in complex essential oils have been suggested to act as synergists, binary mixtures of the compounds were tested for synergy vis à vis acute toxicity and feeding deterrence. trans-Anethole acted synergistically with thymol, citronellal, and alpha-terpineol, in terms of both acute toxicity and feeding deterrence. On the basis of these findings, several complex mixtures were developed and tested as leads for effective control agents. Candidate mixtures demonstrated good synergistic effects. The observed LD(50) of mixture 3 was 40.6 microg/larvae compared to an expected value of 74.6 microg/larvae. The result of this research is a proprietary product suitable for commercial production.

Animals↗
PubMed2004

Metabolism of thymol and trans-anethole in larvae of Spodoptera litura and Trichoplusia ni (Lepidoptera: Noctuidae).

Metabolism of the monoterpenoid thymol and the phenylpropanoid trans-anethole, both constituents of essential oils, was investigated following topical and oral administration of the compounds to the tobacco cutworm (Spodoptera litura) and the cabbage looper (Trichoplusia ni). In both species and irrespective of route, administration of thymol resulted in the excretion of its 3-O-beta-glucoside, whereas trans-anethole was hydroxylated on the side chain methyl group. Both metabolites were isolated and their structures elucidated by interpretation of their mass and NMR spectra. Previous experiments indicated that trans-anethole synergized the toxicity of thymol in S. litura, but analyses of feces indicated that metabolism of thymol was not significantly suppressed when the two compounds were orally coadministered to T. ni larvae.

Allylbenzene Derivatives↗
PubMed2006

Putative role of pith cell wall phenylpropanoids in Sesamia nonagrioides (Lepidoptera: Noctuidae) resistance.

The stem borer Sesamia nonagrioides (Lefèbvre) is the most important insect pest that attacks maize, Zea mays L., in northwestern Spain. Host plant resistance to this borer was investigated in relation to the cell wall phenylpropanoids content in the pith. Eight inbred lines that differ in resistance were analyzed. Three major simple phenolic acids, p-coumaric, trans-ferulic, and cis-ferulic acids, and three isomers of diferulic acid, 8-5', 8-O-4', and 8-5'b (benzofuran form), were identified. The amount of all these compounds was correlated with the resistance level in the genotypes, with the resistant inbreds having the highest concentrations. The role of these compounds in cell wall fortification and lignification is well-documented, suggesting their possible intervention in S. nonagrioides resistance. Future studies that focus on these compounds could be useful to enhance S. nonagroides resistance.

Animals↗
PubMed2006

Preparation of monoclonal antibody against celangulin V and immunolocalization of receptor in the oriental armyworm, Mythimna separata walker (Lepidoptera: Noctuidae).

The botanical insecticide celangulin V (CA-V) is an insect digestive poison acting on midgut tissue of the target insect larvae. With the aim of localizing the receptor enacted by CA-V, monoclonal antibodies (MAbs) specific to the compound were developed. A hapten was synthesized by introducing a succinoyl into the CA-V structure and conjugated with three carrier proteins. From mice immunized with one conjugate, three MAbs were obtained with a potential capacity of detecting protein-bound residue forms of CA-V in the biological tissues. The oriental armyworm larvae ingested CA-V were examined by the technique of immuno-electron-microscopy (IEM) using the anti-CA-V MAb as the primary antibody and goat anti-mouse/IgG labeled with colloidal gold as the secondary antibody. Electron micrographs of the armyworm midgut tissues showed that the CA-V was associated with the midgut epithelia of the insects. These results demonstrated the existence of a receptor enacted by CA-V on the midgut cells of the oriental armyworm larvae.

Animals↗
PubMed2006

Diferulate content of maize sheaths is associated with resistance to the Mediterranean corn borer Sesamia nonagrioides (Lepidoptera: Noctuidae).

The leaf sheaths of selected inbred lines of maize (Zea mays L.) with variable levels of stem resistance to the Mediterranean corn borer Sesamia nonagrioides (Lefèvbre) were evaluated for antibiotic effect on insect development. Phytochemical analyses of leaf sheaths were conducted for cell wall phenylpropanoid content to gain a better understanding of maize-resistance mechanisms. Laboratory bioassays established that sheath tissues from different genotypes significantly affected the growth of neonate larvae. Three hydroxycinnamates, p-coumaric, trans-ferulic, and cis-ferulic acids, and three isomers of diferulic acid, 8-5', 8-O-4', and 8-5' b (benzofuran form), were identified. Significant negative correlations were found between larvae weight and diferulic acid content for six genotypes. These results are in agreement with previous studies concerning the role of cell wall structural components in stem borer resistance.

Animals↗
PubMed2001

Transgenic GNA expressing potato plants augment the beneficial biocontrol of Lacanobia oleracea (Lepidoptera; Noctuidae) by the parasitoid Eulophus pennicornis (Hymenoptera; Eulophidae).

The effect of expressing the gene encoding snowdrop lectin (Galanthus nivalis agglutinin, GNA) in transgenic potato plants, on parasitism of the phytophagous insect pest Lacanobia oleracea by the gregarious ectoparasitoid Eulophus pennicornis, was investigated in glasshouse trials. Expression of GNA (approx. 1.0% total soluble protein) by transgenic plants significantly reduced the level of pest damage, thus confirming previous studies. Furthermore, the presence of the parasitoid significantly reduced the levels of damage incurred either by the transgenic or control plants when compared to those plants grown in the absence of the parasitoid. For the GNA expressing plants the presence of the parasitoid resulted in further reductions (ca. 21%) in the level of damage caused by the pest species. The ability of the wasp to parasitise and subsequently develop on the pest larvae was not altered by the presence of GNA in the diet of the host. E. pennicornis progeny that developed on L. oleracea reared on GNA expressing plants showed no significant alteration in fecundity when compared with wasps that had developed on hosts fed on control potato plants, although mean size and longevity of female parasitoids was significantly reduced. The number of F2 progeny produced by parasitoids derived from hosts fed on GNA expressing plants was not significantly different to those produced by parasitoids from hosts fed control plants. Results from the present study demonstrate that the use of transgenic plants expressing insecticidal proteins can be compatible with the deployment of beneficial insects and that the two factors may interact in a positive manner.

Animals↗
PubMed2002

Genetic differentiation between alternate-year cohorts of Xestia tecta (Lepidoptera, Noctuidae) in Finnish Lapland.

Several species in the noctuid genus Xestia exhibit periodic dynamics, with two coexisting cohorts flying in alternate years. The population dynamics and two-year life cycle of Xestia moths suggest that the two cohorts are more or less isolated in time. Typically one cohort is abundant and the other one is rare. Knowledge of the extent of isolation between the two cohorts is important to fully understand the population dynamics and the evolution of alternate-year flight in these species. We applied allozyme electrophoresis and mitochondrial genome sequencing to infer the extent of genetic differentiation among different cohorts of Xestia tecta (Hübner) within the same geographical area as well as between cohorts with opposite-phase flight pattern in different geographical regions. We found no evidence for substantial genetic differentiation and isolation between the even- and odd-year cohorts in eastern Lapland, nor between the cohorts in eastern and western Lapland. The most informative markers were the most polymorphic allozyme loci (Pgm and Mpi) and the AT-rich region in the mtDNA. However, owing to the generally low levels of genetic variation it was not possible to establish conclusively the degree of genetic isolation between the different cohorts. We discuss the implications of our results in relation to two different hypotheses which could account for this pattern: ongoing gene flow between different cohorts and recent common ancestry.

Animals↗