Egyptian Armyworm Research Articles

Cry3Aa Toxin Is Not Suitable to Control Lepidopteran Pest Spodoptera littoralis (Boisd.).

The toxicity of the Bacillus thuringiensis (Bt) toxin Cry3Aa—originally used against the main potato pest, the Colorado potato beetle, Leptinotarsa decemlineata—was verified on this species and then evaluated against the Egyptian armyworm, Spodoptera littoralis, which is a pest of several economically important plants. Larvae of S. littoralis were fed a semi-artificial diet supplemented either with a recombinant or with a natural Bt toxin Cry3Aa and with the genetically engineered (GE) potato of variety Superior NewLeaf (SNL) expressing Cry3Aa. Cry3Aa concentration in the diet and the content in the leaves were verified via ELISA (enzyme-linked immunosorbent assay) and HPLC (high-performance liquid chromatography) during and at the end of the experiments. The biological effectiveness of the coleopteran-specific Cry3Aa with previous reports of activity against S. littoralis was tested on five different populations of S. littoralis larvae by monitoring 13 parameters involving development from penultimate instar, weight, the efficiency of food conversion to biomass, ability to reproduce, and mortality. Although some occasional differences occurred between the Cry3Aa treatments and control, any key deleterious effects on S. littoralis in this study were not confirmed. We concluded that the Cry3Aa toxin appears to be non-toxic to S. littoralis, and its practical application against this pest is unsuitable.

Penta‐deuterated acid precursors in the pheromone biosynthesis of the Egyptian armyworm, Spodoptera littoralis

AbstractSynthesis of penta‐deuterated intermediate precursors d5(E)‐11‐14:Acid (7), d5(Z)‐11‐14:Acid (10) and d514:Acid (12) of the pheromone of the Egyptian armyworm Spodoptera littoralis has been accomplished by a very convenient route starting from the commercially available 9‐dodecyn‐1‐ol. The processes occur with a high to excellent chemical and stereochemical yields and the compounds have been successfully used in the confirmation of the pheromone composition and biosynthesis of our strain. Copyright © 2009 John Wiley & Sons, Ltd.

Biosynthetic pathways of the pheromone of the Egyptian armyworm Spodoptera littoralis

Abstract Most insect pheromones comprise multicomponent blends of geometric or optical isomers, and one major question is how insects produce species‐specific ratios of components for successful reproductive isolation. Key enzymes suggested to be involved in pheromone biosynthesis are acetyl‐coenzyme A carboxylase and fatty acyl synthetase, chain‐shortening enzymes, desaturases, elongases, reductases, oxidases, and alcohol acetyl transferases. The female pheromone composition of the Egyptian armyworm Spodoptera littoralis (Boisd.) is highly dependent on the origin of the strain. In this review, we present a summary of the different reported pheromone compositions of the moth, including from our recent studies on this subject, as well as the biosynthetic routes to the different components and the molecular approaches involved. In addition, the key role played in the proposed biosynthetic pathways by a number of important biosynthetic enzymes, such as chain shortening enzymes, desaturases and alcohol acetyl transferases, is outlined, as well as the latest developments on the inhibition of these enzymes.

Molecular characterization of an inhibitor of apoptosis in the Egyptian armyworm, Spodoptera littoralis, and midgut cell death during metamorphosis

The cDNA corresponding to an inhibitor of apoptosis (IAP) from the Egyptian armyworm, Spodoptera littoralis, was cloned by RT-PCR. Sequence analysis showed that the IAP of S. littoralis (SlIAP) contains two baculoviral IAP repeat (BIR) motifs, followed by a RING finger, an organization which is very similar to that of other lepidopteran IAPs. SlIAP mRNA was detected in ovary, testis, salivary gland, fat body, epidermis, brain and midgut of S. littoralis. During the last larval instar, prepupal and pupal stages, brain mRNA levels remained approximately constant, whereas those of midgut showed a large peak centred in the prepupal stage. Midgut morphology changed during metamorphosis from a semi-transparent, cylindrical structure in last instar larvae to a brownish globular mass in pupae. TUNEL assays, LysoTracker staining and caspase-3 immunohistochemistry, indicated that programmed cell death in midgut starts actively at the onset of pupation process, coinciding with the dramatic decrease of SlIAP mRNA levels observed at the same time.

Antennal esterase cDNAs from two pest moths, Spodoptera littoralis and Sesamia nonagrioides, potentially involved in odourant degradation

Rapid degradation of odours after interaction with olfactory receptors is a critical step of the signal reception process. However, the implied mechanisms are still largely unknown in vertebrates as well as in insects. Involvement of odourant-degrading enzymes in odourant degradation within the antennae has been shown in some insect species and, in particular, esterases could play a key role in degradation of sex pheromones from Lepidoptera. Using a PCR-based strategy, we isolated cDNAs encoding two new esterases from two moths which used acetates as pheromone compounds: the Egyptian armyworm Spodoptera littoralis and the Mediterranean corn borer Sesamia nonagrioides. In antennae, both transcripts were clearly restricted to olfactory sensilla, suggesting their involvement in the degradation of odourant acetate components.

Antioxidant enzymes in Spodoptera littoralis (Boisduval): Are they enhanced to protect gut tissues during oxidative stress?

The Egyptian armyworm Spodoptera littoralis is a polyphagous insect attacking a number of plant species including those belonging to the Solanaceae and Cruciferaceae families. Its digestive physiology must therefore adapt to the food plant to ensure maximum extraction of nutrients with minimum trade-off in terms of growth retardation by pro-oxidant allelochemicals. To investigate this, the caterpillars of S. littoralis were fed on a semi-artificial diet ( Manduca Premix– Heliothis Premix) and for 24 h on potato plants ( Solanum tuberosum), respectively, at the mature 6th instar, and the levels of oxidative radicals and antioxidant enzymes in their guts were compared. The gut pH, standard redox potential (E h) and electron availability (pe) revealed that oxidizing conditions prevail which promote oxidation of pro-oxidant allelochemicals in foliage. Oxidative stress in the foregut and midgut tissue and the gut contents was assessed from the generation of superoxide radical, total peroxide content and protein carbonyl content. Antioxidant defense was measured by the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APOX) and glutathione S-transferase peroxidase (GSTpx). A significant ( p<0.001) increase in the superoxide radical production (in foregut tissue, foregut and midgut contents), concomitant with an increase in total peroxide (in foregut contents) and protein carbonyl levels (in foregut and midgut tissue) were noted in larvae fed on the plants in contrast to those fed the semi-artificial diet. Similarly, a significant up-regulation of antioxidant enzymes SOD (in midgut tissues), CAT (in foregut, midgut tissue and contents), APOX (in foregut contents, midgut tissue and contents) and GSTpx (in foregut tissues) was recorded on the plant diet in comparison to the semi-artificial diet. The pro-oxidant allelochemicals in the plant diet are thus eliminated by the insect at the expense of up-regulation of antioxidative enzymes in response to increased oxidative stress from oxidizable allelochemicals. The results are consistent with the hypothesis that increased concentrations of antioxidants form an important component of the defense of herbivorous insects against both exogenous and endogenous oxidative radicals.

Beetle‐specific Bacillus thuringiensis Cry3Aa toxin reduces larval growth and curbs reproduction in Spodoptera littoralis (Boisd.)

Application of Bacillus thuringiensis tenebrionis (Bt) and expression of the Bt protein Cry3Aa in genetically modified crops are used for targeted control of the Colorado potato beetle Leptinotarsa decemlineata (Say). The Cry3A proteins are selectively toxic for the beetles but the present study describes effects of Cry3Aa on the Egyptian armyworm, Spodoptera littoralis (Boisduval). Cry3Aa expressed in potatoes or added to an agar-base wheat-germ diet reduced the growth of S. littoralis caterpillars and the fertility of adults. The effect of 1.4 mg kg(-1) Cry3Aa in potato leaves was comparable with that of 3.3 mg kg(-1) in the diet. This difference in activity was correlated with better digestibility and higher conversion efficiency of the diet that also supported higher reproduction rate: S. littoralis grown on the potatoes reached a similar size to those on the diet but laid only 702 instead of 1077 eggs per female. Cry3Aa consumption reduced body growth as a consequence of lower food intake without significantly affecting food digestibility and the conversion efficiency of nutrients. The 11% and 5% body weight reductions caused by 1.4 mg kg(-1) Cry3Aa in potatoes and 3.3 mg kg(-1) in the diet, respectively, were associated with 74% and 65% reduction in the number of progeny; S littoralis grown on a diet with 9.1 mg kg(-1) Cry3Aa were 10% smaller and produced no viable progeny. These data suggest that the curtailment of reproduction was not caused by a general shortage of nutrient reserves but by a more direct Cry3Aa effect on the reproduction process.

Synthesis of fluorinated analogs of myristic acid as potential inhibitors of egyptian armyworm (Spodoptera littorialis) Δ11 desaturasedesaturase

To study the activity of the different desaturases present in the pheromone biosynthetic pathway of the Egyptian armyworm, Spodoptera littoralis, we prepared a series of mono- and gem-difluorinated analogs of myristic acid with halogen substitution at the C8-C11 positions of the aliphatic chain via specifically positioned dithiane precursors. Thus, transformation of dithianes by treatment with N-bromosuccinimide in the presence of H2O followed by reduction with LiAlH4 afforded the appropriate alcohols, which reacted with diethylaminosulfur trifluoride to give rise to the corresponding monofluoroderivative intermediates. Alternatively, the introduction of the gem-difluoro functionality was carried out by reaction of the appropriate dithiane intermediate with 1,3-dibromo-5,5-dimethylhydantoin in the presence of HF/pyridine. The activity of these fluorinated FA as substrates and inhibitors of the desaturases involved in the biosynthesis of the sex pheromonal blend of S. littoralis has been studied. In this case, 11-fluorotetradecanoic acid elicited a moderate inhibitory activity of delta11 desaturase.

New fluorinated derivatives as esterase inhibitors. Synthesis, hydration and crossed specificity studies

A variety of new fluorinated chemicals have been prepared for the first time and tested as inhibitors of esterases, one of the main enzymes involved in pheromone catabolism, in two economically important pests, the Egyptian armyworm Spodoptera littoralis ( SL) and the Mediterranean corn borer Sesamia nonagrioides ( SN). Using the respective major component of the pheromone as substrate, the K m and V max of the antennal esterase of both insects resulted to be 5.66×10 −4 M and 8.47×10 −6 Mmin −1 for SL and 1.61×10 −7 M and 1.25×10 −7 Mmin −1 for SN, pointing out that SN esterase has a higher affinity for its corresponding substrate than SL. In general, the trifluoromethyl ketones (TFMKs) exhibited higher inhibitory potency than the corresponding difluoromethyl ketones (DFMKs) or difluoroaldehydes (DFAs). The compounds appeared to hydrate differently in aqueous solution, the extent of hydration following the order: α,α-DFMKs<α,α-difluoro-β-thioalkylmethyl ketones<TFMKs<β-thiotrifluoromethyl ketones<α,α-DFAs. No clear correlation has been found between the K hyd and the inhibitory potency and no specificity has been found when the chemicals were assayed on extracts of both insects.

Analytical studies of Spodopteralittoralis sex pheromone components by electroantennography and coupled gas chromatography–electroantennographic detection

In this paper we present analytical studies of the sex pheromone components of the Egyptian armyworm Spodoptera littoralis (Lepidoptera, Noctuidae) by electroantennography (EAG) and coupled gas chromatography-electroantennographic detection (GC-EAD). EAG responses in three different preparations, using an insect's head, an excised antenna and a live insect, have been recorded. EAG depolarizations of live insects were significantly higher than those elicited by the insect's head or the excised antenna. The responses were dose-dependent. Live insects also allowed regular pheromone stimulations for 40 min with only 38% decrease of the EAG initial depolarization. The synthetic pheromone blend elicited the highest EAG activity (2.0±0.3 mV), followed by the major compound ( Z, E)-9,11-tetradecadienyl acetate ( I) (1.54±0.1mV), and the minor components ( Z)-9-tetradecenyl acetate ( II), ( E)-11-tetradecenyl acetate ( III), tetradecyl acetate ( IV) and ( Z)-11-tetradecenyl acetate ( V) (1.21-1.32 mV range). ( Z, E)-9,12-tetradecadienyl acetate ( VI), although not present in the pheromone blend of our strain, also showed an EAG activity (1.32±0.09 mV) similar to that of the monoenic components. GC-EAD responses confirmed the composition of the sex pheromone blend, the major response being elicited by the main component I followed by the other minor compounds II-V. The new dienic compound found in the female pheromone gland, ( E, E)-10,12-tetradecadienyl acetate ( VII), was not electrophysiologically active. Regarding sensitivity, the minimum amount detectable to elicit an antennal response in our GC-EAD system was 15 pg of the major component. In our system, which was built with cheap and easily available materials, no cooling of the effluent at the outlet of the chromatographic column is required.

Pheromone-triggered orientation flight of male moths can be disrupted by trifluoromethyl ketones.

In a wind tunnel trifluoromethyl ketones (TFMKs) have been found to disrupt the orientation flight of male moths to pheromone sources (virgin females or synthetic pheromone). This is demonstrated by comparison of the flight parameters of the Egyptian armyworm Spodoptera littoralis and the Mediterranean corn borer Sesamia nonagrioides, which had been topically treated with TFMKs, with those calculated for untreated insects. Inhibition occurred in all types of behavior and that of the source contact has been quantified and found to be dose-dependent. The same effect has also been noticed in Mediterranean corn borer males flying to an attraction source consisting of mixtures of (Z)-11-hexadecenyl trifluoromethyl ketone (8), a closely related analogue of the major component of the pheromone, and the natural pheromone blend. The most active TFMKs are those closest in structure to the natural pheromone, along with those chemicals which easily hydrate in solution, such as the beta-thiosubstituted derivatives. Along with the previously reported reduction of catches in the field, our results suggest the possible application of these chemicals in future new pest control strategies.

Synthesis of tritiated sex pheromones of the processionary moth Thaumetopoea pityocampa and the Egyptian armyworm Spodoptera littoralis

Synthesis of tritiated sex pheromones of the processionary moth Thaumetopoea pityocampa and the Egyptian armyworm Spodoptera littoralis

Synthesis of tritiated sex pheromones of the processionary moth Thaumetopoea pityocampa and the Egyptian armyworm Spodoptera littoralis

Synthesis of tritiated sex pheromones of the processionary moth Thaumetopoea pityocampa and the Epyptian armyworm Spodoptera littoralis has been accomplished by a simple route involving tritiated sodium borohydride reduction of the corresponding aldehyde followed by acetylation of the resulting radiolabelled alcohol. The process occurs with high chemical and radiochemical yields and the compounds have been used in pheromone catabolism studies.

Fate of the chromene encecalin in the interaction ofEncelia farinosa and its specialized herbivoreTrirhabda geminata

Leaf beetles of the speciesTrirhabda geminata are specialized herbivores that are able to feed on the chemically well-protected foliage of the desert sunflowerEncelia farinosa, which contains the insecticidal chromene derivative encecalin. Chemical analysis of the beetles and their fecal excretions indicated that encecalin is present only in the alimentary canal and is not absorbed across the gut membrane, as previously shown for other herbivorous insects (e.g., the Egyptian armyworm,Spodoptera littoralis) that are susceptible to this chromene derivative. Further differences betweenT. geminata and nonadapted insects were observed with regard to the metabolism of encecalin. Whereas the encecalin-resistent leaf beetles metabolize encecalin mainly to encecalol by reduction of the acetyl group, susceptible insects, such as larvae ofS. littoralis, metabolize encecalin mainly by exoxidation of the 3,4 double bond, which creates a powerful alkylating agent and is responsible for the toxicity of encecalin. Reductive rather than oxidative metabolism of encecalin therefore seems important for the resistance ofT. geminata against the chemical defense of their host plantE. farinosa.

Difluoropalmitic acids as potential inhibitors of the biosynthesis of the sex pheromone of the Egyptian armyworm Spodoptera littoralis—IV

2,2-, 3,3- and 4,4-Difluoropalmitic acids ( 1–3) have been synthesized and fully characterized. Acids 2 and 3 were prepared through fluorination of the corresponding dithioacetal-protected ketoesters followed by enzymatic saponification. The acids 1–3 were evaluated in vivo as inhibitors of the β-oxidation step of the biosynthesis of ( Z, E)-9,11-tetradecadienyl acetate, the major component of the sex pheromone of the Egyptian armyworm Spodoptera littoralis. Only, the 2,2- and 3,3-derivatives, i.e. those containing the two fluorine atoms at the positions involved in the chain-shortened step, have been found to be active, the activity being similar to or lower than that displayed by the corresponding monofluorinated acids.

Synthesis of trifluoromethyl ketones as inhibitors of antennal esterases of insects

A variety of long chain aliphatic and aromatic trifluoromethyl ketones I-XIV has been conveniently prepared, many of them for the first time, from the corresponding Grignard or organolithium derivatives. Two of them, ( Z)-1,1, 1-trifluoro-15-octadecen-13-yn-2-one ( XV) and ( Z)-1,1,1-trifluoro-16-nonadecen-14-yn-2-one ( XVI), structurally-closed analogues of (Z)-13-hexadecen-11-ynylacetate, the sex pheromone of the processionary moth Thaumetopoea pityocampa, have been stereospecifically synthesized in excellent yield by a convenient new method. The procedure involves lithiation ot the corresponding iododerivative XXIX and XXX with one equivalent of tert-BuLi to obviate addition of the reagent to the enyne system. Some of the compounds have already been tested and found to be good inhibitors of antennal esterases in the Egyptian armyworm Spodoptera littoralis and the pheromone action in the processionary moth Thaumetopoea pityocampa. β-Thiotrifluoromethylketones XVII-XX, which are expected to enhance the inhibition activity of the parent ketones due to their higher hydration constants, have also been prepared in good yields,

Inhibition of antennal esterases of the egyptian armyworm Spodoptera littoralis by trifluoromethyl ketones

A series of aliphatic and aromatic trifluoromethyl ketones has been tested as inhibitors of the antennal esterases of the Egyptian armyworm Spodoptera littoralis, by evaluation of the extent of hydrolysis of [1- 3H]-( Z,E)-9, 11-tetradecadienyl acetate ( 1), a tritiated analog of the major component of the sex pheromone. The most active compounds with a long chain aliphatic structure were 3-octylthio-1,1,1-trifluoropropan-2-one ( 2) (IC 50 0.55 μM) and 1,1,1-trifluorotetradecan-2-one ( 4) (IC 50 1.16 μM). The aromatic compounds were generally less potent inhbitors than the coressponding aromatic ones, although β-naphthyltrifuloromethyl ketone ( 10) exhibited a remarkable inhibitory activity (IC 50 7.9 μM). Compounds 2, 4 and 10 exhibit a competitive inhibition with K i values of 2.51×10 −5 M, 2.98×10 −5 M and 2.49×10 −4 M, respectively. Some of the trifluoromethyl ketones tested were slow-binding inhibitors and compounds 2 and 10 are described as inhibitors of the antennal esterases of a moth for the first time.

Inhibition of a chain shortening step in the biosynthesis of the sex pheromone of the Egyptian armyworm Spodoptera littoralis

Inhibition of a chain shortening step in the biosynthetic pathway of the major component of the sex pheromone of the Egyptian armyworm Spodoptera littoralis by several fluorinated, acetylenic and cyclopropane fatty acids is reported. The compounds, structurally related to palmitic acid, have been tested in in vitro and in vivo bioassays. Among the compounds tested, dichlorocyclopropane acid 11 displayed the highest inhibition activity in vitro when mixed with [1- 14C]palmitic acid in 3:1, 5:1 and 10:1 ratios, whereas 2-bromopalmitic acid 1 appeared to be the best inhibitor in vivo (IC 50 = 3.46 × 10 −4 μmol/insect). The inhibition of methyl myristate formation is dose-dependent and, in order to evaluate the in vivo inhibition activity, a new method, based on measuring the loss of radioactive [1- 14C]acetic acid produced during the β-oxidation step, has also been developed.

Synthesis of biosynthetic inhibitors of the sex pheromone of Spodoptera littoralis. Part II: acetylenic and cyclopropane fatty acids

The synthesis of new acetylenic and cyclopropane fatty acids, as potential inhibitors of the β-oxidation step in the proposed biosynthesis of the sex pheromone of the Egyptian armyworm Spodoptera littoralis, is reported. The biological activity of the compounds has been determined by in vitro and in vivo bioassays, and among all the compounds tested, dichlorocyclopropane acid has shown the highest inhibition activity displayed so far.

Synthesis of potential inhibitors of the biosynthesis of the sex pheromone of Spodoptera littoralis. Part I: Monofluorinated fatty acids

Several monofluorinated fatty acids, structurally related to palmitic acid, have been synthesized and fully characterized for the first time and assayed as inhibitors of the β-oxidation step, in the proposed biosynthesis of the sex pheromone of the Egyptian armyworm Spodoptera littoralis. Silver fluoride, diethylaminosulfur trifluoride (DAST) and dichlorofluoromethane were used as fluorination agents in the synthesis of 2-fluoropalmitic acid. 3- and 4-fluoropalmitic acid and ( Z)-5-fluoro-4-hexadecenoic acid, respectively. Stereoselective 1,4-reduction of the conjugated fluorodienic ester with sodium dithionite has been utilized to prepare the required fluorinated intermediate ester for the synthesis of ( Z)-5-fluoro-4-hexadecenoic acid. A preliminary account of the biological activity of the synthetic compounds along with 2-bromopalmitic acid is also reported.