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PubMed1997

Initial frequency of alleles for resistance to Bacillus thuringiensis toxins in field populations of Heliothis virescens.

The risk of rapid pest adaptation to an insecticide is highly dependent on the initial frequency of resistance alleles in field populations. Because we have lacked empirical estimates of these frequencies, population-genetic models of resistance evolution have relied on a wide range of theoretical estimates. The recent commercialization of genetically engineered cotton that constitutively produces an insecticidal protein derived from the biocontrol agent, Bacillus thuringiensis (Bt) has raised concern that we lack data needed to quantify the risk of insect pests such as Heliothis virescens rapidly adapting to this ecologically valuable class of toxins. By individually mating over 2,000 male H. virescens moths collected in four states to females of a Bt toxin-resistant laboratory strain, and screening F1 and F2 offspring for tolerance of the toxic protein, we were able to directly estimate the field frequency of alleles for resistance as 1.5 x 10(-3). This high initial frequency underscores the need for caution in deploying transgenic cotton to control insect pests. Our single-pair mating technique greatly increases the efficiency of detecting recessive resistance alleles. Because alleles that decrease target site sensitivity to Bt toxins and other insecticides are often recessive, this technique could be useful in estimating resistance allele frequencies in other insects exposed to transgenic insecticidal crops or conventional insecticides.

Journal Article↗
PubMed1990

Expression of cauliflower mosaic virus gene I using a baculovirus vector based upon the p10 gene and a novel selection method.

A new baculovirus expression vector based upon the p10 gene of Autographa californica nuclear polyhedrosis virus (AcNPV) and a novel system for the screening of p10 recombinants have been developed. The insertion of a cassette containing the lacZ gene under the control of a heat-shock promoter of Drosophila melanogaster downstream from the cloning site in p10 transfer vectors allows the convenient identification of putative recombinants by virtue of their expression of beta-galactosidase. Using this p10 transfer vector an AcNPV recombinant was engineered with a cDNA copy of gene I of cauliflower mosaic virus (CaMV) in place of the p10 coding sequence. This p10 recombinant expressed CaMV gene I at levels equivalent to those of p10 and polyhedrin, and was shown to be as effective in producing this protein as recombinants exploiting the polyhedrin promoter. CaMV gene I protein formed large numbers of hollow fiber-like structures in the cytoplasm of infected cells. Because the polyhedrin gene remains intact, these p10 expression vectors may be exploited for the expression of heterologous proteins in insects infected per os and for the enhancement of baculovirus pathogenicity for insect control.

Animals↗
PubMed2002

Activity of octylthiotrifluoropropan-2-one, a potent esterase inhibitor, on growth, development, and intraspecific communication in Spodoptera littoralis and Sesamia nonagrioides.

A series of experiments were conducted to examine the effect of 3-octylthio-1,1,1-trifluoro-2-propanone (OTFP) on growth, development, and behavior of the cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae), and the corn stalk borer, Sesamia nonagrioides (Lepidoptera: Noctuidae). The chemical behaved as an oviposition deterrent and, when added to the diet of the second-instar larvae of both insects, reduced diet consumption and growth, pupation, and adult emergence. Treatment of 100-5000 ng of the compound on fourth-instar larvae for 3-24 h, however, did not produce significant differences in the amount of diet ingested. Our results suggest that the effect of OTFP is long-lasting and that the inhibitor is not fully detoxified by the detoxification enzymes of the digestive tract of the insects. In behavioral assays, adult males which had been treated with the chemical at the larval stage were less attracted to the pheromone source than regular untreated males. When Sp. littoralis untreated females were used as the attractant source, treated males also displayed significantly fewer contacts with the cage-containing females than untreated or solvent-treated males. In the presence of treated females, only 27% of treated males successfully completed the flight in comparison to animals responding to solvent-treated females (54.5%). By contrast, when Se. nonagrioides females, whether they had been subjected or not to the treatment, were used as the attractant source, males were similarly attracted to them regardless of whether they had been treated or not at the larval stage. Analyses of gland extracts of Sp. littoralis treated females showed no difference from control insects in the qualitative or quantitative composition of the pheromone blend. The results obtained, in combination with other results previously reported by us (Riba, M.; Sans, A.; Bau, P.; Grolleau, G.; Renou, M.; Guerrero, A. J. Chem. Ecol. 2001, 27, 1879-1897), provide new and relevant information about the possible utility of these chemicals in future studies directed to the development of new approaches for pest control.

Acetone↗
PubMed2006

Evidence of oral toxicity of Photorhabdus temperata strain K122 against Prays oleae and its improvement by heterologous expression of Bacillus thuringiensis cry1Aa and cry1Ia genes.

Photorhabdus temperata strain K122 exhibited oral toxicity against Prays oleae with an LC50 of 58.1 x 10(6) cells ml(-1). Recombinant P. temperata strains expressing the cry1Aa and/or cry1Ia genes of Bacillus thuringiensis have been constructed. The two cry genes, encoding delta-endotoxins, were placed under the control of the lac promoter and IPTG dependent expression in P. temperata was demonstrated. The presence of the cry genes in K122 resulted in a clear improvement of oral toxicity. This improvement was of 6.2-, 6.6-, and 14.6-fold for the strains K122(pBCcry1Aa), K122(pBScry1Ia), and K122(pBCcry1Aa + pBScry1Ia), respectively. Furthermore, determination of the Synergistic Factor between Cry1Aa and Cry1Ia showed that they act synergistically. This work demonstrates that the heterologous expression of B. thuringiensis cry genes in P. temperata can be used to improve and broaden its host range for insect control.

Animals↗
PubMed1999

Eicosanoids mediate nodulation reactions to bacterial infections in adults of two 17-year periodical cicadas, Magicicada septendecim and M. cassini.

Nodulation is the first and quantitatively most important cellular defense reaction to bacterial infections in insects. Treating adults of the 17-year periodical cicadas, Magicicada septendecim and M. cassini, with eicosanoid biosynthesis inhibitors immediately prior to intrahemocoelic injections of the bacterium, Serratia marcescens, sharply reduced the nodulation response to bacterial challenges. Separate treatments with specific inhibitors of phospholipase A(2), cyclooxygenase, and lipoxygenase reduced nodulation, supporting our view that nodule formation is a multi-step process in which individual steps are separately mediated by lipoxygenase and cyclooxygenase products. The inhibitory influence of dexamethasone was apparent by 2 h after injection, and nodulation was significantly reduced, relative to control insects, over the following 14 h. The dexamethasone effects were reversed by treating bacteria-challenged insects with the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid. Low levels of arachidonic acid were detected in fat body phospholipids. These findings in adults of an exopterygote insect species with an unusual life history pattern broaden our hypothesis that eicosanoids mediate cellular immune reactions to bacterial infections in most, if not all, insects.

Journal Article↗
PubMed1999

Molecular and biochemical aspects of chitin synthesis inhibition.

Chitin, is a beta-1,4-linked aminopolysacharide homopolymer of GlcNAc that occurs as a glycoprotein in the exoskeleton of arthropods, the cell wall of fungi and in various components of diverse invertebrates. It is synthesized in two different ways: in fungi the chitin synthase enzyme occurs as an inactive zymogen in vesicles called chitosomes and requires proteolytic activation; in arthropods this enzyme is membrane-bound and catalyzes the addition of GlcNAc units to a dolichol carrier. Chitin is degraded by three different chitinases, the endochitinase that degrades chitin into oligosaccharides of differing chain lengths, the exochitinase that degrades oligosaccharides into diacetylchitobiose and chitobiase, which degrades diacetylchitobiose into GlcNAc monomers. Inhibition of chitin synthesis as well as degradation can both result in deleterious effects that are often similar. Chitin synthesis can be blocked during the various steps by a variety of antibiotics, metabolic inhibitors, insect growth regulators, alkaloids and hormone analogs. During the molting process in arthropods, genes are sequentially expressed and repressed by developmental hormones. When these hormones or their analogs are administered temporally out of sequence, it can result in the blocking of cuticle formation, including chitin synthesis. With the advent of biotechnology and the availability of both complementary DNA and antibody probes, it is possible to develop high throughput assays for discovering new chemicals that can block chitin formation. Chitin synthesis inhibitors as well as inhibitors of chitin degradation that produce similar effects are promising agents for controlling insect pests, fungal pathogens and helminthic parasites.

Animals↗
PubMed2001

[Search for the spirochete Borrelia burgdorferi sensu lato by polymerase chain reaction in wild Chilean ticks].

BACKGROUND: Lyme disease is a tick-borne human disease caused by the spirochete Borrelia burgdorferi. Main vectors of Lyme disease are ticks of the Ixodes and Amblyomma genera. Cases with clinical manifestations of Lyme disease and favorable responses to antimicrobial agents have been reported in Chile, some of them with erythema migrans, the hallmark of B burgdorferi infection. AIM: To detect the presence of B burgdorferi in Chilean ticks. MATERIAL AND METHODS: A total of 62 ticks were recollected from wild rodents and cervidae in the Southern region of Chile. Infected and non infected ticks of the species Ixodes ricimus, were used as controls. Insects were homogenised and B burgdorferi was detected using classical and nested polymerase chain reactions. RESULTS: B burgdorferi was not detected in the studied ticks. CONCLUSIONS: Although all the elements required for the enzootic cycle of B burgdorferi are present in Chile, its direct detection in Chilean ticks using the nested polymerase chain reaction assay was negative.

Animals↗
PubMed2000

Insect cellular reactions to the lipopolysaccharide component of the bacterium Serratia marcescens are mediated by eicosanoids.

Nodulation, which begins with the formation of cellular microaggregates, is the predominant cellular defense reaction to bacterial infections in insects. We suggested that these reactions to bacterial infections are mediated by eicosanoids. The lipopolysaccharide (LPS) component of some bacterial cells stimulates defense reactions in mammals and insects. Here, we report on experiments designed to test the hypothesis that eicosanoids mediate microaggregation reactions to LPS. Injections of LPS (purified from the bacterium, Serratia marcescens) into larvae of the tenebrionid beetle, Zophobas atratus, stimulated microaggregation reactions in a dose-dependent manner. Treatments with eicosanoid-biosynthesis inhibitors immediately prior to LPS challenge sharply reduced the microaggregation responses. Separate treatments with specific inhibitors of phospholipase A(2), cyclooxygenase and lipoxygenase reduced microaggregation, supporting our view that microaggregate formation involves lipoxygenase and cyclooxygenase products. The inhibitory influence of dexamethasone was apparent within 30min after injection, and microaggregation was significantly reduced, relative to control insects, over the following 90min. The dexamethasone effects were reversed by treating LPS-injected insects with the eicosanoid precursor, arachidonic acid. These findings indicate that cellular defense reactions to a specific component of bacterial cells are mediated by eicosanoids, and open up new possibilities for dissecting detailed hemocytic actions in insect immune reactions to bacterial infections.

Journal Article↗
PubMed2006

A Bacillus thuringiensis S-layer protein involved in toxicity against Epilachna varivestis (Coleoptera: Coccinellidae).

The use of Bacillus thuringiensis as a biopesticide is a viable alternative for insect control since the insecticidal Cry proteins produced by these bacteria are highly specific; harmless to humans, vertebrates, and plants; and completely biodegradable. In addition to Cry proteins, B. thuringiensis produces a number of extracellular compounds, including S-layer proteins (SLP), that contribute to virulence. The S layer is an ordered structure representing a proteinaceous paracrystalline array which completely covers the surfaces of many pathogenic bacteria. In this work, we report the identification of an S-layer protein by the screening of B. thuringiensis strains for activity against the coleopteran pest Epilachna varivestis (Mexican bean beetle; Coleoptera: Coccinellidae). We screened two B. thuringiensis strain collections containing unidentified Cry proteins and also strains isolated from dead insects. Some of the B. thuringiensis strains assayed against E. varivestis showed moderate toxicity. However, a B. thuringiensis strain (GP1) that was isolated from a dead insect showed a remarkably high insecticidal activity. The parasporal crystal produced by the GP1 strain was purified and shown to have insecticidal activity against E. varivestis but not against the lepidopteran Manduca sexta or Spodoptera frugiperda or against the dipteran Aedes aegypti. The gene encoding this protein was cloned and sequenced. It corresponded to an S-layer protein highly similar to previously described SLP in Bacillus anthracis (EA1) and Bacillus licheniformis (OlpA). The phylogenetic relationships among SLP from different bacteria showed that these proteins from Bacillus cereus, Bacillus sphaericus, B. anthracis, B. licheniformis, and B. thuringiensis are arranged in the same main group, suggesting similar origins. This is the first report that demonstrates that an S-layer protein is directly involved in toxicity to a coleopteran pest.

Amino Acid Sequence↗
PubMed1994

Do bedbugs transmit hepatitis B?

An intervention study was done over two years in seven Gambian villages to determine the contribution of bedbugs to hepatitis B transmission. In addition, fortnightly questionnaires were completed for each child to assess other possible routes of transmission. The intervention, insecticide spraying of the child's dwelling, was highly effective in reducing exposure to bedbugs but there was no effect on hepatitis B infection. No other risk factor for transmission was identified despite a consistent village-to-village variation in the rate of childhood infection. The major mode of transmission of hepatitis B in childhood remains unknown.

Animals↗
PubMed1994

Monitoring resistance gene frequencies in Malaysian Culex quinquefasciatus Say adults using rapid non-specific esterase enzyme microassays.

The ability to identify the occurrence of different resistance genotypes in field populations of mosquito is considered important for the purpose of optimising chemical control operations. The recent development of rapid microassays of enzymes responsible for resistance has provided a means for rapidly assessing the genetic background of target mosquito populations. This concept is the topic of investigation in this study. Non-specific esterase activity, which is responsible for the resistance to organophosphates in Malaysian Culex quinquefasciatus Say adults, was determined in 3 field populations from Kuala Lumpur City using rapid enzyme assay. The optical density results were used to estimate the genotypic frequencies of the populations. Subsequently, time-dependent changes in the various frequencies were determined. Such techniques allowed rapid assessment of resistance genotypes for decision-making and its possible use in insect control merits further investigation.

Animals↗
PubMed2003

Long-term regional suppression of pink bollworm by Bacillus thuringiensis cotton.

Despite the potentially profound impact of genetically modified crops on agriculture and the environment, we know little about their long-term effects. Transgenic crops that produce toxins from Bacillus thuringiensis (Bt) to control insects are grown widely, but rapid evolution of resistance by pests could nullify their benefits. Here, we present theoretical analyses showing that long-term suppression of pest populations is governed by interactions among reproductive rate, dispersal propensity, and regional abundance of a Bt crop. Supporting this theory, a 10-year study in 15 regions across Arizona shows that Bt cotton suppressed a major pest, pink bollworm (Pectinophora gossypiella), independent of demographic effects of weather and variation among regions. Pink bollworm population density declined only in regions where Bt cotton was abundant. Such long-term suppression has not been observed with insecticide sprays, showing that transgenic crops open new avenues for pest control. The debate about putative benefits of Bt crops has focused primarily on short-term decreases in insecticide use. The present findings suggest that long-term regional pest suppression after deployment of Bt crops may also contribute to reducing the need for insecticide sprays.

Animals↗
PubMed2001

c-Myc regulates mammalian body size by controlling cell number but not cell size.

Overexpression of the proto-oncogene c-myc has been implicated in the genesis of diverse human tumours. c-Myc seems to regulate diverse biological processes, but its role in tumorigenesis and normal physiology remains enigmatic. Here we report the generation of an allelic series of mice in which c-myc expression is incrementally reduced to zero. Fibroblasts from these mice show reduced proliferation and after complete loss of c-Myc function they exit the cell cycle. We show that Myc activity is not needed for cellular growth but does determine the percentage of activated T cells that re-enter the cell cycle. In vivo, reduction of c-Myc levels results in reduced body mass owing to multiorgan hypoplasia, in contrast to Drosophila c-myc mutants, which are smaller as a result of hypotrophy. We find that c-myc substitutes for c-myc in fibroblasts, indicating they have similar biological activities. This suggests there may be fundamental differences in the mechanisms by which mammals and insects control body size. We propose that in mammals c-Myc controls the decision to divide or not to divide and thereby functions as a crucial mediator of signals that determine organ and body size.

Animals↗
PubMed2005

Identification of a novel prothoracicostatic hormone and its receptor in the silkworm Bombyx mori.

The insect brain regulates the activity of the prothoracic glands to secrete ecdysteroids, which affect growth, molting, and metamorphosis. Here we report the identification of a novel prothoracicostatic factor and its receptor in the silkworm Bombyx mori. The prothoracicostatic factor purified from pupal brains of B. mori is a decapeptide with the conserved structure of an insect myosuppressin and thus named Bommo-myosuppressin. Bommo-myosuppressin dose dependently suppressed the cAMP level and inhibited ecdysteroidogenesis in the larval prothoracic glands at much lower concentrations than the prothoracicostatic peptide, the other prothoracicostatic factor reported previously. In vitro analyses using a prothoracic gland incubation method revealed that Bommo-myosuppressin and prothoracicostatic peptide regulate the prothoracic gland activity via different receptors. In situ hybridization and immunohistochemistry revealed the existence of Bommo-myosuppressin in the brain neurosecretory cells projecting to neurohemal organs in which it is stored. We also identified and functionally characterized a specific receptor for Bommo-myosuppressin and showed its high expression in the prothoracic glands. All these results suggest that Bommo-myosuppressin functions as a prothoracicostatic hormone and plays an important role in controlling insect development.

Amino Acid Sequence↗
PubMed2006

The prey-dependent consumption two-prey one-predator models with stage structure for the predator and impulsive effects.

In this paper, we consider the prey-dependent consumption two-prey one-predator models with stage structure for the predator and impulsive effects. By applying the Floquet theory of linear periodic impulsive equation, we show that there exists a globally asymptotically stable pest-eradication periodic solution when the impulsive period is less than some critical value, that is, the pest population can be eradicated totally. But from the point of ecological balance and saving resources, we only need to control the pest population under the economic threshold level instead of eradicating it totally, and thus, we further prove that the system is uniformly permanent if the impulsive period is larger than some critical value, and meanwhile we also give the conditions for the extinction of one of the two preys and permanence of the remaining species. Thus, we can use the stability of the positive periodic solution and its period to control insect pests at acceptably low levels. Considering population communities always are imbedded in periodically varying environments, and the parameters in ecosystem models may oscillate simultaneously with the periodically varying environments, we add a forcing term into the prey population's intrinsic growth rate. The resulting bifurcation diagrams show that with the varying of parameters, the system experiences process of cycles, periodic windows, periodic-doubling cascade, symmetry breaking bifurcation as well as chaos.

Animals↗
PubMed2025

Multi-omics reveals an ecdysone-activated Eip75B-FABP signaling axis coordinating nutrient metabolism for development in Hermetia illucens.

INTRODUCTION: Efficient nutrient storage is essential for insect development and energy homeostasis; however, the mechanisms coordinating nutrient allocation during ontogeny are not well understood. Elucidating these systems may yield valuable insights to insect metabolic adaptation. OBJECTIVES: This study aimed to identify regulatory modules governing nutrient metabolism in insects, focusing on hormonal and metabolic interplay. METHODS: Multi-omics profiling (proteomics, phosphoproteomics, and transcriptomics) was conducted throughout the life cycle, from egg to adult, to identify metabolic regulators. RNAi was utilized for gene knockdown, followed by qRT-PCR and mitochondrial DNA quantification to evaluate knockdown efficiency and its metabolic implications. Assessments of nutrient metabolism were performed using assays for triglycerides, crude protein, and fatty acid synthase. EMSA and BODIPY staining examined transcriptional regulation and lipid droplet dynamics. RESULTS: Utilizing an integrative multi-omics approach, this study elucidates the temporal metabolic regulators in insects. A conserved regulatory module was identified in which the PPAR homolog, ecdysone-induced protein 75B (Eip75B), functions as a transcriptional activator of fatty acid binding protein (FABP), sustaining lipid metabolic homeostasis during the larval stage. PPARγ modulators (rosiglitazone and GW9662) alter lipid accumulation, along with the expression of Eip75B and FABP, which was measured by qRT-PCR. Furthermore, the deficiency of FABP may reprogram metabolic pathways by inhibiting lipid storage and promoting mitochondrial β-oxidation, as supported by increased mitochondrial DNA copy number, as well as enhancing protein synthesis. This metabolic change could be modulated by ecdysone signaling, as hormonal supplementation effectively rescued the lipid loss phenotype. Our results establish the ecdysone-Eip75B-FABP signaling axis as a central regulatory module that integrates hormonal and nutrient-sensing signals to control insect nutritional metabolism. CONCLUSION: The ecdysone-Eip75B-FABP axis integrates hormonal and nutrient signals to regulate metabolic plasticity, underscoring a universal strategy for developmental energy allocation. The data also offer potential implications for research on metabolic disorders and bioenergy applications.

Animals↗
PubMed1996

Molecular cloning and function expression of a diuretic hormone receptor from the house cricket, Acheta domesticus.

Insect diuretic hormones regulate fluid and ion secretion and the receptors with which they interact are attractive targets for new insect control agents. Recently, a diuretic hormone receptor from the moth Manduca sexta was isolated by expression cloning and found to be a member of the calcitonin/secretin/corticotropin releasing factor family of G-protein coupled receptors [Reagan J. D. (1994) J. Biol. Chem. 269, 9-12]. Degenerate oligonucleotides were designed based upon conserved regions in this receptor family and used to isolate a diuretic hormone receptor from the house cricket, Acheta domesticus. The complementary DNA isolated encodes a protein consisting of 441 amino acids with seven putative membrane spanning regions. Interestingly, unlike the M. sexta diuretic hormone receptor, the cricket diuretic hormone receptor contains a putative signal sequence. The receptor shares 53% and 38% sequence identity with the M. sexta diuretic hormone and human corticotropin releasing factor receptors respectively. When expressed in COS-7 cells, the receptor binds A. domesticus diuretic hormone with high affinity and stimulates adenylate cyclase with high potency. Four other insect diuretic hormones are considerably less effective at stimulating adenylate cyclase in COS-7 cells transfected with the receptor. This is in contrast to the M. sexta diuretic hormone receptor which is stimulated by all five insect diuretic hormones with high potency.

Amino Acid Sequence↗