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At least 1,117 records · Page 62Linked to original sources
PubMed1999

Successful parasitation of locusts by entomopathogenic nematodes is correlated with inhibition of insect phagocytes.

The entomopathogenic nematodes Heterorhabditis megidis and Steinernema feltiae turned out to be successful antagonists of the orthopteran insects Locusta migratoria and Schistocerca gregaria. The death rate of locusts maintained on nematode-inoculated sand was remarkably high. Even dosages as low as one nematode per cubic centimeter of sand killed approximately 50% of the locusts within 10 days. The impact of parasitation on locusts' immune defense was closely investigated for L. migratoria parasitized by H. megidis. Adult locusts died within 30-35 h after being fed with 50 infective H. megidis juveniles. Within the first 30 h after ingestion of the nematodes, locust hemolymph was assayed for alterations in the humoral and cellular defense components and for the presence of the nematode-associated Photorhabdus luminescens bacteria. Humoral defense was generally low without any correlation to the state of parasitation. There was no detectable activity against Escherichia coli and only little lysozyme-like activity against Micrococcus luteus. In contrast, cellular defense components were strongly influenced by parasitation. Most interestingly, the phagocytic capacity of the hemocytes was already hampered 12 h after oral application of the nematodes, whereas considerable hemocyte death occurred not earlier than 24 h after feeding. The nematode-associated bacteria could be detected in hemolymph of some of the nematode-fed locusts as early as 3 h after feeding and in all hemolymph samples after 24 h. Supernatants from isolated P. luminescens cultures were able to inhibit the L. migratoria phagocytes in vitro; thus the successful parasitation appears to be dependent on an inhibition by bacteria-released compounds rather than on overloading or simply killing of the phagocytic active hemocytes.

Animals↗
PubMed1978

[Simuliids larvae microsporidans: ultrastructural data (author's transl)].

This work is the summary of our present knowledge about the ultrastructure of Simuliids larvae Microsporidans, including several new data concerning: 1. Pleistophora simulii (Lutz et Splendore, 1904): reticulated or net-like plasmodial envelope, formation of pansporoblastic structures looking like short pipes. 2. Stempellia simulii Maurand et Manier, 1968: plasmodial envelope as Pleistophora simulii, granular-textured polaroplast. 3. Thelohania fibrata (Strickland, 1913): ultrastructural study of the sporogonic sequence nerve done so far. 4. Thelohania bracteata (Stickland, 1913): its relations with Thelohania minuta, T. canningi, Amblyospora bracteata, Pegmatheca simulii. 5. Tuzetia debaisieuxi (Jirovec, 1943): formation of pseudopansporoblasts by the host-cell membrane.

Animals↗
PubMed1988

Costs of different methods to control riverine tsetse in West Africa.

Tsetse projects in several West African countries using different techniques to control or eradicate the fly were analysed in order to obtain comparable figures on the economics of the respective strategies. In the first stage the study concentrated on the control of riverine species by trapping, aerial spraying and sterile male release. First results with regard to the costs of the different methods are presented.

Africa, Western↗
PubMed1996

New insights into the mechanisms of fungal pathogenesis in insects.

Entomopathogenic fungi are attracting attention as potential biological control agents of insect pests. The mechanisms of pathogenesis have parallels with those of some plant-pathogenic fungi, particularly in the areas of formation of an infection structure, entry into the host and toxin-mediated host death. Understanding these processes will provide a rational basis for strain selection and improvement.

Animals↗
PubMed2003

Sustainability of insect resistance management strategies for transgenic Bt corn.

Increasing interest in the responsible management of technology in the industrial and agricultural sectors of the economy has been met thorough the development of broadly applicable tools to assess the "sustainability" of new technologies. An arena ripe for application of such analysis is the deployment of transgenic crops. The new transgenic pesticidal or plant-incorporated protectant (PIP) crops have seen widespread application in the United States based on the features of higher yield, lower applications of insecticides, and control of mycotoxin content. However, open rejection of these new crops in Europe and in other countries has been a surprising message and has limited their worldwide acceptance. The US Environmental Protection Agency's (USEPA) Office of Pesticide Programs (OPP) has worked on the development and analysis of insect resistance management (IRM) strategies and has mandated specific IRM requirements for Bacillus thuringiensis (Bt) crops since 1995 under the Food, Fungicide, Insecticide, and Rodenticide Act. Improvement of data quality and sustainability of IRM strategies have been targeted in an ongoing partnership between the USEPA Office of Research and Development and the Office of Pesticide Programs that will further enhance the agency's ability to develop sustainable insect resistance management strategies for transgenic field corn (Bt corn) producing B. thuringiensis (Bt) insecticidal proteins.

Animals↗
PubMed2026

Microbial allies in a cotton pest: A descriptive account of associated microbiota dynamics in Dysdercus cingulatus across development.

BACKGROUND: Hemipteran insects harbour several symbiotic partners, mainly bacteria, which play pivotal roles for hosts like dietary provision, support overall physiology, xenobiotic degradation and manipulate/regulate behaviour. Most of these symbionts usually reside and operate from the digestive tracts of the animals. Cotton is one of the major cash crops in India and Dysdercus cingulatus (D. cingulatus) though a secondary pest, is causing significant destruction of cotton bolls, poor lint quality and reduce oil content of seeds. Premature opening of cotton bolls often leads to bacterial and fungal infections, thus resulting in extensive economic loss worldwide. D. cingulatus is a hemimetabolous insect that comprises of developmental stages like egg, nymph (5 instar stages), and adult. The present work explored the ontogeny specific diversity in the associated microbiota and predicted their probable functional inputs in D. cingulatus. RESULTS: The data obtained using 16S rRNA gene sequencing (NovaSeq 6000) revealed presence of members of Proteobacteria (65.83%), Firmicutes (24%), Actinobacteria (10%) phyla throughout the ontogeny of D. cingulatus. Highest alpha diversity of these symbiotic bacteria was recorded in the third instar nymphs in contrast to rest of the developmental stages. Among all the observed genera, Stenotrophomonas, Hungatella and Glutamicibacter were predominant from egg to adult stages. MicFunPred, a tool used for predicting the probable functional inputs of these symbionts, hinted at their probable stage specific contribution in crucial biochemical pathways such as polyketide biosynthesis, ascorbate/aldarate metabolism, pentose phosphate and glyoxylate cycles, steroid hormone and peptidoglycan biosynthesis, and glycolysis/pyruvate metabolism. CONCLUSIONS: The primary investigations on the ontogenetic composition and diversity of associated microbiota, suggest dynamic shifts in D. cingulatus, concurrent with their probable functions/roles in the host development and metabolism. To the best of our knowledge, this is the first report on symbiotic microbiota variation across the developmental stages of D. cingulatus that provides preliminary descriptive observations that may guide future functional and experimental investigations into microbiota-based pest management.

Animals↗
PubMed2005

Identification and characterization of proteins from Bacillus thuringiensis with high toxic activity against the sheep blowfly, Lucilia cuprina.

Current control of the sheep blowfly (Lucilia cuprina) relies on chemical insecticides, however, with the development of resistance and increasing concerns about human health and environmental residues, alternative strategies to control this economically important pest are required. In this study, we have identified several isolates of Bacillus thuringiensis (Bt), collected from various Australian soil samples, that produce crystals containing 130 and 28 kDa proteins. These isolates were highly toxic to feeding larvae in both in vitro bioassays and in vivo on sheep. By N-terminal amino acid sequencing, we identified the smaller crystal band (28 kDa) as a cytological (Cyt) protein. Upon solubilization and proteolytic processing by trypsin, the 130 kDa crystal protein yielded among others, a truncated 55-60 kDa toxin moiety which exhibited larvicidal activity against sheep blowfly. The amino-terminal sequence of the trypsin-resistant protein band revealed that this Bt endotoxin was encoded by a new cry gene. The novel cry protein was present in all the strains that were highly toxic in the larval assay. We have also identified from one of the isolates, a novel secretory toxin with larvicidal activity.

Animals↗
PubMed2006

The efficacy of two entomopathogenic biocontrol agents against adult Thrips palmi (Thysanoptera:Thripidae).

The efficacy of the two entomopathogenic biocontrol agents, Steinernema feltiae (Filipjev) and Lecanicillium muscarium (Petch), against juvenile Thrips palmi Karny in the laboratory situation is well documented. This study investigated the extrapolation of this knowledge to the control of adult stages. S. feltiae caused significantly higher mortality to juvenile T. palmi than to adult stages, whereas L. muscarium had a more significant impact on adult stages. The potential to develop an IPM strategy to control T. palmi utilising the two entomopathogens is discussed.

Age Factors↗
PubMed2004

Larvicidal Cry proteins from Bacillus thuringiensis are released in root exudates of transgenic B. thuringiensis corn, potato, and rice but not of B. thuringiensis canola, cotton, and tobacco.

Larvicidal proteins encoded by cry genes from Bacillus thuringiensis were released in root exudates from transgenic B. thuringiensis corn, rice, and potato but not from B. thuringiensis canola, cotton, and tobacco. Nonsterile soil and sterile hydroponic solution in which B. thuringiensis corn, rice, or potato had been grown were immunologically positive for the presence of the Cry proteins; from B. thuringiensis corn and rice, the soil and solution were toxic to the larva of the tobacco hornworm (Manduca sexta), and from potato, to the larva of the Colorado potato beetle (Leptinotarsa decemlineata), representative lepidoptera and coleoptera, respectively. No toxin was detected immunologically or by larvicidal assay in soil or hydroponic solution in which B. thuringiensis canola, cotton, or tobacco, as well as all near-isogenic non-B. thuringiensis plant counterparts or no plants, had been grown. All plant species had the cauliflower mosaic virus (CaMV) 35S promoter, except rice, which had the ubiquitin promoter from maize. The reasons for the differences between species in the exudation from roots of the toxins are not known. The released toxins persisted in soil as the result of their binding on surface-active particles (e.g. clay minerals, humic substances), which reduced their biodegradation. The release of the toxins in root exudates could enhance the control of target insect pests, constitute a hazard to nontarget organisms, and/or increase the selection of toxin-resistant target insects.

Bacterial Proteins↗
PubMed2006

Mode of action of Bacillus thuringiensis Cry and Cyt toxins and their potential for insect control.

Bacillus thuringiensis Crystal (Cry) and Cytolitic (Cyt) protein families are a diverse group of proteins with activity against insects of different orders--Lepidoptera, Coleoptera, Diptera and also against other invertebrates such as nematodes. Their primary action is to lyse midgut epithelial cells by inserting into the target membrane and forming pores. Among this group of proteins, members of the 3-Domain Cry family are used worldwide for insect control, and their mode of action has been characterized in some detail. Phylogenetic analyses established that the diversity of the 3-Domain Cry family evolved by the independent evolution of the three domains and by swapping of domain III among toxins. Like other pore-forming toxins (PFT) that affect mammals, Cry toxins interact with specific receptors located on the host cell surface and are activated by host proteases following receptor binding resulting in the formation of a pre-pore oligomeric structure that is insertion competent. In contrast, Cyt toxins directly interact with membrane lipids and insert into the membrane. Recent evidence suggests that Cyt synergize or overcome resistance to mosquitocidal-Cry proteins by functioning as a Cry-membrane bound receptor. In this review we summarize recent findings on the mode of action of Cry and Cyt toxins, and compare them to the mode of action of other bacterial PFT. Also, we discuss their use in the control of agricultural insect pests and insect vectors of human diseases.

Bacillus thuringiensis↗
PubMed2002

Enzyme-linked immunofiltration assay used in the screening of solid supports and immunoreagents for the development of an azinphos-methyl flow immunosensor.

Azinphos-methyl (AM), O,O-dimethyl S-[(4-oxo-1,2,3-benzotriazin-3(4H)-yl)methyl] phosphorodithioate, is a dithiophosphorous insecticide extensively used for the control of fruit culture pests. In this work the ELIFA system, initially developed and marketed to substitute conventional ELISA methods, was used for the screening of supports and immunoreagents in the development of a flow immunosensor to AM. The objective was to find the optimal antibody concentration, support quantity and enzymatic tracer concentration to develop a sensitive and reusable immunosensor. The influence of chitosan as protein stabilizing agent was also investigated. We observed that, on the basis of immunosorbent characterization, chitosan-modified silica with immobilized LIB-MFH14 monoclonal antibody (MAb) showed the best sensitivity, with a I(50) value of 6 nM AM. All of the immobilized MAbs either in alkylaminated or chitosan-modified silica showed I(50) values between 10 and 36 nM. Regarding the regeneration capability, the best desorption agent tested was 0.1 M glycine/HCl, pH 2.0, performing in most cases a 100% desorption after just one wash and maintaining the antibody activity even after 20 cycles of regeneration. The chitosan-modified silica seemed to be the best support for this purpose.

Animals↗
PubMed1995

The susceptibility of different species of sciarid flies to entomopathogenic nematodes.

Steinernema feltiae is the most effective nematode for controlling sciarid species but S. carpocapsae does exert some control. S. feltiae is less effective at 30 degrees C than at 22 degrees C. S. anomali, S. riobravis and two Heterorhabditis spp. gave better control at the higher temperature. All six sciarid species tested were susceptible to S. feltiae but there was some variation in the level of infection. UK isolates of S. feltiae were more effective against UK sciarids than the nematode isolates from other European countries which were tested. Adult sciarids are infected by S. feltiae and can disperse nematodes to nematode-free compost.

Animals↗
PubMed1995

The effect of temperature on infection, development and reproduction of heterorhabditids.

The effect of temperature on infection, development and reproduction of five Heterorhabditis isolates was examined in Galleria mellonella larvae. Infectivity was examined at six temperatures (5, 10, 15, 20, 25 and 30 degrees C). The proportion of Galleria infected remained relatively constant, only dropping at extremes of the temperature range tested. However, the mean number of nematodes per host produced a different trend, with each isolate displaying optimal infectivity at 25 degrees C. The temperature range over which the juveniles could infect differed between the isolates. This is thought to be related to the geographic origins of the species. Development and reproduction occurred over a slightly narrower temperature range than that allowing infection to occur. Differences between the isolates at which development and reproduction occurred were noted. There were also differences in the mean number of juveniles produced per cadaver following either infection in sand (10 nematodes/larva) or the injection of one juvenile per larva, suggesting that reproduction is tightly regulated by density-dependent constraints.

Animals↗
PubMed1998

Biophysical properties of the surface of desiccation-tolerant mutants and parental strain of the entomopathogenic nematode Heterorhabditis megidis (strain UK211).

Entomopathogenic nematodes (EPN) are useful biological control agents of insect pests. However, the infective juvenile (IJ) stage which is the only stage to occur outside the host is susceptible to environmental extremes such as desiccation. We have isolated desiccation-tolerant strains of the EPN Heterorhabditis megidis. In this paper we describe the surface properties of these desiccation-tolerant mutants. Heterorhabditid IJs retain the sheath of the previous larval stage. The mutant lines possess alterations in the surface properties of the sheath. Differences were observed in fluorescent lipid analogue insertion into the surface of the sheath. Furthermore, cationized ferritin-binding studies demonstrated that the mutant lines possessed an increase in net negative surface charge. Removal of the surface layer of the sheath resulted in the loss of the mutant phenotype and in a reduction in the desiccation tolerance of the parental strain. Therefore, the negatively charged 'surface coat' appears to play an important role in the desiccation tolerance of Heterorhabditis species.

Animals↗
PubMed2004

Differentially enhanced insect resistance, at a cost, in Arabidopsis thaliana constitutively expressing a transcription factor of defensive metabolites.

A transgenic line of Arabidopsis thaliana constitutively expressing a conserved MYB transcription factor of phenylpropanoid biosynthesis resulting in solid-purple leaves had significantly increased resistance to leaf feeding by first instar fall armyworms (Spodoptera frugiperda), but no enhanced resistance to cabbage looper (Trichoplusia ni) larvae, when compared to wild type plants. However, inflorescence and silique (seed pod) production were significantly reduced by 22 and 52%, respectively, in the transgenic line compared to wild type plants. Reduction in feeding by S. frugiperda was significantly positively correlated with reduction in weights of survivors, but both were negatively correlated with the concentration of anthocyanins. These results indicate that a single gene regulator can activate a defensive pathway sufficient to produce increased resistance to insects but that this activation confers a cost in plant productivity.

Animals↗