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PubMed1995

Chaos: a potential problem in the biological control of insect pests.

Erratic variations are normally observed in the populations of insect pests that destroy crop plants. To establish a scientific basis for developing effective control procedures, we have developed a model system for the European Corn Borer (ECB) (Ostrinia nubilalis) for which extensive field data, as well as laboratory results, have been accumulated during the past four decades. The model includes both a natural ECB pathogen and a genetically engineered toxin-producing agent as possible means of biological control. Our aim was to determine the conditions that could cause the population to vary erratically, as observed in the field. The erratic behavior in our simulations was analyzed to determine whether it is chaotic; chaos is a distinct type of erratic behavior which shows extreme sensitivity to initial conditions, i.e., the starting size of the population. Our simulations show that an increase in the death rate of the infected ECB, or a decrease in the birth rate of uninfected ECBs from infected ones, variables that are known to be affected by weather conditions, can induce a chaotic regime in which ECB population peaks reach values far higher than before chaos set in. Population peaks are even greater in the presence of both biological control agents. The results show that a biological control regime cannot be effective under conditions that induce chaotic population dynamics. Microcosm studies could be used to determine whether this situation would occur in the field.

Animals↗
PubMed2000

Calcofluor disrupts the midgut defense system in insects.

The insect midgut is generally lined with a unique protective chitin/protein structure, the peritrophic membrane (PM). We demonstrated that in Trichoplusia ni larvae, the majority of PM proteins were assembled with chitin as a consequence of their chitin binding properties. These proteins could be dissociated from the PM in vitro by Calcofluor, a well-known chemical with chitin binding properties. The chitin binding characteristics of PM proteins were confirmed by their high affinity binding in vitro to regenerated chitin. In vivo assays demonstrated that Calcofluor could inhibit PM formation in five lepidopteran insects tested. The inhibition of T. ni PM formation by Calcofluor, was accompanied by increased larval susceptibility to baculovirus infection. Continuous inhibition of PM formation by Calcofluor resulted in retarded larval development and mortality. The destructive effect of Calcofluor on PM formation was demonstrated to be transient and reversible depending on the presence of Calcofluor within the midgut. In addition, degradation of the insect intestinal mucin was observed concurrently with the inhibition of PM formation by Calcofluor. Our studies revealed a potential novel approach to develop strategies for insect control by utilizing chitin binding molecules to specifically target PM formation in a broad range of insect pest species.

Animals↗
PubMed2003

Suppression of the prophenoloxidase system in Rhodnius prolixus orally infected with Trypanosoma rangeli.

Investigations were carried out to compare aspects of the prophenoloxidase (proPO)-activating pathway in Rhodnius prolixus hemolymph in response to oral infection and inoculation of the insects with two developmental forms of Trypanosoma rangeli epimastigotes strain H14. In vivo experiments demonstrated that in control insects fed on uninfected blood, inoculation challenge with short epimastigotes resulted in high phenoloxidase (PO) activity. In contrast, previous feeding on blood containing either short or long epimastigotes was able to suppress the proPO activation induced by thoracic inoculation of the short forms. In vitro assays in the presence of short epimastigotes demonstrated that control hemolymph or hemolymph provided by insects previously fed on blood containing epimastigotes incubated with fat body homogenates from control insects significantly increased the PO activity. However, fat body homogenates from insects previously fed on blood containing epimastigotes, incubated with hemolymph taken from insects fed on control blood or blood infected with epimastigotes, drastically reduced the proPO activation. The proteolytic activity in the fat body homogenates of control insects was significantly higher than in those obtained from fat body extracts of insects previously fed on blood containing epimastigotes. These findings indicate that the reduction of the proteolytic activities in the fat body from insects fed on infected blood no longer allows a significant response of the proPO system against parasite challenge. It also provides a better understanding of T. rangeli infection in the vector and offer novel insights into basic immune processes in their invertebrate hosts.

Animals↗
PubMed1995

Immunological strategies for control of insect disease vectors: a critical assessment.

Insect-borne diseases are one of the major causes of disease and death in the tropical world. Conventional methods of disease control have proven insufficient and there is pressing need for devising new strategies. One approach that has been explored by several laboratories is to compromise vector fecundity and survivorship through the immunization of vertebrate hosts with the vector's internal organs (concealed antigens). Here, Marcelo Jacobs-Lorena and Francisco J.A. Lemos critically review the results obtained to date by use of this approach. It appears that the published work is less rigorous than would be desirable and the results are contradictory. In contrast to the successes obtained with a similar immunization strategy implemented for tick-borne diseases, it is not yet clear whether or not such an approach can be applied to insect-borne diseases.

Journal Article↗
PubMed1999

Insect and arachnid hypersensitivity.

Insect hypersensitivity reactions can have a large number of clinical presentations. The majority of reactions are pruritic and involve the short- or sparsely haired areas of the body. Most are associated with eosinophilic infiltration into the skin, often in a perivascular pattern. The diagnosis may be based on compatible clinical signs and improvement with aggressive insect control and, in some cases, confirmation via provocative exposure. Intradermal, prick, or serum testing for allergen-specific IgE can be used to document the presence of reaginic antibodies against insect allergens. Treatments include avoidance, aggressive insect control, and symptomatic support; in some cases, immunotherapy may be useful in decreasing the severity of clinical reactions to insects.

Animals↗
PubMed1997

Prolonged pheromonotropic activity of pseudopeptide mimics of insect pyrokinin neuropeptides after topical application or injection into a moth.

Amphiphilic pseudopeptide analogs of Phe-Thr-Pro-Arg-Leu-NH2, representing the active C-terminal core pentapeptide of the pyrokinin class of insect neuropeptides, were synthesized by replacement of phenylalanine with hydrocinnamic acid (Hca-Thr-Pro-Arg-Leu-NH2), or addition of 1-pyrenebutyric acid (Pba-Phe-Thr-Pro-Arg-Leu-NH2) or 9-fluoreneacetic acid (Fla-Phe-Thr-Pro-Arg-Leu-NH2). The pseudopeptides were found to stimulate sex pheromone biosynthesis when injected into females of the moth Heliothis virescens. Optimal pheromonotropic responses were obtained by injection of 0.25 pmol of Hca-Thr-Pro-Arg-Leu-NH2, 2.5 pmol of Pba-Thr-Pro-Arg-Leu-NH2 and 0.5 pmol of Fla-Thr-Pro-Arg-Leu-NH2. Topical application of each of the pseudopeptides in water to the cuticle of moths stimulated significant production of pheromone at a dose of 50 pmol with optimal stimulation occurring when 500 pmol were applied. The parent peptide, Phe-Thr-Pro-Arg-Leu-NH2, failed to stimulate significant production of pheromone when applied topically at a dose as high as 2000 pmol. Temporal studies indicated that Hca-Thr-Pro-Arg-Leu-NH2 stimulated significant production of pheromone for only 4 h after application where as continuous pheromone production for 18 h was observed when either Pba-Phe-Thr-Pro-Arg-Leu-NH2 or Fla-Phe-Thr-Pro-Arg-Leu-NH2 were applied to the abdomen. The results show that modification of the C-terminal active core of the insect pyrokinins, by addition of hydrophobic moieties, can result in production of pseudopeptides which effectively penetrate the insect cuticle and have prolonged physiological effects making them favorable candidates for use in development of alternative strategies for pest insect control.

Acetates↗
PubMed2006

Genetically modified baculoviruses: a historical overview and future outlook.

The concept of using genetic engineering to improve the natural insecticidal activity of baculoviruses emerged during the 1980s. Both academic and industrial laboratories have since invested a great deal of effort to generate genetically modified (GM) or recombinant baculoviruses with dramatically improved speeds of kill. Optimal production methodologies and formulations have also been developed, and the safety and ecology of the recombinant baculoviruses have been thoroughly investigated. Unfortunately, the initial excitement that was generated by these technologies was tempered when industry made a critical decision to not complete the registration process of GM baculoviruses for pest insect control. In this chapter, we summarize the developments in the field from a historical perspective and provide our opinions as to the current status and future potential of the technology. We will argue that GM baculoviruses are valuable and viable tools for pest insect control both alone and in combination with wild-type viruses. We believe that these highly effective biopesticides still have a bright future in modern agriculture as public awareness and acceptance of GM organisms, including GM baculoviruses, increases.

Animals↗
PubMed1996

Transgenic Indica rice breeding line IR58 expressing a synthetic cryIA(b) gene from Bacillus thuringiensis provides effective insect pest control.

The Indica rice breeding line IR58 was transformed by particle bombardment with a truncated version of a synthetic cryIA(b) gene from Bacillus thuringiensis. This gene is expressed under control of the CaMV 35S promoter and allows efficient production of the lepidopteran specific delta-endotoxin. R0, R1 and R2 generation plants displayed a significant insecticidal effect on several lepidopterous insect pests. Feeding studies showed mortality rates of up to 100% for two of the most destructive insect pests of rice in Asia, the yellow stem borer (Scirpophaga incertulas) and the striped stem borer (Chilo suppressalis), and feeding inhibition of the two leaffolder species Cnaphalocrocis medinalis and Marasmia patnalis. Introduction of stem borer resistance into the germplasm of an Indica rice breeding line now makes this agronomically important trait available for conventional rice breeding programs.

Animals↗
PubMed1985

Laboratory evaluation of controlled-release insect repellent formulations.

Seven microcapsule formulations and two polymer formulations of deet were tested on white rabbits for their repellency against the mosquito, Aedes aegypti. Two microcapsule formulations and one polymer formulation provided more than 80% protection for 12 hours. Results demonstrated that the protection period of deet can be extended through controlled-release techniques.

Administration, Cutaneous↗
PubMed2004

The extracellular constitutive production of chitin deacetylase in Metarhizium anisopliae: possible edge to entomopathogenic fungi in the biological control of insect pests.

The possible contribution of extracellular constitutively produced chitin deacetylase by Metarhizium anisopliae in the process of insect pathogenesis has been evaluated. Chitin deacetylase converts chitin, a beta-1,4-linked N-acetylglucosamine polymer, into its deacetylated form chitosan, a glucosamine polymer. When grown in a yeast extract-peptone medium, M. anisopliae constitutively produced the enzymes protease, lipase, and two chitin-metabolizing enzymes, viz. chitin deacetylase (CDA) and chitosanase. Chitinase activity was induced in chitin-containing medium. Staining of 7.5% native polyacrylamide gels at pH 8.9 revealed CDA activity in three bands. SDS-PAGE showed that the apparent molecular masses of the three isoforms were 70, 37, and 26 kDa, respectively. Solubilized melanin (10microg) inhibited chitinase activity, whereas CDA was unaffected. Following germination of M. anisopliae conidia on isolated Helicoverpa armigera, cuticle revealed the presence of chitosan by staining with 3-methyl-2-benzothiazoline hydrazone. Blue patches of chitosan were observed on cuticle, indicating conversion of chitin to chitosan. Hydrolysis of chitin with constitutively produced enzymes of M. anisopliae suggested that CDA along with chitosanase contributed significantly to chitin hydrolysis. Thus, chitin deacetylase was important in initiating pathogenesis of M. anisopliae softening the insect cuticle to aid mycelial penetration. Evaluation of CDA and chitinase activities in other isolates of Metarhizium showed that those strains had low chitinase activity but high CDA activity. Chemical assays of M. anisopliae cell wall composition revealed the presence of chitosan. CDA may have a dual role in modifying the insect cuticular chitin for easy penetration as well as for altering its own cell walls for defense from insect chitinase.

Amidohydrolases↗