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At least 721 records · Page 40Linked to original sources
PubMed1997

Reversal of low-level resistance to Bacillus sphaericus in a field population of the southern house mosquito (Diptera:Culicidae) from an urban area of Recife, Brazil.

A larval population of Culex quinquefasciatus Say from an urban area (Coque) of Recife, Brazil, submitted to selection with Bacillus sphaericus Neide for a 26-mo trial, was 10 times less susceptible to B. sphaericus and slightly more susceptible to Bacillus thuringiensis israelensis, compared with untreated populations. The low-level resistance to B. sphaericus was unstable in the absence of selection pressure. The LC50 of B. sphaericus to the Coque population declined gradually and attained a susceptibility level similar to that observed in a laboratory control colony 16 mo after the treatment period was interrupted. In parallel to the recovery of B. sphaericus susceptibility. Coque larvae also were as susceptible as laboratory larvae to B. thuringiensis israelensis.

Animals↗
PubMed2003

Novel fermentation media for production of Bacillus thuringiensis subsp. israelensis.

The production of Bacillus thuringiensis subsp. israelensis (deBarjac) (Bti) as a biopesticide is not cost-effective using existing fermentation technology. In this study, we explored the use of several less expensive alternative culture media (potato, common sugar, and Bengal gram) for the growth and production of Bti. Growth was obtained in all tested media and was comparable to that obtained in conventional medium (Luria-Bertani). Toxicity assays showed that the toxin produced from the novel growth media were effective in killing larvae of Culex quinquefasciatus, Anopheles stephensi, and Aedes aegypti and toxicity was comparable to that produced from Luria-Bertani medium. These observations suggest that potato can be used as a cheap source of culture medium for the production of Bti toxin in mosquito control programs.

Aedes↗
PubMed2003

Augmentative releases of Metaphycus sp. nr flavus against citricola scale on oranges in the San Joaquin Valley of California: are early releases better than late ones?

We conducted an augmentative release trial with the encyrtid parasitoid Metaphycus sp. nr flavus (Howard) against citricola scale, Coccus pseudomagniolarum (Kuwana), in three citrus orchards in the San Joaquin Valley of California. Three parasitoid release timings (14 October-13 November, 4 January-5 February, and 26 February-16 March; hereinafter "early," "intermediate," and "late") were compared with a no-release check. Approximately 2,400 female parasitoids were released per central release tree. Late releases were associated with reduced scale survival on the release trees but no evidence of scale suppression was found on adjacent trees. Early and intermediate releases resulted in less pronounced scale suppression than late releases. Intermediate and late, but not early, releases were associated with an increase in the numbers of recovered female M. sp. nr flavus. Early releases, however, increased the numbers of recovered male Metaphycus spp. Thus, at the time of early releases, the scales may have been too small for the production of female parasitoids. A multiple regression model relating the degree of scale mortality in one orchard to the levels of recovered female Metaphycus helvolus (Compere), M. sp. nr flavus, or M. luteolus (Timberlake) (these latter two species are morphologically indistinguishable), and Coccophagus spp., suggested that the number of Coccophagus spp. females followed by M. helvolus females, were most strongly associated with scale mortality.

Animals↗
PubMed2004

Cross-resistance of Cry1Ab-selected Ostrinia nubilalis (Lepidoptera: Crambidae) to Bacillus thuringiensis delta-endotoxins.

Corn plants expressing the toxin from Bacillus thuringiensis (Berliner) have proven to be effective in controlling lepidopteran pests such as the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae). Several Bt toxins are being tested and incorporated into crop genomes, although tests for cross-resistance among different toxins have been limited by a lack of resistant colonies. Four different colonies of O. nubilalis selected with full-length Cry1Ab incorporated into artificial diet developed significant levels of resistance (2.0- to 10-fold) within 10 generations. Additionally, selection with Cry1Ab resulted in decreased susceptibility to a number of other toxins to which the selected colonies were not previously exposed. Significantly, levels of resistance were highest to Cry1Ac with resistance ratios up to 51.0-fold. Low levels (less than five-fold) of cross-resistance were detected with Cry1F. In contrast, Cry9C susceptibility was unaffected by selection with Cry1Ab. These results indicate that the availability of multiple toxins could improve resistance management strategies, provided cross-resistance among toxins is not a factor.

Animals↗
PubMed2004

Infection and pathogenicity of the mosquito densoviruses AeDNV, HeDNV, and APeDNV in Aedes aegypti mosquitoes (Diptera: Culicidae).

These studies compared three genetically distinct mosquito densoviruses Aedes aegypti (AeDNV), Hemagogus equinus (HeDNV), and Aedes Peruvian (APeDNV) densoviruses in a laboratory investigation to begin to evaluate their potential as mosquito control agents. A real-time polymerase chain reaction (PCR) assay for quantification of viral genomes and a standardized mosquito infection protocol were developed. Mortality associated with exposure to AeDNV increased in a dose-dependent manner, with the maximum mortality of 75.1% occurring in those organisms exposed to the highest dose of virus. The majority of death occurred as larvae. Similar results were observed with AeDNV produced from ground larvae and AeDNV produced from cell culture. Exposure of mosquitoes to HeDNV and APeDNV resulted in lower mortality, with values peaking at 33.5% for HeDNV and 27.8% for APeDNV. AeDNV-exposed larvae develop at a slower rate than nonexposed and HeDNV- and APeDNV-exposed larvae. Decreased virulence does not reflect a decrease in virus replication. PCR analysis of infectivity rates and titers in adults revealed reproduction of all three viruses, with an average viral titer of approximately 10 logs/mosquito after exposure to the highest dose of each virus. Accumulation of virus in the larval-rearing water was also observed with values approaching 10-11 logs/ml for each virus. These data indicate that there are dramatic differences in the pathogenicity among mosquito densoviruses.

Aedes↗
PubMed2005

Influence of three resistance sources in winter wheat derived from TAM 107 on yield response to Russian wheat aphid.

A study to determine yield response to the Russian wheat aphid, Diuraphis noxia (Mordvilko), was conducted during the 1997-1998 and 1998-1999 growing seasons at three eastern Colorado locations, Akron, Fort Collins, and Lamar, with three wheat lines containing either Russian wheat aphid-resistant Dn4 gene, Dn6 gene, or resistance derived from PI 222668, and TAM 107 as the susceptible control. Russian wheat aphids per tiller were greater on TAM 107 than the resistant wheat lines at the 10x infestation level at Fort Collins and Akron in 1999. Yield, seed weight, and number of seeds per spike for each wheat line were somewhat affected by Russian wheat aphid per tiller mainly at Fort Collins. The infested resistant wheat lines harbored fewer Russian wheat aphids and yielded more than the infested susceptible wheat lines. Wheat lines containing the Dn4, Dn6, and PI 222668 genes contain different levels of antibiosis or antixenosis and tolerance. Although differences existed among sites and resistance, there is a benefit to planting resistant wheat when there is a potential for Russian wheat aphid infestations.

Animals↗
PubMed2004

Entomopathogenic fungi for mosquito control: a review.

Fungal diseases in insects are common and widespread and can decimate their populations in spectacular epizootics. Virtually all insect orders are susceptible to fungal diseases, including Dipterans. Fungal pathogens such as Lagenidium, Coelomomyces and Culicinomyces are known to affect mosquito populations, and have been studied extensively. There are, however, many other fungi that infect and kill mosquitoes at the larval and/or adult stage. The discovery, in 1977, of the selective mosquito-pathogenic bacterium Bacillus thuringiensis Berliner israelensis (Bti) curtailed widespread interest in the search for other suitable biological control agents. In recent years interest in mosquito-killing fungi is reviving, mainly due to continuous and increasing levels of insecticide resistance and increasing global risk of mosquito-borne diseases. This review presents an update of published data on mosquito-pathogenic fungi and mosquito-pathogen interactions, covering 13 different fungal genera. Notwithstanding the potential of many fungi as mosquito control agents, only a handful have been commercialized and are marketed for use in abatement programs. We argue that entomopathogenic fungi, both new and existing ones with renewed/improved efficacies may contribute to an expansion of the limited arsenal of effective mosquito control tools, and that they may contribute in a significant and sustainable manner to the control of vector-borne diseases such as malaria, dengue and filariasis.

Animals↗
PubMed1997

Resistance to Bacillus sphaericus involves different mechanisms in Culex pipiens (Diptera:Culicidae) larvae.

Field Culex pipiens pipiens (L.) mosquitoes that were collected after a control failure with Spherimos in southern France developed high resistance (> 10,000-fold) to Bacillus sphaericus crystal toxin after < 8 generations of laboratory selection. We show that this resistance is encoded by a single major recessive gene on linkage group I at 22.1 recombination units from the sex locus, and that it is not associated with any loss of binding affinity between brush border membrane fractions and the B. sphaericus radiolabeled toxin. Thus, in Southern France, resistance differs from the high B. sphaericus resistance developed after laboratory selection of Californian C. p. quinquefasciatus. This demonstrates that at least 2 different mechanisms may confer high levels of resistance to B. sphaericus crystal toxin in mosquitoes of the C. pipiens complex. These results have important implications for mosquito control strategies.

Animals↗
PubMed1998

Field evaluation of Mesocyclops longisetus (Copepoda: Cyclopoidea) for the control of larval Aedes aegypti (Diptera Culicidae) in northeastern Mexico.

Field trials of the predacious copepod Mesocyclops longisetus Thiubaud were conducted in northeastern Mexico to determine the effectiveness of this species to control larval Aedes aegypti (L.) populations and to survive and reproduce in nature. Groups of 200, 50, and 50 ovigerous M. longisetus females were inoculated into 200-liter metal drums, discarded tires, and cemetery flower vases, respectively, which are 3 of the more important Aedes breeding sites in this area. Larvae were sampled at 15-d intervals, and total surviving cyclops were collected at the end of the study, 120 d later. Community participation was solicited through a simple training program on copepod rescue before drum cleaning and facilitated by the addition of a drum marker to remind residents of copepod presence. Results showed good cooperation and after 4 mo all peridomestic drums, still supported variable numbers of cyclopoids. Average of larvae reduction was 37.5% for drums, 67.5% for flower vases, and 40.9% for tires. This study shows difficulties of using cyclopoids for tires and vases in areas where prolonged dry seasons desiccated these habitats and reduced copepod survival.

Aedes↗