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At least 289 records · Page 16Linked to original sources
PubMed1999

Genetic mapping of resistance to Bacillus thuringiensis toxins in diamondback moth using biphasic linkage analysis.

Transgenic plants producing environmentally benign Bacillus thuringiensis (Bt) toxins are deployed increasingly for insect control, but their efficacy will be short-lived if pests adapt quickly. The diamondback moth (Plutella xylostella), a worldwide pest of vegetables, is the first insect to evolve resistance to Bt toxins in open-field populations. A recessive autosomal gene confers resistance to at least four Bt toxins and enables survival without adverse effects on transgenic plants. Allelic variants of this gene confer resistance in strains from Hawaii, Pennsylvania, and the Philippines. Here we exploited the biphasic nature of Lepidopteran genetic linkage to map this gene in diamondback moth with 207 amplified fragment length polymorphisms as DNA markers. We also cloned and sequenced an amplified fragment length polymorphism marker for the chromosome containing the Bt resistance gene. The results provide a powerful tool for facilitating progress in understanding, monitoring, and managing resistance to Bt.

Animals↗
PubMed1998

Insecticidal toxins from the bacterium Photorhabdus luminescens.

Transgenic plants expressing Bacillus thuringiensis (Bt) toxins are currently being deployed for insect control. In response to concerns about Bt resistance, we investigated a toxin secreted by a different bacterium Photorhabdus luminescens, which lives in the gut of entomophagous nematodes. In insects infected by the nematode, the bacteria are released into the insect hemocoel; the insect dies and the nematodes and bacteria replicate in the cadaver. The toxin consists of a series of four native complexes encoded by toxin complex loci tca, tcb, tcc, and tcd. Both tca and tcd encode complexes with high oral toxicity to Manduca sexta and therefore they represent potential alternatives to Bt for transgenic deployment.

Amino Acid Sequence↗
PubMed1992

Expression of the mosquitocidal toxins of Bacillus sphaericus and Bacillus thuringiensis subsp. israelensis by recombinant Caulobacter crescentus, a vehicle for biological control of aquatic insect larvae.

In the quest for effective control of mosquitoes, attention has turned increasingly to strains of the bacteria Bacillus sphaericus and Bacillus thuringiensis subsp. israelensis, which produce potent toxins with specific mosquitocidal activities. However, sedimentation of the bacterial spores limits the duration of effective control after field application of these bacilli. We describe here the cloning of genes encoding the 51.4- and 41.9-kDa toxins from B. sphaericus 2297, the 100-kDa toxin from B. sphaericus SSII-1, and the 130-kDa toxin from B. thuringiensis subsp. israelensis into the broad-host-range plasmid pRK248 and the transfer of these genes for expression in Caulobacter crescentus CB15. The recombinant C. crescentus cells were shown to be toxic to mosquito larvae. Caulobacter species are ubiquitous microorganisms residing in the upper regions of aquatic environments and therefore provide the potential for prolonged control by maintaining mosquitocidal toxins in larval feeding zones.

Animals↗
PubMed1985

[Physical preservation of food].

Physical preservation procedures are mostly aimed at prolonging the durability of foods by slowing down or repressing the spoilage mechanisms by the alteration of relevant parameters. Of these mechanisms of microbiological, enzymatic, chemical and mechanical type, especially the first-named are dealt with. Growth and multiplication of micro-organisms can be influenced by temperature, water activity and high-energy radiation. Depending on the susceptibility to deterioration of the products and the intensity of the processes based on these parameters, different degrees of durability are obtained. Micro-organisms are killed by the application of high temperatures in conjunction with the treatment times required in a given case. Relatively mild treatments affect only the vegetative forms (pasteurization), whereas more aggressive treatments are required to kill spores as well (sterilization). Recontamination of the products which were subjected to the two procedures must be avoided. Pasteurized foods require additional cold storage to prevent the spores from sprouting. Low temperatures reduce and repress the growth of micro-organisms (refrigeration) or prevent any activity of the micro-organisms (deep-freezing). The latter deprives the micro-organisms of the water they need for their growth. The same principle applies to another method of preservation where so much water is extracted from the product that the residual humidity no longer allows the micro-organisms to be active (drying). Ionising radiation can be used to reduce a potential risk to hygiene, to influence physiological processes, to control insects and to lengthen the durability of fresh food in the short term. Finally optimum product quality can be maintained by combining various procedures. If such methods cope with controlling the microbiological situation, attention must nevertheless be given to the other spoilage mechanisms as well, as they may prove to be limiting factors with respect to product quality.

Bacteria↗
PubMed2001

Entomopathogenic nematodes for the biocontrol of ticks.

Entomopathogenic steinemematid and heterorhabditid nematodes are increasingly used to control insect pests of economically important crops. Laboratory and field simulation trials show that ticks are also susceptible to these nematodes. The authors review the potential of entomogenous nematodes for the control of ticks.

Animals↗
PubMed1993

Vitelline membrane biogenesis in Drosophila requires the activity of the alpha-methyl dopa hypersensitive gene (I(2)amd) in both the germline and follicle cells.

The vitelline membrane of Drosophila eggs is composed of a family of proteins which are cross linked into an insoluble matrix with an overlying waxy layer that prevents desiccation. We present here three sets of experiments which show that integrity of the vitelline membrane requires the activity of the alpha methyl dopa hypersensitive (I(2)amdH or amd) gene in both egg chambers and follicle cells. We show that loss of amd activity either by dietary administration of inhibitors or in genetic mosaics of either the germ line or follicle cells leads to production of defective vitelline membranes and by in situ hybridization, that amd is expressed in both nurse cells and follicle cells. The amd gene product is the first non-structural protein gene described whose activity is required for vitelline membrane biosynthesis. Given its unique role in insects and its demonstrated sensitivity to dietary inhibitors, the amd gene product poses an attractive target for insect control.

Animals↗
PubMed1999

[The effect of infestation by mixed culture of Beauveria bassiana and Paecilomyces farinosus on reduction in numbers of experimental culture Blattella germanica L].

In this paper results of infestation of Blatella germanica L with mixed culture of insecticidal fungi belonging to one two species are presented. In the first stage of experiment the insects were infested first with B. bassiana spores and later with P. farinosus spores (strains L and P) was used as first and B. bassiana as second with time sequence of only 24 and 72 hours. Out of one species cultures tests were done alternately with strains L and P of P. farinosus. The control insects were always infested with fungi applied to cockroach in the first place. From comparison of data it results that irrespective of the time that elapsed from application of the first pathogen to the time of application of the second pathogen the number of dead individuals was always higher in experimental series than in control i.e. when only one pathogen was applied. After 30 days of experiment the highest mortality in females amounted to, 3.3% and in males--80.0% whereas in the control it amounted 6.6% and 20.0%. Respectively, after feeding on diet infested only with one pathogen. After 50 years the highest mortality amounted to 20% in females and 100% in males with control of 30% and 53.3% in meals and females, respectively. When the sequence of pathogen application was reversed, mortality after 30 day amounted to 53.3% in females and 36.7% in meals with corresponding numbers in controls beginning 26.6% and 26.6%, respectively. After elapse of 50 days the highest mortality in females was 90% and in males--100% with control showing mortality of 36.7% and 63.3% respectively. From comparison of numerical data complied in Table 1 it results that most advantageous time span between first and second infestation with fungi is 48 h. Mortality of cockroaches infested with fungi of two different species was higher than in insects infested with one species of fungi.

Animals↗
PubMed2000

Field tests on managing resistance to Bt-engineered plants.

Several important crops have been engineered to express toxins of Bacillus thuringiensis (Bt) for insect control. In 1999, US farmers planted nearly 8 million hectares (nearly 20 million acres) of transgenic Bt crops approved by the EPA. Bt-transgenic plants can greatly reduce the use of broader spectrum insecticides, but insect resistance may hinder this technology. Present resistance management strategies rely on a "refuge" composed of non-Bt plants to conserve susceptible alleles. We have used Bt-transgenic broccoli plants and the diamondback moth as a model system to examine resistance management strategies. The higher number of larvae on refuge plants in our field tests indicate that a "separate refuge" will be more effective at conserving susceptible larvae than a "mixed refuge" and would thereby reduce the number of homozygous resistant (RR) offspring. Our field tests also examined the strategy of spraying the refuge to prevent economic loss to the crop while maintaining susceptible alleles in the population. Results indicate that great care must be taken to ensure that refuges, particularly those sprayed with efficacious insecticides, produce adequate numbers of susceptible alleles. Each insect/Bt crop system may have unique management requirements because of the biology of the insect, but our studies validate the need for a refuge. As we learn more about how to refine our present resistance management strategies, it is important to also develop the next generation of technology and implementation strategies.

Animals↗