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At least 523 records · Page 29Linked to original sources
PubMed2006

Anthelmintic resistance and alternative control methods.

Anthelmintic resistance has been a problem almost from the first use of the drugs introduced during the past 50 years. Evaluation of anthelmintics on a specific farm is essential to determine which drugs may be used in controlling parasite numbers. Treatment of livestock during the season in which parasite transmission is unfavorable lessens pasture contamination. Targeting treatment places less pressure on susceptible worms, diluting the resistant parasite population. Pasture management and using safe pastures for animals at highest risk lower pasture exposure. Selection for individual animals resistant to the effects of parasites lessens the need for use of anthelmintics. Alternatives to anthelmintics include cryptic antigen vaccines, copper wires, and biologic compounds.

Animals↗
PubMed1973

Prospects of chemosterilant and genetic control of rodents.

This paper discusses some requirements of an ideal rodent chemosterilant, analyses the advantages of chemosterilants over other control methods, and compares the potential values of chemosterilants that affect females, males, and both sexes. Examples are given of specific situations where chemosterilants will be valuable in rodent control, together with suggested methods of applying them. The theory and practicability of using genetics in rodent control are also discussed. Neither the chemosterilant nor the genetic method is expected to become a panacea, but their eventual application will be a significant advance in rodent-control technology. Since both approaches are based on sound biological principles and are relatively safe, they should be helpful in regulating rodent populations in the future.

Animals↗
PubMed2004

Understanding and improving transgene stability and expression in insects for SIT and conditional lethal release programs.

Genetically transformed insect pests provide significant opportunities to create strains for improved sterile insect technique and new strategies based on conditional lethality. A major concern for programs that rely on the release of transgenic insects is the stability of the transgene, and maintenance of consistent expression of genes of interest within the transgene. Transgene instability would influence the integrity of the transformant strain upon which the effectiveness of the biological control program depends. Loss or intra-genomic transgene movement would result in strain attributes important to the program being lost or diminished, and the mass-release of such insects could significantly exacerbate the insect pest problem. Instability resulting in intra-genomic movement may also be a prelude to inter-genomic transgene movement between species resulting in ecological risks. This is less of a concern for short-term releases, where transgenic insects are not expected to survive in the environment beyond two or three generations. Transgene movement may occur, however, into infectious agents during mass-rearing, and the potential for movement after release is a possibility for programs using many millions of insects. The primary methods of addressing potential transgene instability relate to an understanding of the vector system used for gene transfer, the potential for its mobilization by the same or a related vector system, and methods required to identify transformants and determine if unexpected transgene movement has occurred. Methods also exist for preventing transposon-mediated mobilization, by deleting or rearranging vector sequences required for transposition using recombination systems. Stability of transgene expression is also a critical concern, especially in terms of potential epigenetic interactions with host genomes resulting in gene silencing that have been observed in plants and fungi, and it must be determined if this or related phenomena can occur in insects.

Animals↗
PubMed2002

The evolution of sex determination systems in dipteran insects other than Drosophila.

The multitude of sex determination mechanisms displayed in dipteran insects has usually been described in terms of variations on a single principle in which the primary signal of the primitive pathway consists of a single allelic difference at one locus. Evolution of sex determination mechanisms is thought to have occurred by the addition of genes below the top gene of the pathway. The elucidation of the complex sex determination pathway of Drosophila melanogaster, as well as recent evidence that the basal genes of the pathway seem to be conserved across metazoan genera both in structure and, to a lesser degree, in function, points towards the possibility that sex determination pathways may have evolved from the bottom-up. Further to this is the question of whether the dominant male-determining factor, M, which is found in a number of insect species, represents part of the ancient sex determination pathway or is a later addition to the pathway. This, together with the possibility that the M factors found in numerous dipteran insect species may have a common origin, is discussed. The similarities of the sex determination pathways under the control of M and the implications in relation to the construction of genetic sexing strains for biological control are also discussed.

Animals↗
PubMed2003

Evaluation of transgenic Bt corn for resistance to the Asian corn borer (Lepidoptera: Pyralidae).

The Asian corn borer, Ostrinia furnacalis (Guenée), is the most important insect pest on corn in China. Bt transgenic corn provides a new tool for Asian corn borer control. Monsanto's YieldGard Bt transgenic corn expressing Cry1Ab protein, and a non-Bt control, were evaluated in Beijing. Laboratory bioassays were carried out by exposing neonates to an agar-free diet containing Bt corn whorl leaves, tassels, and anthers, or by exposing neonates directly to fresh silk and pollen. These are the tissues initially attacked by neonates in the field. All of these tissues, with the exception of pollen, contained sufficient insecticidal protein to kill > or = 95% of larvae within 7 d. Surviving larvae had also not grown beyond first instar and weighed < or = 0.1 mg. Although larvae feeding on Bt corn pollen were significantly smaller than those on non-Bt corn pollen, there was no significant difference in mortality. Field trials were also conducted with artificial infestations of Asian corn borer at mid whorl, late whorl, and silking stages. Damage ratings and number of larvae surviving per plant indicated that Bt corn was highly resistant to Asian corn borer. Therefore, YieldGard offers the potential for season-long protection against first- and second-generation Asian corn borer.

Animals↗
PubMed1992

Reduction of mortality rates of Bacillus thuringiensis var. israelensis aqueous suspensions due to freezing and thawing.

When studying the behavior (carry, dispersion, persistence) of Bacillus thuringiensis var. israelensis (B.t.i.) formulations used in the treatment of rivers or streams for black fly control, a large number of samples containing small quantities of B.t.i. are required for proper analysis. Freezing is a useful procedure to prevent enzymatic alteration or bacterial growth in samples before bioassays are to be performed. Using Aedes atropalpus neonate larvae, we studied the effect of freezing and thawing of B.t.i. aqueous suspensions by looking at mortality response parameters such as the slope and the LC50 of the probit regression. Initial concentration values of 1, 5, 10 and 20 mg/liter at the moment of freezing of the B.t.i. suspensions did not significantly affect toxicity. The number of freeze-thaw cycles greatly increased the LC50 values without much change to the slope of the log-probit regressions. We derived an equation that allowed us to compensate for the loss of toxicity of a given B.t.i. sample, knowing the number of freeze-thaw cycles.

Aedes↗
PubMed2000

Trials to control South American ticks with entomopathogenic fungi.

Ticks are parasites of great importance to man, domestic, and wild animals. In spite of the progress of the science, thus far, ticks are controlled mainly by chemical acaricides and when this technique is used in an indiscriminate way it can lead to ambiental pollution and development of tick resistance to acarcides. The studies developed in the Universidade Federal Rural do Rio de Janeiro demonstrate that some isolates of the fungi Metarhizium anisopliae and Beauveria bassiana are pathogens for ticks and their action effects the mortality of ticks and reduces the populational levels in subsequent generations. In future, research needs to address the search of new pathogens; the association of biological with chemical products seeking an synergistic action; the search of formulations that propitiate increased stability, and careful studies on the safety of biological products for use in animals.

Animals↗
PubMed1993

Protection from ultraviolet irradiation by melanin of mosquitocidal activity of Bacillus thuringiensis var. israelensis.

A process for production, isolation, and purification of melanin produced by the fermentation of Streptomyces lividans 66 harboring a recombinant plasmid pIJ702-bearing tyrosinase gene has been developed. The efficacy of melanin in the protection of mosquito larvacidal activity of Bacillus thuringiensis var. israelensis against uv light has been studied. Results obtained by the live cell counts and the bioassay of residual mosquitocidal activity of B. thuringiensis var. israelensis after exposure to uv radiation showed that melanin is an excellent photoprotective agent.

Aedes↗
PubMed2002

Roles of Bacillus endospores in the environment.

The occurrence and diverse roles of Bacillus spp. and their endospores in the environment is reviewed, with particular emphasis on soil ecology, host-symbiont and host-parasite interactions, and human exploitation of spores as biological control agents and probiotics.

Animals↗
PubMed1999

Biological control of helminths.

As a potential component in future integrated parasite-control strategies, biological control by means of predacious fungi seems to be moving from a promising possibility toward becoming a reality, and the netforming nematode-destroying fungus Duddingtonia flagrans appears to be the candidate of choice. Not only has this fungus been found in, and isolated from, fresh sheep, cattle and horse faeces, but it also appears to be the only fungus that is able to consistently and significantly reduce the number of infective trichostrongyle larvae in faeces from animals fed fungal spores. Results from the last few years have shown that D. flagrans is able to trap and destroy free-living stages of the most important and common trichostrongylid larvae with very similar external life-cycles, as well as larvae of parasites with a slightly different transmission biology (Nematodirus spp., Dictyocaulus viviparus). The introduction of microfungi for biological control could be as part of a feed supplement or incorporated in feed-blocks presented to animals which are raised under relatively intensive conditions and constant surveillance. Apart from the special niche for organic farmers, such a product would be suited for horses, small ruminants (as either milking herds or housed daily for other reasons), cattle in special situations and free-roaming pigs. The most important constraint, still, for a major breakthrough in biological control in the latter is the lack of good antagonists against the long-lived and rather resistant infective stages of parasites, being transmitted as larvae inside the egg. Since the first Conference on Novel Approaches to the Control of Helminth Parasites of Livestock in Armidale, Australia, 1995, there has been a steady evolution within the area of biological control of parasitic nematodes. Today this principle is being exploited and tested out in almost all parts of the world, under various climatic conditions and production systems. Where, in the past, a large part of the work focused on cattle and to a lesser degree horse and sheep parasites, the focus of the research in many of the newly involved countries is on small ruminants, because of their importance to primarily small-scale farmers in local communities. Today research and trials are either on-going or being planned in many developing countries, as well as in countries in transition. The involvement of multinational agencies in addition to national and industrial interests is very welcome and should increase the chances and keep up the momentum for development and implementation of biological control in future animal production around the world.

Animals↗
PubMed2003

Degradation of the Cry1Ab protein within transgenic Bacillus thuringiensis corn tissue in the field.

Large quantities of Bacillus thuringiensis (Bt) corn plant residue are left in the field after harvest, which may have implications for the soil ecosystem. Potential impacts on soil organisms will also depend on the persistence of the Bt toxin in plant residues. Therefore, it is important to know how long the toxin persists in plant residues. In two field studies in the temperate corn-growing region of Switzerland we investigated degradation of the Cry1Ab toxin in transgenic Bt corn leaves during autumn, winter and spring using an enzyme-linked immunosorbent assay (ELISA). In the first field trial, representing a tillage system, no degradation of the Cry1Ab toxin was observed during the first month. During the second month, Cry1Ab toxin concentrations decreased to approximately 20% of their initial values. During winter, there was no further degradation. When temperatures again increased in spring, the toxin continued to degrade slowly, but could still be detected in June. In the second field trial, representing a no-tillage system, Cry1Ab toxin concentrations decreased without initial delay as for soil-incorporated Bt plants, to 38% of the initial concentration during the first 40 days. They then continued to decrease until the end of the trial after 200 days in June, when 0.3% of the initial amount of Cry1Ab toxin was detected. Our results suggest that extended pre- and post-commercial monitoring are necessary to assess the long-term impact of Bt toxin in transgenic plant residues on soil organisms.

Animals↗