Systemic insecticides in livestock insect control.
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The effects of rose bengal, erythrosin B and fluorescein on ruminant digestion were evaluated by an in vitro rumen technique. Rose bengal reduced in vitro dry matter disappearance (IVDMD) values starting at .5 mM in the nutrient media and erythrosin B reduced IVDMD values starting at .05 mM in the nutrient media. Maximum reduction in IVDMD values was observed at 3.0 mM of rose bengal and erythrosin B. Fluorescein depressed digestion but not as severely as rose bengal or erythrosin B. Dry matter digestibility (DMD) values for steers given erythrosin B at a daily dosage of 6.5 mg/kg body weight were higher (P less than .05) than DMD values for control steers. DMD values were higher for steers given 16.3 or 26.1 mg erythrosin B/kg body weight daily than for the control steers, but the differences were not significant. There were no significant differences among animals given the different dosages in digestible energy. Recovery of erythrosin B from feces of treated steers varied with time, indicating that steers fed erythrosin B at a dosage of 6.5 mg/kg body weight might excrete feces during some periods of the day which would not control face fly development; however, administration of erythrosin B at a dosage of 16.3 mg/kg body weight would provide enough erythrosin B in feces to control face fly development throughout a 24-h period.
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Feeding tests showed that the powdered dried leaves and leaf extracts of L. bidwilli are toxic to the larvae of the housefly (Musca domestica), and the codling moth (Laspeyresia pomonella). The powdered material was not toxic to the light-brown apple moth (Epiphyas postvittana). The most active toxin is the lignan beta-peltatin-A methyl ether (II) and at a concentration of 100 ppm in a chemically defined diet it gave 98% mortality of housefly larvae.
During recent years many advances have been made in the development of insect control by genetic manipulation. These methods include the sterile-male technique, now well known, which depends on ionizing radiation or chemosterilization. The recent field experiment carried out by WHO in Rangoon, Burma, on Culex fatigans has demonstrated that naturally occurring cytogenetic mechanisms such as cytoplasmic incompatibility can be used successfully without the use of radiations or chemosterilants. The paper not only describes the experiment on Culex fatigans but also discusses basic concepts and theoretical considerations involved in genetic control of insects of public health importance. The possibility of using genetic mechanisms for the control of other vector species is also discussed. There are a number of problems which require study before genetic control can be used on an operational scale. These problems and suggestions for future research in this field are also outlined.
A genetic method for insect control was evaluated using the test organism, Drosophila melanogaster. The technique involved the displacement under a system of continuous reproduction, of standard strains by those carrying compound autosomes. The eradication of the replacements could subsequently be achieved through the use of temperature-sensitive lethal mutations.-While certain compound autosome strains failed to displace standards in population cages, even at the initial release ratio of 25:1, others were highly successful. Indeed, for some strains when the ratio of compounds to standards was as low as 9:1, the population rapidly went to fixation in favor of the compound line.-Hatchability was found to be an insufficient index of fitness to estimate the initial ratios of compounds to standards that would guarantee fixation of the former. Differences in other fitness components, such as development time, were detected that could seriously modify displacement, especially with continuous overlapping generations. The importance of examining the fitness of various compound lines and selecting the most competitive in cages, prior to field tests, cannot be overemphasized.
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