The extractive efficiency of kerosene on pyrethrum powders of varying degrees of fineness was tested by comparing the insecticidal efficiency of such extracts with standard extracts of pyrethrum containing 50, 75, and 100 per cent of the active constituents. House flies were used in the insecticidal tests and the time, in seconds, until 50 per cent of the flies were paralyzed was used as the main criterion for determining insecticidal power. Mortality data were taken but as reported in a previous paper, the percentage kill was not a sufficiently sensitive index to indicate small differences in the pyrethrin content of kerosene extracts. The efficiency of extraction on 12, to 15, 20, 30, and 45 mesh pyrethrum powders was about the same in each case: . it is estimated that 80 per cent extraction of the active constituents was obtained. Extraction of 200-mesh pyrethrum powder was more efficient, however, giving approximately 90 per cent of the active constituents. Apparently the achenes, or seeds, which contain a very large percentage of the active constituents, are not thoroughly crushed in powders varying from 12 to 45 mesh, whereas with 200-mesh powder the achenes are entirely broken up. This difference might account for the observed differences in the extractive efficiency of kerosene on these various grades of powder.
Document Type: Research Article
Publication date: February 1, 1933
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Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.