Apple trees were grown in nutrient culture in the greenhouse on varying levels of nitrogen and phosphorus supply during two seasons. Females of Panonychus ulmi Koch and Tetranychus telarius (L.) were cultured on leaves detached from the trees and the resulting progeny were counted. Analyses of foliage were made for total nitrogen, phosphorus and potassium. Analyses of variance were performed on the results of the foliage analyses and mite counts, arid tests for correlation coefficient r were made on absorbed elements with populations. Increasing nitrogen from 20 to 200 p.p.m. effected significant increases in both mite species. Increasing nitrogen to 800 p.p.m. elicited a further increase from T. telarius during one season. Both species were positively related with absorbed nitrogen, but only T. telarius was significantly correlated. Previously the author found a negative correlation in tomato foliage at levels of absorption about twice that of the apple trees herein reported, when nitrogen supply was increased, although doubling all the elements in the standard solution resulted in doubled mite populations. Absorbed nitrogen in apple foliage was negatively correlated with T. telarius population when phosphorus supply was increased. It was found that in apple foliage, unlike tomato foliage, nitrogen and phosphorus evidenced antagonism, particularly when nitrogen supply was increased. A tendency appeared for absorbed phosphorus to be positively correlated with T. telarius below 0.20% phosphorus and negatively correlated when percentages somewhat higher were reached in the foliage. It may be concluded that interrelations among the ions and different ranges of absorption can account for seemingly contradictory effects on mite populations. Individual variability in mite reproduction rates has made it necessary to deal with large populations in order to draw firm conclusions, and wide percentage differences in populations are required in order to result in significant differences. In this respect T. telarius has proved to react with more sensitivity and less variability than P. ulmi to changes in element supply and absorption. The tests showed that T. telarius populations develop more rapidly than P. ulmi given the same conditions. T. telarius appears to react favorably to wider ranges of nitrogen absorption and it follows that it would be capable of doing further damage to foliage after some bronzing by P. ulmi has occurred.
Document Type: Research Article
Publication date: June 1, 1958
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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.