. Bulletin of the Department of Agriculture. Agriculture; Agriculture. 52 BULLETIN 276, U. S. DEPARTMENT OF AGRICULTURE. NATURAL CONTROL. It is doubtful if any species of plant louse is more harassed by enemies than is the pea aphis. According to the observations of other writers, which we are able to corroborate, the common aphis fungus, Empusa aphidis (fig. 13), is the most important natural check on the increase of Macrosiplium pisi. This fungus thrives under moist conditions, especially when accompanied by warmth, and hence it usually makes its appearance after a few days of rainy wea
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. 52 BULLETIN 276, U. S. DEPARTMENT OF AGRICULTURE. NATURAL CONTROL. It is doubtful if any species of plant louse is more harassed by enemies than is the pea aphis. According to the observations of other writers, which we are able to corroborate, the common aphis fungus, Empusa aphidis (fig. 13), is the most important natural check on the increase of Macrosiplium pisi. This fungus thrives under moist conditions, especially when accompanied by warmth, and hence it usually makes its appearance after a few days of rainy weather and more often in summer—that is, during the warmer months. As might be inferred, this fungus is conta- gious and spreads with wonder- ful rapidity, frequently, as ob- served by us, so completely eradicating the insects that it was difficult and sometimes im- possible to locate a single living plant louse. Diseased aphids first turn brownish and later become covered with the fungus threads. Thus weather conditions favorable for the growth of Empusa fungus are indirectly important. Furthermore, driving rains destroy great numbers of these plant lice, and very hot, dry weather seems to. Tig. 13. - Macrosiphum pisi attacked by a fungus. Enlarged. (Original.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original United States. Dept. of Agriculture. [Washington, D. C. ?] : The Dept. : Supt. of Docs. , G. P. O.
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