Abstract
The primary cause for the enormous increase of the beet leafhoppers during 1919. hinges on two factors: (1) there were no summer migrations of the pest during 1918, so that a large number of eggs were' deposited during the autumn; (2) the nymphs which hatched from these eggs found an abundance of green food not only in the cultivated areas but also on the plains and foothills after the heavy September rains germinated the seeds of the vegetation. The factors associated with the reduction in numbers of the beet leafhoppers vary in different years. The primary cause for the enormous reduction in numbers of the spring brood hoppers on the plains and foothills during 1923, was due to the early drying of the pasture vegetation during March instead of April and Mayas in previous years from 1919 to 1922. Secondary factors which reduce the number of leafhoppers in a natural breeding ground are natural enemies, spring and summer migrations, fungus diseases and rainfall.
Published Version
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