The Ability of the Beet Leafhopper to Regain Lost Vitality When Transferred From Unfavorable to Favorable Host Plants

Abstract

In a previous paper (Cook '44) the writer described a longevity test, in which female beet leafhoppers in lots of about 100 were caged at a constant temperature of 20? + 0.50? C. and supplied with water, but no food. The average length of life, determined by daily observations, was used to measure the vitality of the insects. The fat content of the insects, determined by extraction with ethyl ether or chloroform, was shown to be highly correlated with longevity, and was also used as a measure of the vitality of the leafhoppers. It was shown that the female leafhoppers possessed a very high vitality when they left their summer host plants in the fall, and that when they were confined on sugar beets this vitality declined gradually during the fall and early winter, reaching a low, but nearly constant value during January. This low vitality was maintained the rest of their lives, or until the eggs were laid, in February and March. The leafhoppers lost their vitality more rapidly when confined on desert sage (Atriplex polycarpa (Torr.) S. Wats.) than when confined on sugar beets. Leafhoppers confined on desert sage consistently continued to lose vitality, without ever establishing an equilibrium, and finally (lied before any eggs were laid. Desert sage is one of the most abundant shrubs in the areas where the leafhoppers spend the fall and winter, and a large part of the leafhopper population is forced to feed on this plant for a period ranging from 1 to 3 months in different years. This makes it highly desirable to determine whether leafhoppers that have fed on desert sage until their vitality is at a low ebb can regain their lost vitality when placed upon a more favorable host plant. In order to obtain information on this point, experiments were conducted at Modesto, Calif., during the fall and winter seasons of 1937-38 to 1940-41, inclusive, the results of which are reported here.