Survival ofVerticillium albo-atrumfrom Alfalfa in Feces of Leaf-Chewing Insects

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Abstract
Alfalfa leaves infected with V. albo-atrum were fed to leaf-chewing insects, grasshoppers (Melanoplus sanguinipes and M. bivittatus), alfalfa weevil (Hypera positica), and woolly bear (Apantesis blakei), to determine survival of the pathogen after passage through their digestive tracts. V. albo-atrum survived in the digestive tracts of all tested species, usually first appearing in the feces 1 day after feeding. The percentage of feces contaminated by V. albo-atrum varied among individuals within species and was related to the duration of feeding on diseased tissues. The average percentage of contaminated feces in adult M. sanguinipes was less than 14% after 1 day of feeding the insects with diseased tissue but increased to 49% after 3 days of feeding. V. albo-atrum was eliminated from the digestive tracts of grasshoppers by changing the diet to uninfected alfalfa leaves. The time required for complete removal of the pathogen appeared to be related to the level of contamination in digestive tracts, averaging 1.6 days for individuals with less than 25% of pathogen-contaminated feces and 6.1 days for those with more than 75% of contaminated feces in their digestive tracts. When grasshopper feces contaminated with V. albo-atrium were buried near roots of alfalfa seedlings, 20.8 and 13% of plants became 1 and 2, respectively. The role of leaf-chewing insects in the dissemination of V. albo-atrum in alfalfa and other crops is discussed.