This study was designed to test the hypothesis that Dalbulus maidis (Hemiptera: Cicadellidae) serves as a natural source of mollicutes (Spiroplasma kunkelii and phytoplasma) that infect maize (Zea mays) following overseason in the State of Mato Grosso do Sul (MS), Brazil. The natural infectivity of D. maidis migrants was evaluated in spring plantings of 1997 and 1998 in the region of Anastácio (MS), where maize is not cultivated from April to September. Live leafhoppers were sampled in areas where: (A) maize was planted annually in the spring (October/December), and (B) maize had not been cultivated for several years. In a greenhouse, the leafhoppers were confined to healthy maize seedlings for pathogen inoculation. Two months later, the test plants were rated for diagnostic symptoms of S. kunkelii and tested by PCR for phytoplasma infection. Based on the transmission bioassays, S. kunkelii and phytoplasma were detected in 2 to 20% and 1 to 4% of the collected individuals, respectively. The appearance of infective adults soon after maize germination, even in the areas where maize had not been cultivated for several years, suggests that the mollicutes were transported in the overseason by migratory individuals of D. maidis.
