Tobacco thrips, Frankliniella fusca Hinds, are a major pest of many southeastern crops; however, very little information is available on the internal microflora of these insects. Pantoea ananatis (Serrano) Mergaert and Pantoea agglomerans (Beijerinck) Mergaert were each isolated from 9.6% of the 73 thrips tested from our laboratory colony. These bacteria were isolated from the same individual only once; in all remaing bacteria-infected thrips, only one bacterium was found. Tobacco thrips from our laboratory colony contained between 3.7 × 103 and 1.1 × 105 colony forming units (CFU)/ml/thrips of P. ananatis and between 1.2 × 103 and 2.5 × 105 CFU of P. agglomerans. Between 2.0 × 103 and 3.2 × 107 CFU of P. ananatis were isolated from leaflets exposed to thrips harboring P. ananatis. Leaflets on which thrips harboring P. agglomerans fed contained between 9.6 × 104 and 3.0 × 106 CFU of P. agglomerans. Field populations of tobacco thrips collected from onion plants harbored an average of 1.3 × 104 CFU/ml/thrips of P. ananatis, whereas those collected from peanut plants harbored an average 4.3 × 103 CFU of this bacterium. P. agglomerans was not isolated from field-collected thrips. Our data support a strong relationship between thrips feeding and the presence of these bacteria on the leaf surface. The fact that tobacco thrips are so strongly associated with P. ananatis, a known plant pathogen, is of particular importance. The leaf disk assay provided a consistently reliable method of detecting bacteria within the thrips body. Bacteria were not recovered from leaves unless the corresponding thrips also contained bacteria. This correlation suggests that this assay can be used to detect P. ananatis and P. agglomerans within the body of an individual thrips without homogenizing and plating the individual insect.
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Vol. 95 • No. 6