ELISA versus immunolocalization to determine the association of Erwinia tracheiphila in Acalymma vittatum (Coleoptera : Chrysomelidae)

DAS-ELISA, immunohistochemistry and electron microscopy were used to invest igate the association of the causal agent of bacterial wilt, Erwinia trache iphila (Smith), within the beetle Acalymma vittatum (F.). After a 24-h acqu isition period, a high percentage of individuals tested positive for E. tra cheiphila antigen using both immunohistochemistry (100%) and DAS-ELISA (70- 60%). Both assays showed that the antigen remained in beetles long after th e initial acquisition, with the percentage declining during incubation. Usi ng ELISA, the percentage decreased to 4.7% within 3 d after acquistion, the n increased to 10% within 10 d and remained at 10% for 30 d. Immunoperoxida se assays of paraffin embedded gut sections were more sensitive, and showed that 95% of the beetles harbored the pathogen after 10 d and 20% after 30 d. E. tracheiphila antigen was present throughout the digestive tract soon after acquisition, but only small clusters of E. tracheiphila were otserved along the alimentary canal 3 d after transfer onto clean plants. After 10 and 30 d on clean plants, E. tracheiphila antigen reaction was stronger and clusters of bacteria were more numerous. primarily in the posterior midgut and anterior portion of the hindgut. Scanning electron microscopy and TEM photomicrographs confirmed the presence of bacterial cells resembling E. tr acheiphila associated with the intima of the hindgut 1 and 30 d after acqui sition. This demonstrated the sensitivity of immunohistochemistry for detec ting E. tracheiphila within its vector, and suggests a long-term extracellu lar endosymbiotic association of E. tracheiphila with the alimentary canal of A. vittatum.