The role of plant pathogens on the biology and ecology of vector and non-vector insect herbivores

A biotinylated DNA probe was used to detect the corn stunt spiroplasma in the non-vector planthopper, Peregrinus maidis. Pathogen detection is the first step in studying possible pathogen direct effects. I found no evidence for pathogen acquisition and multiplication in P. maidis, ruling out direct effects. The use of DNA probes revealed pathogen acquisition and multiplication by the vector insect, Dalbulus maidis.; To study indirect pathogen effects (i.e., due to changes in the plant mediated by the pathogen) I assessed changes in weight, fecundity, and longevity of P. maidis and D. maidis after feeding on CSS-infected plants. P. maidis feeding on diseased plants had a significantly lower weight than individuals on healthy plants. For D. maidis there was no significant treatment effect on weight. There were no significant differences in longevity or mean fecundity due to treatment for either insect. When weight was used as a covariate for mean total fecundity, treatments effects remained non-significant. However, using longevity as a covariate resulted in significantly higher fecundity for P. maidis on diseased plants, but no significant differences for D. maidis. There was a significant treatment by date interaction for P. maidis mean weekly fecundity. For D. maidis there was a significant date effect on mean weekly fecundity.; Significantly lower levels were found in diseased plants of glycine, ammonia, arginine, unknown amino acid #6, and a combination of four amino acids. Significantly higher levels of {dollar}alpha{dollar}-aminobutyric acid, methionine, {dollar}tau{dollar}-aminobutyric acid, tryptophan, ornithine, glucosamic acid, unknown amino acids #1 and #4, and the combination of three amino acids were found in diseased plants phloem. There was a significant date effect for phloem pH in diseased plants. There were no significant pH differences due to treatment.; Aster yellows MLO acquisition and multiplication was demonstrated in the non-vector Dalbulus maidis and in the vector Macrosteles fascifrons using a biotinylated DNA probe. Pathogen acquisition might be related to the "conditioning" phenomenon observed in D. maidis. Pathogen acquisition was also demonstrated using the polymerase chain reaction.