UC Davis bacteriologist Paul Baumann and his colleagues are finding some answers to long-standing questions about the peculiar relationship between aphids and their internal companions, bacteria-like organisms known as "endosymbionts." The studies eventually may lead to better control of aphids, a major agricultural pest. Looking at the partnership from the endosymbionts' point of view, UC Davis postdoctoral researcher Chi-Yung Lai and Baumann recently revealed the molecular details of how endosymbionts produce excess tryptophan, an essential amino acid virtually absent in an aphid's sugar-rich diet of plant sap and long suspected to be key to the relationship. In other work, Baumann and University of Arizona entomologist Nancy Moran tracked the relationship back 200 million to 250 million years to an original infection of an aphid by bacteria. The genetic sequencing data not only traced the extended aphid and endosymbiont family trees back to the proverbial Eve, it established a direct means of calibrating an evolutionary molecular clock for the bacteria. New molecular techniques have contributed to a resurgence in symbiosis studies, Baumann says.