Abstract: Xylella fastidiosa colonizes the xylem network of host plant species as well as the foregut of required insect vectors to ensure its efficient propagation. Disease management strategies remain inefficient due to a limited comprehension of mechanisms governing both insect and plant colonization. It was previously shown that X. fastidiosa has a functional chitinase (ChiA), and that chitin likely serves as a carbon source for this bacterium. We expand on that research showing that a chiA mutant strain is unable to grow on chitin as the sole carbon source. qPCR assays allowed us to detect bacterial cells on the foregut of vectors after pathogen acquisition; populations of the wild type and complemented mutant strain were both significantly larger than the chiA mutant strain 10 days but not 3 days post acquisition. These results indicate that adhesion of the chiA mutant strain to vectors may not be impaired, but cell multiplication is limited. The mutant was also affected in its transmission by vectors to plants. In addition, the chiA mutant strain was unable to colonize host plants, suggesting that the enzyme has other substrates associated with plant colonization. Lastly, ChiA requires other X. fastidiosa protein(s) for its in vitro chitinolytic activity. The observation that the chiA mutant strain is not able to colonize plants warrants future attention to the substrates for this enzyme.