Vector ecology informs epidemiology: implications of glassy-winged sharpshooter oviposition behavior and nymphal dispersal from oviposition sites on epidemiology of <i>Xylella fastidiosa</i>

For an insect transmitted pathogen to spread, an insect must feed on an infected plant to acquire the pathogen and subsequently disperse and feed on a healthy plant. Because juvenile insects are wingless and adults are typically winged, adult insects are assumed to disperse greater distances and, therefore, have a greater contribution to pathogen spread. The glassy-winged sharpshooter (Homalodisca vitripennis) transmits Xylella fastidiosa, a bacterial plant pathogen that causes several plant diseases including Pierce's disease of grapevines. For many insects, oviposition preference is directly related to offspring performance on that host. However, studies have documented that glassy-winged sharpshooter ovipositional preference is not linked to offspring performance. One hypothesis for the lack of an association between oviposition preference and offspring performance by the glassy-winged sharpshooter is that nymphs disperse from oviposition sites shortly after egg hatch. Because glassy-winged sharpshooter nymphs are capable of transmitting X. fastidiosa, routine nymphal dispersal could contribute to secondary (plant-to-plant) pathogen spread. Dispersal of glassy-winged sharpshooter nymphs from oviposition sites on preferred and unpreferred hosts was quantified vertically and horizontally. In vertical movement tests, majority of nymphs moved upward into the grapevine canopy shortly after egg hatch, with faster dispersal away from less preferred plants. In horizontal movement tests, hourly dispersal rates were greater on the less preferred host than on the preferred host, with nymphs dispersing from unpreferred plants and congregating on preferred plants. Results indicate that glassy-winged sharpshooter nymphs routinely disperse from oviposition sites shortly after egg hatch in search of higher quality hosts. Such routine nymphal dispersal may contribute to secondary (plant-to-plant) pathogen spread in managed and natural systems.