Submitted to: Annals of the Entomological Society of America
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/16/2011
Publication Date: 3/24/2012
Citation: Krugner, R., Sisterson, M.S., Lin, H. 2012. Effects of Insect Origin, Gender, and Age on Transmission of Xylella fastidiosa to Grapevines by Homalodisca vitripennis (Hemiptera: Cicadellidae). Annals of the Entomological Society of America. 105(2):280-286. Interpretive Summary: Pierce’s disease (PD) is an important grapevine abnormality caused by the bacterium Xylella fastidiosa. In California, the bacterium is transmitted by several leafhopper species including the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis. While transmission efficiency is known to vary among vector species, less is known about the degree to which transmission efficiency varies among populations of the same species or between genders of the same species. As there is some evidence of differentiation between GWSS populations in California, a study was initiated to determine if transmission of X. fastidiosa to grapevines is affected by insect population origin, gender, or age. To test the effects of those GWSS characteristics on transmission, insects were given a 96-h acquisition access period on infected grapevines and a 72-h inoculation access period on healthy grapevines. At the conclusion of the test, ~30% of test plants were infected, with no effect of GWSS origin, gender, or age on transmission, confirming that these factors do not affect transmission. Therefore, understanding the underlying mechanism of individual-specific movement and dispersal behaviors of GWSS can help reveal the possible ecological complexities associated with pathogen spread and further explore more effective approaches for controlling GWSS and Pierce’s disease.
Technical Abstract: Homalodisca vitripennis (Germar) is an invasive insect vector in California, where it transmits the bacterium Xylella fastidiosa to grapevines and other crops. Transmission efficiency of X. fastidiosa to grapevines by male and female H. vitripennis originating from two geographically separated populations in California (Riverside and Bakersfield ) was evaluated. To test effects of insect origin, gender, age, and vector load on transmission, insects were given a 96-h acquisition access period on infected grapevines and caged in groups of 5 on healthy grapevines for a 72-h inoculation access period. At conclusion of tests, polymerase chain reaction (PCR) and Real-time PCR determined that each grapevine received a mean (± SD) of 0.8 ± 0.9 X. fastidiosa positive insects and that 29% of test plants were infected, with no effect of vector origin, gender, or age on pathogen acquisition or inoculation. However, test date significantly affected the number of X. fastidiosa positive insects per test plant. A mean (± SD) of 3.12 ± 6.86 x 106 bacterial cells/ 20 ng of total DNA was detected in infected grapevines. Increasing the number of H. vitripennis carrying X. fastidiosa per test plant significantly increased transmission but did not affect the number of bacterial cells detected in infected plants 12 weeks post inoculation. Confirmation that insect origin, gender, and age do not affect transmission efficiency of X. fastidiosa under controlled laboratory conditions indicates that rates of pathogen spread in the field are determined by local ecological aspects affecting vector population density and gender- and/or age-specific movement patterns.