Project Title: Quantifying Grape Mealybug’s Efficiency as a Vector of Grapevine Leaf Roll Associated Viruses (GVLRAVS)
Project Duration: 2016-2019 (3 years)
Principal Investigator(s): Doug Walsh
Organization: WSU IAREC Entomology
Address: 24106 North Bunn Rd, Prosser, WA 99350
Telephone: 509-786-9287
Email: dwalsh@wsu.edu
CO-PI(s): Naidu Rayapati
Organization: WSU IAREC Plant Pathology
Address: 24106 North Bunn Rd, Prosser, WA 99350
Telephone: 509-786-9215
Email: naidu.rayapati@wsu.edu
CO-PI(s): Jonathan O’Hearn
Organization: WSU Entomology
Address: 24106 North Bunn Rd, Prosser, WA 99350
Telephone: 509-786-9244
Email: jonathan.ohearn@wsu.edu
Project Summary:
Grape mealybugs (Pseudococcus maritimus) have been identified as the primary vector of grapevine leafroll associated viruses (GLRaVs) in Washington vineyards. While it is known that the grape mealybug is the vector of GLRaVs their efficiency as a vector had not been determined. Is feeding by a single infected mealybug crawler enough to vector the virus? Or does it take some cohort of mealybug crawlers feeding to transmit the virus? Current mealybug control measures use systemic insecticides that require some period of feeding before the insecticide will inhibit the mealybugs from feeding or cause mortality. It is unknown if the time lag between the initiation of feeding by mealybugs and the cessation of feeding by the mealybug crawlers as a result of exposure to systemic insecticides would allow for the transfer of the viruses. Knowing the grape mealybug’s vector efficiency and the effectiveness of current chemical controls should help growers build better future Integrated Pest Management (IPM) programs to control the spread of GLRaVs.
To determine if a low cohort of mealybugs were capable of transferring the virus, GVLRaV infected mealybugs were placed on clean potted grapevines. On 20 potted grapevines per treatment, 1 and 5 infected mealybug crawlers were placed on each grapevine and allowed feed and persist for as long as they could. The potted grapevines were allowed to sit for one year for the titer of virus to build in the vines. The vines were then tested using PCR analysis to determine the percentage of grapevines that became infected. To test the current systemic insecticides effectiveness in preventing the spread of the virus 40 potted grapevines per insecticidal treatment were treated with the insecticides imidacloprid, spirotetramat (Movento™), and flupyridifuron (Sivanto™). In each insecticidal treatment, 20 grapevines were treated with the high field rate and the other 20 with the low field rate. On each grapevine 10 GVLRaV infected crawlers were transferred from infected grapevines, and allowed feed and persist for as long as they could. The grapevines were then allowed to sit for one year to allow for the titer of virus to build in the vines, which will be July 2019. PCR analysis will be used to determine the percentage of grapevines that became infected as compared to control plants not treated with insecticide.
Our ultimate goal of these experiments was to increase our knowledge of the epidemiology of GLRaVs and its grape mealybug vector to help growers improve their future IPM programs. Our first experiment allowed us to produce the number of mealybugs required to achieve this. Our second experiment’s goal was to determine the number of mealybugs required to transfer the virus. And our last goal was to determine if current management practices are effective in slowing the spread of GLRaVs in vineyards and possibly reduce unnecessary insecticide applications.
Read more by downloading the full report above.