Investigation of the Grape Mealybug Complex and its Natural Enemies to improve biological control

Mealybug (grape, obscure, longtailed and vine mealybugs) pest densities and economic
damage has increased in many Central and North Coast vineyards. Our previous research
showed that Argentine ant populations increased mealybug pest problems and that, in the
absence of foraging ants, natural enemies can often control mealybug populations.
Unfortunately, most of the insecticides that effectively control ants are more toxic than
those used to control mealybugs. We have therefore investigated the use of less toxic ant
controls suitable for IPM systems. In 2003, we demonstrated that dilute concentrations of
insecticides delivered as liquid sucrose baits are a suitable alternative to broad-spectrum
sprays for Argentine ant control. In 2004, we worked towards development of a
commercial program, which we hope to have available in 2007. First, two commercially
available ant baits (imidacloprid in a sugar-water bait and spinosad in a granular protein
bait) were evaluated in field trials. We found a significant reduction in ant density and
mealybug damage with the imidacloprid treatment while the granular spinosad bait did
not impact ant populations. Second, we designed and tested bait stations that hold 10
times more bait than previous models, and can remain in the field up to 6 months without
maintenance (whereas previous models required cleaning and refilling every 2 to 3
weeks). A larger bait station will be essential for lower maintenance throughout the
season. In this first year?s study with these large stations, we did not find a significant
difference in ant densities between treatments. We believe that the high ant densities
encountered required more than one year of bait treatment or an initially higher density of
bait stations. Therefore, ant-bait stations will probably be used to maintain low
populations rather than reduce already existing and large ant populations. We also
investigated Argentine ant foraging distance and ant biology to better determine bait
station dispersion in the vineyard and timing during the season. Results show that most
bait movement is limited to the vines in the immediate vicinity of a bait station, although
Argentine ants showed the ability to carry bait over 200 feet from a bait station and
moved both down the vine row as well as across rows. Therefore, we can reduce the
number of stations per acre, which is also essential in developing an economical program.
Results from the ant biology study highlight the importance of maintaining stations in the
field in early spring and post-harvest. Ant foraging activity is greatest at the stations
during these times of year, coinciding with an increase in egg-laying in spring and
absence of a more attractive food source after the grapes are harvested. In 2005, we will
conclude many of these studies in order to produce guidelines on bait station design,
placement in the vineyard and seasonal timing.