Research on the vine mealybug (VMB) and natural enemy populations was conducted in San Joaquin Valley (SJV), the Northern Interior Winegrape Region (Sacramento County), the North Coast (Sonoma/Napa Counties), and Central Coast (San Luis Obispo County) vineyards. Our goals are to determine the biological traits of VMB and its natural enemies that influence the success of biological controls, to promote resident natural enemy effectiveness by periodic release of parasitoids, and to import and release novel natural enemies.
Field studies show low levels of resident parasitoid activity in the Northern Interior, North Coast and Central Coast winegrape regions, as compared with the relatively high levels of parasitism in the SJV. Only Anagyrus pseudococci was recovered (Sacramento County). Low parasitism levels were a product of low VMB levels resulting from multiple insecticide applications. To improve resident parasitism, we released Anagyrus pseudococci, Leptomastix dactylopii and Leptomastidea abnormis in vineyards in the North Coast and Central Coast regions. L. dactylopii and L. abnormis were recovered, although at low levels. In augmentation trials, in which we released A. pseudococci, mealybug densities were lower in the release than control plots. Theseresults suggest that mass releases of A. pseudococci aided in economic control of VMB and could be a viable alternative to chemical control (pending cost evaluation).
As for novel natural enemies, we completed quarantine studies of a parasitoid (Coccidoxenoides peregrinus) imported from South Africa and, in 2005 began field releases in Central Coast vineyards. We conducted laboratory trials with VMB on grape and alternate host plant species. Here, we present results of VMB development on grapes. Temperature-related developmental studies were conducted at seven temperatures ranging from 12?34°C. The optimal, lower and higher threshold of fecundity were estimated at 22.6, 11.6 and 34.1°C, respectively The mealybug?s intrinsic rate of increase (how fast the population can grow) and the net reproduction rate (how many offspring it can produce) reached a maximum at 26°C and 433.4 degree days (a measurement of temperature development). The lower and upper threshold temperatures and optimum temperatures for development were estimated at 14.5, 35.4 and 22.2°C, respectively, and the thermal constant at 276.31 degree days.
What do all these developed temperature parameters mean for California and VMB control? These thresholds and constants were used in a degree-day model to estimate the number of generations that could develop in different grape growing regions of California and compared with development in the some of the world?s known infested regions. Four and six generations were estimated for the SJV and the North Coast region, respectively. There was also a higher reproductive rate in California as compared with studies in South Africa. Unfortunately, in comparison to other regions (e.g., Europe, South Africa), VMB is well adapted to both hot summer temperatures found in the both the SJV as well as cooler temperatures found in the coastal regions.