Constant Temperature Life Table Studies of Populations of Grape Phylloxera from Washington and Oregon, USA

Grape phylloxera is a recent pest threatening to destroy over 1100 ha of selfrooted winegrapes in the Pacific Northwest region of the USA. Some vineyards have coexisted with this pest for over 15 years while others have been devastated in less than 5 years. We conducted this study to determine if life processes of populations of phylloxera from four different areas in the Pacific Northwest, USA, would show differences in survival, development and reproduction when reared at myriad of constant temperatures (3 36oC at 3o intervals). Individual differences were observed among the four populations for development, survival and reproduction. Nevertheless, the numbers for each parameter followed a general trend among temperatures. The optimum temperature range for maximum response for all parameters was between 24oC and 27oC. Upper and lower temperature thresholds were, respectively, <6oC and >33oC. The results from this study and others support the hypothesis that localized differences in ‘virulence’ of infestations from vineyard to vineyard over an appellation may be a function, in part, of localized temperature differences caused by such factors as soil type, aspect, slope, pruning, ground cover, and plant spacing. INTRODUCTION Infestations of grape phylloxera (Daktulosphaira vitifoliae Fitch) have been rapidly expanding in the wine grape growing areas of Oregon, USA. Modern wine grape production started in the Pacific Northwest region of the USA in the early 1970’s. In 1990 the first infestations of radiciole grape phylloxera in wine grape, Vitis vinifera L., were found in both Oregon and Washington. Since that time more that 60 V. vinifera vineyards have been found infected in Oregon and only 8 vineyards have been found in Washington, most in juice grape, varieties of V. labrusca L. There have been no published studies on grape phylloxera in this region until recently (Connelly, 1995; Fisher and Hellman, 2000). Of the ~14,000 ha of wine grape planted in the Pacific Northwest, less than 16% are planted on phylloxera resistant rootstock. The entire wine grape crop in Washington is self-rooted. Producers have expressed a desire to have a base of knowledge on the biology of grape phylloxera from the region so that risk assessments could be made for replanting. They also expressed a need for the development of life tables in an attempt to estimate the risk factor for or against phylloxera spreading through Washington. Recently, Omer, et al. (1995, 1999) found that secondary organisms are, in part, responsible for vine decline. Fungi enter feeding wounds and slowly girdle the root. Phylloxera thrives when presented with certain conditions, i.e. food, moisture, temperature (Granett, et al., 1983; DeKlerk, 1974; Helm, et al., 1991). Most likely, as a phylloxera population increases there would be increases in the number of feeding wounds. This would result in an increase in damage. Granett and Timper (1987) found that the constant temperatures 21°, 24°, and 28°C were optimum for speed of development, survival, and reproduction of grape phylloxera whose origin was from central California. Downie, Fisher, and Granett (2001) found that populations from Oregon and Washington were more related to native phylloxera collected from V. riparia Michx. in the northern USA, while most California phylloxera were more related to Proc. on Phylloxera Infested Vineyards Eds: E.H. Rühl & J. Schmid Acta Hort 617, ISHS 2003 44 native phylloxera collected from V. vulpina L. located in the Atlantic Coast – Piedmont region of the USA. Additionally, V. vinifera affected by phylloxera in the Pacific Northwest, USA are located between 45°N latitude and 48°N latitude whereas the phylloxera used by Granett and Timper (1987) were from an area near 39°N latitude. With these differences and consideration of parthenogenic lines and the possibility for local adaptation, we wanted to know if there were differences among populations from Oregon and Washington phylloxera populations and if these populations would react similarly to constant temperatures as populations from California as documented by Granett and Timper (1987). MATERIALS AND METHODS The original eggs used in this study were obtained from colonies (4 –8 generations) of populations that had been collected from: 1) a vineyard in the Columbia Valley grape growing region of Washington, USA; 2) a vineyard in the northern area of the Willamette appellation in Oregon; 3) a vineyard in the central area of the Willamette appellation in Oregon; and 4) a vineyard in the southern area of the Willamette appellation in Oregon. The Willamette appellation covers an area N-S in western Oregon that is nearly 250 km long by ~ 100 km wide and is the most affected area with phylloxera in the Pacific Northwest region of the USA. After field collection, eggs were placed on excised Pinot noir roots in the laboratory and reared according to methods detailed by De Benedictis and Granett (1992) and Turley et al. (1996). The rearing temperature was 24°C with total darkness. Colonies were established from single founders (eggs from a single field collected adult that was feeding on a field collected root). The eggs were placed on phylloxera free newly excised roots and allowed to mature and develop a colony. Since the colonies we used originated from a single female and the eggs were produced by parthenogeny, we believe that all individuals from each colony were genetically identical. For experimentation newly laid eggs were taken from a particular colony and placed on an excised root. Ten eggs were placed on a single root that was in a petri dish. For each temperature and each origin, there were 10 to 15 replications (dependent on egg availability). A dish with one root and 10 eggs was considered a replication. All dishes for one temperature were placed in a constant temperature regime on the same day. Constant temperature regimes were produced in microprocessor controlled growth chambers (±0.5°C). There was a 24-hour, 7 day dark phase in all chambers. We used temperatures at 3°C intervals from 3°C to 36°C. Dishes were examined at different times according to temperature. At the low temperatures (#12°C), they were examined once per week until hatch. After hatch they were examined every other day. At all other temperatures dishes were examined every day. At each observation development was recorded. Eggs were determined to be dead when they turned brown to black. Nymphs and adults were determined to be dead when they turned brown to black and did not show any movement. Data was recorded for the following groups of stages: hatch – nymph 1, nymph 2 – nymph 3, nymph 4, adult (determined when first eggs produced). Survival for each stage was calculated as a proportion of the number of insects that had entered the previous stage. Survival from egg to adult was calculated for the number of adults as a proportion of the starting egg population. Here we report days to hatch and two measurements of days to reach adulthood. Days to hatch are the number of days from the initial exposure to a temperature regime to the time of mean hatch for each replication. Days to adult (from initial set-up) are the mean number of days it took to reach adulthood from the day that the dish with eggs was placed in the temperature regime. Whereas, days to adult are the mean number of days it took to reach adulthood from egg hatch. Gross fecundity is the number of eggs (mean) produced by an adult (all of the eggs produced by all of the adults in a dish / number of adults). Net fecundity (egg/♀/day) is the gross fecundity / the average days that a female was alive in a dish. Per capita growth rate is the number of eggs produced in a dish / the number of eggs initially placed in the experiment.