VCLH: Background and Biology
Erythroneura ziczac is found throughout the eastern and mid-west United States as well as Southern Canada (Varela et al. 2013). It has been documented as a pest of grape, apple, Boston ivy, and Virginia creeper vines (Wells and Cone 1989). In California, this pest was first reported in Butte County in 1984 and has subsequently been documented in Siskiyou, Shasta, Sutter and Trinity Counties. More recently there have been reports of E. ziczac in Solano, Sacramento, Yolo, Amador, and of course, Mendocino and Lake County.
Erythroneura ziczac is closely related to another common vineyard pest, the Western grape leafhopper (Erythroneura elegantula Osborn), which is regularly tolerated at low population densities in many vineyards. Both E. ziczac and E. elegantula overwinter as adults in leaf litter and debris or on shrubs and trees in and around the vineyard. As temperatures and photoperiod increase in the spring, the overwintering adults temporarily feed on a range of plants found around the vineyard such as dandelion and roses. As grapes begin to produce shoots and leaves, the E. ziczac move onto the vines and begin to feed and lay eggs in grape leaves, showing a preference for varietals with more glabrous leaves (i.e. Grenache, Chardonnay). As grapes lose their leaves at the end of the season, both E. ziczac and E. elegantula adults enter reproductive diapause and move to overwintering shelters where they reside until the following spring (Daane et al. 2013, Varela et al. 2013, Wells and Cone 1989, McKenzie and Bierne 1972, Fairbairn 1928).
Key Differences Between Virginia Creeper and Western Grape Leafhoppers
A key difference between these two leafhoppers is that E. ziczac oviposits earlier in the season, which leads to the earlier appearance of nymphs and next generation adults (Lowery and Judd 2007, Wells and Cone 1989). Additionally, E. ziczac reproduces later into the season than E. elegantula, which may allow E. ziczac to complete one additional generation per year than the E. elegantula. In a region like the North Coast, E. elegantula typically has 2-3 generations per year, whereas E. ziczac can have 2-4 generations per year. Finally, preliminary observations of E. ziczac indicate that this species may produce more eggs per adult than E. elegantula. Taken together, these traits can lead to earlier and more severe outbreaks of E. ziczac in vineyards.
The primary egg parasitoids of E. ziczac are Anagrus daanei and Anagrus tretiakovae [Hymenoptera: Mymaridae]. Erythroneura elegantula is also parasitized by A. daanei as well as by Anagrus erythroneurae. While A. daanei is commonly found in the North Coast, there are few records of A. tretiakovae in California, thus making A. daanei the key parasitoid of concern for E. ziczac control.
Importance of Overwintering Habitat for Parasitoids
Most important for parasitism of E. ziczac and E. elegantula is that these leafhopper species overwinter as adults near vineyards, whereas Anagrus wasps overwinter in the eggs of other leafhopper species. These alternate leafhopper hosts are typically found on non-crop vegetation in the natural habitats that surround vineyards (Doutt and Nakata 1965, Lowery et al. 2007). Our recent work in the North Coast has indicated that the primary overwintering habitat for A. daanei is wild blackberry (Rubus spp.), which can be found in abundance throughout this region. The proximity of a vineyard to suitable Anagrus overwintering habitat can significantly influence the timing and abundance of these parasitoids in a vineyard and this could in turn have implications for biological control of E. ziczac.
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