Studies On The Biology Of The Variegated Grape Leafhopper Erythroneura Variabilis Beamer

Author : Sam Houston Wilson
Publisher :
ISBN 13 :
Total Pages : 123 pages
Book Rating : 4.:/5 (957 download)

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Download or read book Influence of Landscape Diversity and Flowering Cover Crops on Biological Control of the Western Grape Leafhopper (Erythroneura Elegantula Osborn) in North Coast Vineyards written by Sam Houston Wilson and published by . This book was released on 2014 with total page 123 pages. Available in PDF, EPUB and Kindle. Book excerpt: Modern agriculture is characterized by specialized production and the use of monoculture cropping practices. These agroecosystems are at once concentrating habitat for crop pests and eliminating habitat for natural enemies. Multiple studies have demonstrated that such changes can lead to a decrease or total loss of biological control of pests. At the same time, expansion of monoculture cropping systems across entire agricultural regions has led to the creation of landscapes that are entirely dominated by a small number of crops and devoid of natural habitats. In the same way, entire regions can experience a reduction or loss of biological control to agriculture. As such, a number of studies have compared crop fields with high and low habitat diversity and found that diversified cropping systems tend to have enhance natural enemy populations and increased biological control of pests. At the same time, another set of studies have demonstrated that monoculture cropping systems can still experience high levels of biological control so long as they are situated in a landscape with high levels of habitat diversity surrounding them. More recently, it has been proposed that the use of on-farm habitat diversification to enhance biological control will likely be influenced by the area and quality of natural habitat surrounding the farm (i.e. landscape diversity). This dissertation was designed to evaluate the influence of habitat diversity at the local and landscape scale on biological control of the Western grape leafhopper (Erythroneura elegantula Osborn; Hemiptera: Cicadellidae) in North Coast wine grape vineyards. The key parasitoids of E. elegantula are Anagrus eryhthroneurae S. Trjapitzin & Chiappini and A. daanei Triapitsyn (Hymenoptera: Mymaridae). These Anagrus parasitoids are intimately tied to the natural habitats that surround vineyards due to the fact that in order for them to successfully overwinter they must parasitize an alternate leafhopper host that overwinters in an egg stage (E. elegantula overwinters in the vineyard as an adult). These alternate leafhopper hosts are known to reside in the natural and semi-natural habitats that surround North Coast vineyards. As such, it is thought that biological control of E. elegantula in vineyards is particularly sensitive to changes in landscape diversity. At the same time, the use of monoculture cropping practices results in a vineyard environment that is very inhospitable to natural enemies of E. elegantula, including Anagrus spp. Previous studies have demonstrated that without floral nectar (or an analogous solution) the lifespan of Anagrus parasitoids can be less than two days and it may be that the introduction of flowering cover crops into vineyards could possibly increase biological control of E. elegantula by enhancing Anagrus longevity in the field. In this way, increased habitat diversity at both the field and landscape scale may support increased natural enemy populations which would lead to increased biological control of E. elegantula. For this dissertation, a series of studies were conducted in order to evaluate how changes in habitat diversity at the field and landscape scale could affect natural enemy populations and ultimately influence biological control of E. elegantula. First, overwintering habitat of Anagrus spp. was evaluated to identify the specific host plant species that contained leafhopper eggs that these parasitoids were attacking in natural habitats during the winter, as well as throughout the rest of the year. Second, vineyards that were adjacent to riparian habitat were studied in order to evaluate how distance away from a large natural habitat patch influenced the timing, density and impact of natural enemies in the vineyard. Third, in order to isolate the influence of landscape diversity, a multi-year study was conducted to monitor biological control of E. elegantula in a number of vineyard monocultures that were situated in low, intermediate and high diversity landscapes. Finally, over the course of several years the use of flowering summer cover crops was developed in collaboration with commercial wine grape growers and vineyard trials were subsequently conducted to evaluate the ability of these flowering cover crops to enhance biological control of E. elegantula. In order to evaluate how changes in the landscape influenced the effectiveness of this on-farm habitat diversification practice, these cover crop studies were conducted at multiple vineyards that were situated in low, intermediate and high diversity landscapes. Results from these studies indicate that the area and composition of natural habitats surrounding vineyards can have a significant influence on biological control of E. elegantula. Reduced pest populations in more diverse landscapes is thought to be the result of both reduced crop vigor as well as increased natural enemy impact during the overwintering period. Early season populations of Anagrus wasps were found in all vineyards regardless of landscape diversity, implying a strong dispersal capacity from overwintering sites. The Anagrus demonstrated a strong density dependent relationship with E. elegantula and this appeared to drive their densities in vineyards much more so than changes in landscape diversity.