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Phylloxera and the grapevine: a sense of common purpose?
School of Biological Sciences, The University of Reading, Whiteknights, Reading RG6 6AS, UK
* To whom correspondence should be addressed. Fax: +44 118 3788160. E-mail: n.h.battey{at}reading.ac.uk
Received 10 February 2005; Accepted 13 October 2005
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Abstract |
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 Top Abstract IntroductionA gall mythReferences |
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The purpose of life is its continuation: survival is the reason things live. Here we explore this ‘basic’ of biology, by reference to the extraordinary life-cycle of the aphid-like pest phylloxera, and the complexity of its relationship with its host the grapevine. The effort and ingenuity that phylloxera employs to continue itself leads to a doubt that survival alone is sufficient reason. It has frequently been suggested that the reduction of life to a catalogue of facts (by science) creates this doubt, because it robs existence of its essence (which is something other than its mechanics). The part that science is said to steal is what Robert Pirsig calls Quality—the harmonious balance of things. Pirsig seems to imply that this is something inherent in things—and independent from us. A more mundane explanation is that the difference between facts and the complete reality is us—the tendency of mind to connect freely between different kinds of information. This possibility is briefly illustrated here by a myth based on the facts of phylloxera.
Key words: Evolution, grapevine, Phylloxera, plant–insect interactions
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Introduction |
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TopAbstractIntroductionA gall mythReferences |
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Daktulosphaira vitifoliae (Fitch), also known as phylloxera (Fig. 1), devastated the French wine industry when introduced from North America in the 19th century. It has more recently threatened Californian viticulture and is monitored intensively in many parts of the world. For example, in southern Australia, where vine growing is vital and very successful, aerial infrared photography is used to assess spread of the disease The phylloxera insect is typically confined to its root-living form in commercial vineyards, but its activities can, nevertheless, lead rapidly to destruction of the vines. The only effective solution is to graft the susceptible, wine-producing species Vitis vinifera on to rootstocks of American vine species that co-evolved with phylloxera and can therefore resist or tolerate it. The discovery of this rootstock-mediated treatment for phylloxera revolutionized the viticulture industry, making grafted vines the norm (Fig. 2).
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Peritymbia is another name for phylloxera. It was coined by Westwood during the early stages of discovery and description of the insect, and alludes to the fact that the fundatrix nymph builds a gall that is both her home and her tomb, because she never leaves it.
It's not life she craves, but its continuation
The complete life cycle of phylloxera is passed successively on leaves and tendrils above ground, and on the roots, and its facts can be summarized as follows.
A sexuparous nymph hatches in response to cooling weather in the autumn. She develops wings, emerging from below ground to lay on leaves eggs that hatch as males or females. Male and female mate, and the female lays a winter egg in splits in the bark. In spring, the egg hatches to a fundatrix nymph, a female that returns to the leaf or tendril, and there builds a gall.
It's not life she craves, but its continuation
The gall is created in response to secretions from the fundatrix. These secretions are said to include auxin, although this could be of plant origin, and they cause the inner cells of the leaf or tendril to expand upwards, around where the insect sits (Fig. 3). The plant hairs grow coarse and long across the entrance to the gall, barring access but allowing the fundatrix, now matured to an adult, to lay several hundred eggs. Then she dies.
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It's not life she craves, but its continuation
The hatchlings can leave and establish their own galls, or remain and lay within their mother's gall. Each of three to four parthenogenetic generations lays eggs to yield by midsummer 5000 million descendants of the fundatrix. Then migrant hatchlings return below ground, where they build galls on roots, lay eggs, and multiply. Eventually, an egg hatches as a sexuparous nymph which returns to the leaves.
It's not life she craves, but its continuation
Why? A gall myth is presented in the box in which the gall is more than the insect's home and her tomb. The gall is a symbol, more significant than individual life: it is continuation, the potential for complete connection. The myth gives a glimpse of a Quality that we may crave but Biology suggests we should do without.
From the inside, you see clearly that the phylloxera gall is a half-world, half-plant and half-insect. Fed by gloomy green light it is moist, damp, hair-enclosed, built by the genes, proteins and carbohydrates of the plant but under instruction from the insect. So entwined are insect and vine, you imagine they were once one creature. Guttation fluid produced from vine leaves on warm, moist nights fell as fine, sticky rain. The droplets turned to insect eggs on descending to the soil. The journey back to the leaf is not just a search for light and for food, but a return to the insect's beginning. On reaching the leaf, the mother phylloxera, fundatrix, founder of each repeating cycle, buries her mouthparts in the plant. Sucking and secreting, she converses with it, relaying a blueprint of how she wants the gall built. Auxin, amino acids, perhaps some simple ions—these are shared signals, a code that drives leaf growth up and around the fundatrix, protecting and feeding her. The process suggests a plan, a complicity between insect and plant; their purpose is one day to re-unite.
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Acknowledgements |
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We are very grateful to Paul Hatcher (The University of Reading) and Richard Napier (Warwick-HRI) for helpful comments and suggestions.
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References |
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TopAbstractIntroductionA gall mythReferences |
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Cornu M. 1878. Etudes sur la Phylloxera vastatrix. Mémoires présentés... à l'Académie des Sciences de l'Institut de France XXVI, 43–175.
Crespi B, Worobey M. 1998. Comparative analysis of gall morphology in Australian gall thrips: the evolution of extended phenotypes. Evolution 52, 1686–1696.[CrossRef]
Granett J, Walker MA, Kocsis L, Omer AD. 2001. Biology and management of grape phylloxera. Annual Review of Entomology 46, 387–412.[CrossRef][Web of Science][Medline]
Lewin R. 1993. California's lousy vintage. New Scientist 17 April, 27-31.
Ordish G. 1972. The great wine blight. London: JM Dent & Sons.
Pirsig RM. 1974. Zen and the art of motorcycle maintenance: an inquiry into values. London: Vintage.
Stone GN, Schonrogge K. 2003. The adaptive significance of insect gall morphology. Trends in Ecology and Evolution 18, 512–522.[CrossRef]
Wapshire AJ, Helm KF. 1987. Phylloxera and Vitis: an experimentally testable coevolutionary hypothesis. American Journal of Enology and Viticulture 38, 216–222.
Westwood JO. 1869. New vine diseases. Gardeners' Chronicle and Agricultural Gazette 30 January, 109.
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