與某些有機農(nóng)業(yè)的支持者所持的觀點恰好相反,，與化肥相比，天然肥料在保護農(nóng)作物免遭害蟲侵襲方面并不一定做得更好,，有時甚至要更糟,。這正是英國研究人員在一項為時兩年的實驗中獲得的發(fā)現(xiàn)。這一研究成果表明,，農(nóng)民需要根據(jù)不同的植物類型有選擇地使用各種肥料,。
由于使用了天然成分，有機農(nóng)業(yè)在最近的幾十年中變得越來越流行,。例如,，這種耕作方式的支持者認為，與石化產(chǎn)品相比,，牛糞對環(huán)境的危害遠比前者要小得多,。一些提倡者也曾宣稱，與人造肥料相比,，有機肥料能夠幫助農(nóng)作物更好地抵御病蟲害。這是因為植物從有機肥料中吸收氮和其他營養(yǎng)物質(zhì)的速度更為緩慢,，因此以這些營養(yǎng)物質(zhì)為食的害蟲幼蟲則不得不需要面對一段艱苦的時光,。
之前對此問題進行的研究被證明是缺乏說服力的，因此英國倫敦皇家學院的研究人員與英國其他兩家研究機構(gòu)的科學家聯(lián)手,，就3種害蟲——兩類蚜蟲及一種蛾子——如何對在卷心菜上施用的有機肥料和人造肥料作出反應進行了研究,。研究小組將雞糞以及來自豆科植物和苜蓿的其他綠色肥料，還有商業(yè)生產(chǎn)的硝酸銨,，分別以同樣的濃度施加在卷心菜上,。這項實驗在多個田間試驗點持續(xù)了兩個生長季節(jié)。
研究人員最終取得了令人驚訝的結(jié)果,。與被施用了有機肥料的卷心菜相比,，一種蛾子（Plutella xylostella）更喜歡施加了人造肥料的植物，它們在后者上產(chǎn)的卵通常是前者的4倍,。一種蚜蟲（Myzus persicae）同樣也喜歡商業(yè)肥料——與添加了有機肥料的植物相比,，它們在使用了硝酸銨的卷心菜上產(chǎn)的卵是前者的兩倍。然而還有一種蚜蟲（Brevicoryne brassicae）卻喜歡用雞糞澆注的卷心菜,，它們在這些蔬菜與用化肥培植的蔬菜上的產(chǎn)卵比為3∶1,。研究人員在最新出版的英國《皇家學報B》上報告了這一研究成果。
參與此項研究的昆蟲學家Simon Leather指出,，這項研究為我們帶來的教訓便是,，肥料與植物之間復雜的化學反應是很難被預測的，某些肥料可能會擊退一些害蟲，但同時卻會吸引另一些害蟲,。他說：“一個尺碼不可能適合所有的身材,。”
英國紐卡斯爾大學的生物學家Gordon Port對此表示贊同，他稱這項研究是一項“堅實的”工作,。Port認為,，接下來需要搞清的便是害蟲在自然界的敵人——例如蚜蟲的天敵瓢蟲，以及蛾子的天敵黃蜂和蜘蛛——如何對這兩種不同的肥料產(chǎn)生反應,。（生物谷Bioon.com）
生物谷推薦原始出處：
Proceedings of the Royal Society B November 11, 2009, doi: 10.1098/rspb.2009.1631
Varying responses of insect herbivores to altered plant chemistry under organic and conventional treatments
Joanna T. Staley1,*, Alex Stewart-Jones2, Tom W. Pope2,?, Denis J. Wright1, Simon R. Leather1, Paul Hadley3, John T. Rossiter1, Helmut F. van Emden3 and Guy M. Poppy2
1Division of Biology, Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot, Berkshire SL5 7PY, UK
2School of Biological Sciences, University of Southampton, Hampshire SO16 7PX, UK
3School of Biological Sciences, University of Reading, Whiteknights, Reading, Berkshire RG6 6AH, UK
The hypothesis that plants supplied with organic fertilizers are better defended against insect herbivores than those supplied with synthetic fertilizers was tested over two field seasons. Organic and synthetic fertilizer treatments at two nitrogen concentrations were supplied to Brassica plants, and their effects on the abundance of herbivore species and plant chemistry were assessed. The organic treatments also differed in fertilizer type: a green manure was used for the low-nitrogen treatment, while the high-nitrogen treatment contained green and animal manures. Two aphid species showed different responses to fertilizers: the Brassica specialist Brevicoryne brassicae was more abundant on organically fertilized plants, while the generalist Myzus persicae had higher populations on synthetically fertilized plants. The diamondback moth Plutella xylostella (a crucifer specialist) was more abundant on synthetically fertilized plants and preferred to oviposit on these plants. Glucosinolate concentrations were up to three times greater on plants grown in the organic treatments, while foliar nitrogen was maximized on plants under the higher of the synthetic fertilizer treatments. The varying response of herbivore species to these strong differences in plant chemistry demonstrates that hypotheses on defence in organically grown crops have over-simplified the response of phytophagous insects.
