生物谷綜合：當臭蝽在大豆田里大快朵頤時，這些可惡的家伙仍不忘在田里四處產(chǎn)卵,，而這一切的背后都是一個神秘幫兇在作祟。研究人員發(fā)現(xiàn),，一種生活在臭蝽內臟中的微生物能夠控制其繁殖,，進而使害蟲在田間產(chǎn)下數(shù)百萬枚蟲卵。如果除去這種微生物,，則臭蝽的數(shù)量將直線下降,，從而有效緩解其對農作物的危害。然而如果向一種無害臭蝽體內注射相同的微生物,，則這種昆蟲的數(shù)量將會激增,，并最終加入咀嚼大豆的大軍,。這一發(fā)現(xiàn)為研究昆蟲的進化提供了新的線索，但它能否有助于農業(yè)學家開發(fā)出保護農作物豐產(chǎn)的新方法尚難以估量,。
科學家曾經(jīng)假設,，農作物害蟲進化后的基因能夠幫助它們確定莊稼的位置。如今,，日本東京大學的研究人員通過一項簡單的試驗得出了一個令人驚訝的結果,。他們并沒有從臭蝽(Megacopta punctatissima)的基因下手，而是調整了寄居在其內臟中的共生細菌,。研究小組將在實驗室中培育的M. punctatissima體內的細菌清除干凈,，之后將這些細菌移植進這種臭蝽的表親——M. cribraria——的內臟中。在正常情況下,，M. cribraria很少以大豆為食。
試驗結果表明,，這兩種昆蟲的角色產(chǎn)生了轉換——突然間,，M. punctatissima在實驗室中的產(chǎn)卵數(shù)量出現(xiàn)了大幅度下降，而M. cribraria的產(chǎn)卵數(shù)量則開始激增,。參與該項研究的昆蟲學家Takema Fukatsu認為：“是生理學因素而非行為學因素導致了這一結果,。”顯然，這種微生物在兩種臭蝽的生活周期中均扮演了一個至關重要的角色——無論其寄居在哪種昆蟲體內,，都會增強宿主的繁殖能力,。一旦M. cribraria變成這種細菌最主要的宿主，它便成為對大豆最有威脅的害蟲,。研究人員在上周的英國《皇家學會學報B卷》（Proceedings of the Royal Society, Series B）網(wǎng)絡版上報告了這一研究成果,。
Fukatsu指出，研究小組正在測定這種臭蝽內臟微生物的基因組序列,，從而搞清其運作機制,。他說，相同的技術還可以用于研究那些寄生于蚜蟲,、舌蠅,、白蟻和其他害蟲體內的細菌。如果能夠除去這些細菌,，將使這些昆蟲對農作物的危害大打折扣,。
美國印第安納州西拉法葉市波爾多大學的昆蟲學家Tom Turpin認為，這一研究成果對于進化生物學而言非常有趣,。但它能否成為控制害蟲的一種有效手段“還需要綜合生物學,、社會學以及倫理學因素進行考慮”。Turpin舉例說,，通過向農田噴灑抗生素消滅內部的細菌能夠殺死這些害蟲,，但還要意識到,，這些藥物殘留也將對以莊稼為食的人類構成威脅。（援引科學時報）
原始出處:
Proceedings of The Royal Society B
ISSN: 0962-8452 (Paper) 1471-2954 (Online)
Issue: FirstCite Early Online Publishing
DOI: 10.1098/rspb.2007.0620
Obligate symbiont involved in pest status of host insect
Takahiro Hosokawa1, 2, Yoshitomo Kikuchi1, 3, Masakazu Shimada2 & Takema Fukatsu1, 2, *
1Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8566, Japan
2Department of Systems Sciences, University of Tokyo, Tokyo 153-8902, Japan
3Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269-3125, USA
*Author and address for correspondence: Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8566, Japan [email protected]
Received 10 May 2007; Accepted 25 May 2007
Abstract
The origin of specific insect genotypes that enable efficient use of agricultural plants is an important subject not only in applied fields like pest control and management but also in basic disciplines like evolutionary biology. Conventionally, it has been presupposed that such pest-related ecological traits are attributed to genes encoded in the insect genomes. Here, however, we report that pest status of an insect is principally determined by symbiont genotype rather than by insect genotype. A pest stinkbug species, Megacopta punctatissima, performed well on crop legumes, while a closely related non-pest species, Megacopta cribraria, suffered low egg hatch rate on the plants. When their obligate gut symbiotic bacteria were experimentally exchanged between the species, their performance on the crop legumes was, strikingly, completely reversed: the pest species suffered low egg hatch rate, whereas the non-pest species restored normal egg hatch rate and showed good performance. The low egg hatch rates were attributed to nymphal mortality before or upon hatching, which were associated with the symbiont from the non-pest stinkbug irrespective of the host insect species. Our finding sheds new light on the evolutionary origin of insect pests, potentially leading to novel approaches to pest control and management.
Keywords: Megacopta punctatissima; Megacopta cribraria; Candidatus Ishikawaella capsulata; symbiont capsule; plant adaptation; pest evolution
Figure 1 Pest and non-pest plataspid stinkbugs. (a) Newborn nymphs of Megacopta punctatissima probing capsules for symbiont acquisition. Arrows and arrowheads indicate symbiont capsules and eggshells, respectively. (b) Pest species r symbiont acquisition. Arrows and arrowheads indicate symbiont capsules and eggshells, respectively. (b) Pest species M. punctatissima. (c) Non-pest species Megacopta cribraria. Normal adult females with their original symbiont (control) and manipulated adult females whose symbiont was experimentally replaced by the heterospecific one (replaced) are shown. Scale bars, 1mm.
