生物谷综合：当臭蝽在大豆田里大快朵颐时，这些可恶的家伙仍不忘在田里四处产卵，而这一切的背后都是一个神秘帮凶在作祟。研究人员发现，一种生活在臭蝽内脏中的微生物能够控制其繁殖，进而使害虫在田间产下数百万枚虫卵。如果除去这种微生物，则臭蝽的数量将直线下降，从而有效缓解其对农作物的危害。然而如果向一种无害臭蝽体内注射相同的微生物，则这种昆虫的数量将会激增，并最终加入咀嚼大豆的大军。这一发现为研究昆虫的进化提供了新的线索，但它能否有助于农业学家开发出保护农作物丰产的新方法尚难以估量。
科学家曾经假设，农作物害虫进化后的基因能够帮助它们确定庄稼的位置。如今，日本东京大学的研究人员通过一项简单的试验得出了一个令人惊讶的结果。他们并没有从臭蝽(Megacopta punctatissima)的基因下手，而是调整了寄居在其内脏中的共生细菌。研究小组将在实验室中培育的M. punctatissima体内的细菌清除干净，之后将这些细菌移植进这种臭蝽的表亲——M. cribraria——的内脏中。在正常情况下，M. cribraria很少以大豆为食。
试验结果表明，这两种昆虫的角色产生了转换——突然间，M. punctatissima在实验室中的产卵数量出现了大幅度下降，而M. cribraria的产卵数量则开始激增。参与该项研究的昆虫学家Takema Fukatsu认为：“是生理学因素而非行为学因素导致了这一结果。”显然，这种微生物在两种臭蝽的生活周期中均扮演了一个至关重要的角色——无论其寄居在哪种昆虫体内，都会增强宿主的繁殖能力。一旦M. cribraria变成这种细菌最主要的宿主，它便成为对大豆最有威胁的害虫。研究人员在上周的英国《皇家学会学报B卷》（Proceedings of the Royal Society, Series B）网络版上报告了这一研究成果。
Fukatsu指出，研究小组正在测定这种臭蝽内脏微生物的基因组序列，从而搞清其运作机制。他说，相同的技术还可以用于研究那些寄生于蚜虫、舌蝇、白蚁和其他害虫体内的细菌。如果能够除去这些细菌，将使这些昆虫对农作物的危害大打折扣。
美国印第安纳州西拉法叶市波尔多大学的昆虫学家Tom Turpin认为，这一研究成果对于进化生物学而言非常有趣。但它能否成为控制害虫的一种有效手段“还需要综合生物学、社会学以及伦理学因素进行考虑”。Turpin举例说，通过向农田喷洒抗生素消灭内部的细菌能够杀死这些害虫，但还要意识到，这些药物残留也将对以庄稼为食的人类构成威胁。（援引科学时报）
原始出处:
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 t-fukatsu@aist.go.jp
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.
