农作物病虫害正在以同变暖的温度相同的步伐朝着地球的两极迈进。这一发现表明，气候变化正在驱动病虫害的迁移，同时对粮食安全问题提出了更大的挑战。
气候变化被认为将导致物种在世界各地的分布变化，即整体远离赤道并向两极平移。生态学家已经在许多野生物种中证实了这样的一种转移，包括一些鸟类和昆虫。
在许多国家，气候变化已经引发了关于粮食安全的强烈关注，而害虫或许会让情况变得更糟。主持这项新研究的英国埃克赛特大学的生态学家Dan Bebber表示：“我们的防御工事，从杀虫剂到杀菌剂都被要求能够对付越来越多的害虫和疾病，但后者却正在进化出针对前者的抗性。”而害虫种群扩张到新的领土无疑增加了这些生物体逃脱人类控制后造成的风险。
而其中最大的威胁来自于真菌和卵菌，它们是相似但分属不同种类的微生物，能够导致植物的病害。几个高毒性的真菌菌株近年来出现在世界各地，而即便在导致爱尔兰大饥荒168年以后，卵菌纲的致病疫霉(Phytophthorainfestans)仍然是各国需要面对的一个永恒问题。
农作物病虫害的全球活动从未得到全面的分析。为了填补这一空白，Bebber及其同事采用了CABI(原名农业生物科学国际中心)提供的历史记录——它们记载了从1822年至今发生在全世界的农作物病虫害。该研究的合作者之一、埃克赛特大学的植物病理学家Sarah Gurr指出：“没有人曾着眼于任何一个这样的数据库。这是第一个此类分析。”
另一位合作者Mark Ramotowski将CABI的样本从8万个记录缩小至26776个记录——研究人员主要聚焦于上世纪60年代之后的时间段，因为这些记录往往是最可靠的。对于612种不同的害虫，研究人员确定了每一种害虫在一个新的国家(或者一个大国的某一地区)被首次发现的年份，并把这作为害虫到达该国或该地区平均纬度的时间。
这项研究的主要弱点在于数据的偏差。研究人员假设，如果没有任何现实趋势，害虫似乎应该朝着赤道运动，而不是两极方向。这是因为与其他国家相比，发达国家拥有的科学资源能够比前者更早地监测到害虫，而发达国家往往位于高纬度地区。随着各国的发展以及对害虫更多的了解，害虫的范围似乎开始向热带地区迁移。
事实上，研究人员发现，农作物害虫以平均每年2.7公里的速度向两极方向迁移，这与全球气候变化的速度非常接近。然而，这一速度在不同的物种乃至同一物种之中也存在巨大变化。真菌、甲虫、蝽、螨虫、蝴蝶以及蛾子表现出了向高纬度地区的明显迁移，而病毒和线虫动物门则向低纬度地区迁移。其他物种没有表现出任何可察觉的改变。
Gurr表示：“许多研究表明，气候变化正在影响野生物种种群的分布规律。而这是第一个表明类似过程正在害虫种群中发生的研究。”她还强调了一个令人担忧的发现，即真菌和卵菌正在以非常快的速度前进——分别为每年7公里和6公里。研究人员在9月1日的《自然—气候变化》杂志上报告了这一研究成果。
英国约克大学生物学家Chris Thomas强调，农作物病虫害整体的运动速度非常近似于由他主持的一项有关野生物种迁徙的荟萃分析的研究结果。他说：“我的第一印象为这是一项非常彻底的研究。”Thomas指出，就像作者所说的，那些看起来向赤道前进的害虫种群——大部分是线虫动物门和病毒——往往是了解最少的，因此它们随后更有可能在发展中国家被发现。（生物谷 Bioon.com）
生物谷推荐的英文摘要
Nature doi:10.1038/nature.2013.13644
Crop pests advancing with global warming
Eliot Barford
Crop pests and diseases are moving towards the poles at about the same speed as warmer temperatures. The finding suggests that climate change is driving their relocation, and raises major concerns about food security.
Climate change is expected to cause changes in the distributions of species around the world, with an overall shift away from the equator and towards the poles. Ecologists have already documented such a shift in many wild species, including some birds and insects1, 2, 3.
The changing climate is raising major concerns about food security in many countries, and pests may contribute to making matters worse. “Our defences, pesticides and fungicides, are being asked to deal with larger and larger numbers of pests and diseases, each of which can evolve fungicide or pesticide resistance,” says ecologist Dan Bebber of the University of Exeter, UK, who led the new study. Expansion of pest populations into new territories increases the risk that these organisms will escape our control.
Among the biggest threats are fungi and oomycetes, similar but distinct groups of microbes, which cause plant diseases. Several highly virulent strains of fungi have emerged in recent years around the world, and the oomycete Phytophthora infestans remains a persistent problem even 168 years after causing the great Irish potato famine4.
Global movement of crop pests had never been comprehensively analysed. To fill this gap, Bebber and his colleagues made use of historical records held by CABI (formerly known as the Centre for Agricultural Bioscience International), which document crop pests and diseases around the world from 1822 to the present. “No one has looked at any of these datasets. This is the first such analysis,” says co-author Sarah Gurr, a plant pathologist also at Exeter.
Co-author Mark Ramotowski, who did his work as a student at the University of Oxford, UK, narrowed the CABI sample down from over 80,000 records to 26,776, focusing on the period since 1960, when they are ilkely most reliable. For 612 different pest species, the researchers identified the first year in which each was observed in a new country (or region for larger countries) and took that to be the date at which the pest reached that country or region’s average latitude.
The main vulnerability of their study was biases in the data. The group hypothesised that, in the absence of any real trend, pests would appear to be moving towards the equator rather than the poles. This is because wealthier countries have the scientific resources to detect pests earlier than others, and wealthier countries tend to be at higher latitudes. As countries develop and study their pests better, the pests’ range could appear to move into the tropics.
Instead, the team found that, on average, crop pests have been moving towards the poles at 2.7 kilometres per year, which is very close to the rate of climate change5. However, the rate of shift varied significantly for different groups and among individual species. Fungi, beetles, true bugs, mites, butterflies and moths showed clear movements to higher latitudes, whereas viruses and nematode worms shifted to lower latitudes. Other groups showed no detectable change.
“Many studies have shown that climate change is affecting the distribution of wild species populations. This is the first one to show that a similar process is happening in pest species,” says Gurr. She highlights the worrying finding that fungi and oomycetes are moving particularly quickly, at 7 and 6 km per year respectively. Her team's study is published today in Nature Climate Change6.
Chris Thomas, a biologist at the University of York, UK, notes that the overall rate of movement is quite similar to that found in a meta-analysis he led on the movement of wild species1. “My first impression is that it looks like a thorough study.” He notes, as do the authors, that those pest groups seen moving towards the equator — largely nematode worms and viruses are the most poorly understood, and therefore the ones most likely to be discovered later in developing countries.
