THE humble but industrious ant has long served as a metaphor for the economic virtues of simplicity,
parsimony and diligence. But in the case of weaver ants in Africa, this description may be more than just a
metaphor. According to a study published in the latest issue of the Journal of Economic Entomology, by
Paul van Mele of the Consultative Group on International Agricultural Research and his colleagues, African
mango farmers could increase their harvests by as much as two-thirds with the help of these doughty
insects.
Mangoes in Africa, as elsewhere, often fall prey to fruit flies, which destroy about 40% of the continent's
crop. In fact, fruit flies are so common in African mangoes that America has banned their import
altogether, to protect its own orchards. African farmers, meanwhile, have few practical means to defend
their fruit. Chemical pesticides are expensive. And even for those who can afford them they are not that
effective since, by the time a farmer spots an infestation, it is too late to spray. Added to that, spraying
tall trees is a much more complicated and unhealthy business than treating low-growing fruit and
vegetables.
Agricultural scientists have also looked at controlling fruit flies with parasitic wasps. But the most common
ones kill off only about one fly in 20, leaving plenty of survivors to go on the rampage. Lethal traps baited
with fly-attracting pheromones are another option. But they, too, are expensive. Moreover, all these
methods require farmers to detect the presence of fruit flies, and to identify them as the main threat to
their crop—no mean feat when most of the action is taking place in dense, leafy canopies ten metres off
the ground. Instead, most farmers simply harvest their fruit early, when it is not yet fully ripe. This makes
it less vulnerable to the flies, but also less valuable.
Farmers whose trees are teeming with weaver ants, however, do not need to bother with any of this. In a
survey of several orchards in Benin, Dr van Mele and his colleagues found an average of less than one
fruit-fly pupa in each batch of 30 mangoes from trees where weaver ants were abundant, but an average
of 77 pupae in batches from trees without weaver ants. The weaver ants, it turns out, are very thorough
about hunting down and eating fruit flies, as well as a host of other pests. The only drawback is the ants'
painful bite, which can be avoided by harvesting fruit with poles, rather than climbing trees.
Weaver ants have been used for pest control in China and other Asian countries for centuries. The practice
has also been adopted in Australia. But Dr van Mele argues that it is particularly suited to Africa since
weaver ants are endemic to the mango-growing regions of the continent, and little training or capital is
needed to put them to work. All you need do is locate a suitable nest and run string from it to the trees
you wish to protect. The ants will then quickly find their way to the target. Teaching a group of farmers in
Burkina Faso to use weaver ants in this way took just a day, according to Dr van Mele. Those farmers no
longer use pesticides to control fruit flies, and so are able to market their mangoes as organic to eager
European consumers, vastly increasing their income. The ants, so to speak, are on the march.
译文:
非洲织叶蚁如何使种植芒果的农民免遭损失
地位卑微但却勤勤恳恳的蚂蚁长期被喻为朴素、节俭以及勤奋的代名词。然而就生长在非洲的织叶蚁来说，这样的描述可能不只是一个隐喻。国际农业研究顾问组保罗.迈勒博士和他的同事在《经济昆虫学期刊》发表了一项最新的研究结果。该研究结果显示，非洲的芒果农可以利用这些强大的小昆虫提高三分之二左右的收成。
同世界上的其他地方类似，种植在非洲的芒果常常成为果蝇的牺牲品，这将给庄稼收成带来40%左右的损失。事实上，非洲芒果树普遍受果蝇侵袭，这导致美国已经禁止完全进口非洲芒果树来保护其自身的果园不受其危害。同时，非洲农民几乎没有实际有效的办法保卫他们的果实。
化学农药十分昂贵，然而就算那些农民可以买得起，也很难起到什么效果。因为等到农民发现果蝇侵袭再去喷射农药，那就太迟了。另外，相对于给矮生水果和蔬菜喷射农药来说，处理高大的树木是一件多么复杂且不利于健康的工作。
农业学家也尝试利用寄生蜂控制果蝇的侵害，但最常见的寄生蜂群也只能消灭20只果蝇中的其中一只而已，剩下大量的果蝇继续横冲直撞、危害农田。用吸引果蝇的信息素做成致命的陷阱又是另外一个消灭果蝇的方法，但这实在是太贵了。此外，这些方法都要求果农及时发现果蝇的存在并确认它们是农作物的主要威胁——当大多数的操作手段都用在距地面十米高度有茂密多叶覆盖植被上时，会取得很好的效果。取而代之的是，大部分的果农在果实还没完全成熟的时候就过早采摘了。这会使得果蝇对果实的敏感度降低，但也会降低果实的价值。
然而，自家果树中满是织叶蚁的农民就不需要被这问题困扰。迈勒博士和他的同事在对贝宁湾一些果园的调查中发现，大量织叶蚁聚集的树上每一批产出的30个芒果平均只有少于一个的果蝇蛹，而在没有织叶蚁的树上却能发现77个果蝇蛹成批存在。经证实，织叶蚁能十分彻底地找到并消灭果蝇以及其他害虫。唯一的不利因素就是被这些蚂蚁叮咬会很疼。与其爬上树摘果实还不如用杆子打下来，这可以使农民不被蚂蚁叮咬。用织叶蚁控制害虫的方法在中国和其他亚洲国家已流传几个世纪了 。澳大利亚也已经采用这种办法。但迈勒博士认为，织叶蚁是非洲芒果生长地区所特有的，而且几乎不需要进行训练和投入资金就可以让它们工作，因此这种方法非常适合非洲地区使用。你要做的就是在你希望保护的树上放置一个适宜的鸟巢并用细线圈住它。于是，蚂蚁将很快找到它们的攻击对象。据迈勒博士所说，仅需要短短一天时间就能够使布基纳法索的农民学会这样利用织叶蚁除害虫。那些农民不再使用农药来抑制果蝇，因此他们能够把有机又健康的芒果推销到欧洲消费者手上，这极大地增加了他们的收入。织叶蚁可以说正在迅速发展。