Locust Plague: One of the Worst Agricultural Disasters 蝗災(zāi)

中國(guó)國(guó)際電視臺(tái)

The locust outbreak is affecting large parts of South Asia and the African continents. Massive swarms of locusts have been destroying farmland and threatening millions of lives. Even troops and planes have been mobilized in the Horn of Africa region to fight the most serious plague in decades.

How can an insect with an average mass of 2 grams be so destructive？

Locust plagues often come with serious drought. The insect prefers to lay eggs in dry and loose soil with a lower moisture content. During dry seasons， the groundwater level falls offering more loose soil for the locusts to reproduce. Nearly 5，000 clusters of eggs can be found within a square meter， with more than 100 eggs per cluster.

The reproduction rate of some species is two to five times per year， which adds to the enormous figure. On the dry and sparse grassland， more locusts mean less living space. When the population reaches a certain density under suitable conditions， serotonin in their brains drives them from being solitary to gregarious. They “migrate” together to find new food sources in more moist areas， thus causing an outbreak.

In addition， global warming means warmer winters， therefore more hibernating eggs can survive and hatch in the spring， raising the possibility of the plague next year.

The desert locust is one of the most dangerous of the species. It is the main culprit of the plague that has hit eastern Africa.

Desert locusts can travel between 100 and 200 kilometers per day. A single swarm can cover up to 1，200 square kilometers and can contain between 40 and 80 million locusts per square kilometer.

How many times have humans suffered from locust plagues？

In history， locust plagues have been one of the three worst agricultural natural disasters， alongside flooding and drought.

During the last two millennia， more than 170 outbreaks have been recorded in China. Statistics from 2003 to 2016 show that the land hit by locust outbreaks reached 286 million hectares in China.

In 2004， northern and western Africa experienced the largest infestation of locusts in more than 15 years. It cost 400 million dollars to fight against the plague， and the harvest losses were worth almost 2.5 billion dollars.

Late March 2013， nearly 50 percent of Madagascar was infested by locusts， with each swarm consisting of more than one billion bugs.

Is there no way to stop the locusts？

At present， the primary method of controlling locust infestations is with insecticides sprayed from the ground or the air. That being said， in some less economically developed areas insecticides are unaffordable， let alone the machines and planes needed to spread them.

But there are also biological pest control measures. The locust has natural enemies such as predatory wasps and flies， birds and reptiles.

Every May， swarms of locusts hit northwestern Chinas Xinjiang Uygur Autonomous Region.

In 2019， nearly 200，000 rosy starlings stopped over Hami City in Xinjiang. The birds protected 54 million kilograms of grass from locusts， saving herdsmen 1.6 million yuan and at least 720，000 yuan for buying pesticides.

This biocontrol method has proved effective and requires less human intervention.

Are locusts of no use at all？

The term “l(fā)ocust” is the name given to certain species of short-horned grasshoppers in their swarming phase. They are convenient for use in research and the study of zoology. Like the fruit fly， it is a suitable school laboratory animal.

Locusts are edible. They are considered a delicacy in many African， Middle Eastern and Asian countries.

China has yet to come out of the shadow of locust plagues， according to Kang Le， a research fellow of the Institute of Zoology， Chinese Academy of Sciences. Locusts destroy crops at the estuary of the Yellow River， and the grasslands in Xinjiang and Inner Mongolia autonomous regions.

But it is wrong to overkill them. The overuse of insecticides may control the bug situation in an area for now， but it takes longer for the damaged environment to recuperate. Also， the insect always has its rightful place in the food chain and in the ecosystem.

蝗災(zāi)暴發(fā)正影響著南亞大部和非洲大陸大部分地區(qū)。大批蝗蟲摧毀農(nóng)田，數(shù)百萬人生計(jì)遭受威脅。“非洲之角”地區(qū)甚至調(diào)派了軍隊(duì)和飛機(jī)對(duì)抗數(shù)十年來最嚴(yán)重的災(zāi)情。

一只平均重量只有2克的昆蟲為何具有如此強(qiáng)大的破壞力？

蝗災(zāi)常常伴隨旱災(zāi)而來。蝗蟲喜在含水量較低、干燥疏松的土壤中產(chǎn)卵。在旱季，地下水位下降，土質(zhì)更加疏松，利于蝗蟲繁殖。1平方米土壤中能發(fā)現(xiàn)近5000個(gè)卵塊，每個(gè)卵塊有100多個(gè)卵粒。

某些種類的蝗蟲每年可繁殖二到五代，致使其數(shù)量大增。在干燥稀疏的草原地區(qū)，蝗蟲數(shù)量越多，意味著其生存空間越小。在適當(dāng)條件下，當(dāng)蝗蟲密度達(dá)到一定程度時(shí)，蝗蟲大腦中的血清素會(huì)促使其從散居型轉(zhuǎn)變?yōu)槿壕有?。它們?huì)一起向更潮濕的地區(qū)“移民”，尋找新的食源，從而引發(fā)蝗災(zāi)。

此外，全球變暖帶來暖冬，因此更多越冬蟲卵得以存活并在春季孵化，增加了來年蝗災(zāi)暴發(fā)的可能性。

沙漠蝗蟲是最危險(xiǎn)的蝗蟲之一，是東非地區(qū)蝗災(zāi)的罪魁禍?zhǔn)住?/p>

沙漠蝗蟲每天可飛行100至200公里。單一蟲群可覆蓋1200平方公里，每平方公里的蝗蟲數(shù)量可達(dá)4000萬至8000萬只。

人類迄今遭受過幾次蝗災(zāi)？

歷史上，蝗災(zāi)與水災(zāi)和旱災(zāi)并稱三大農(nóng)業(yè)自然災(zāi)害。

過去2000年中，中國(guó)共記載了170余次蝗災(zāi)。2003年至2016年統(tǒng)計(jì)數(shù)據(jù)顯示，中國(guó)蝗災(zāi)發(fā)生面積達(dá)2.86億公頃。

2004年，非洲北部和西部地區(qū)遭遇了至少15年來最大的一次蝗災(zāi)，抗災(zāi)費(fèi)用高達(dá)4億美元，災(zāi)情造成價(jià)值近25億美元的收成損失。

2013年3月末，馬達(dá)加斯加近50%的地區(qū)遭受蝗災(zāi)，每個(gè)蟲群的蝗蟲數(shù)量超過10億。

沒有辦法阻止蝗災(zāi)暴發(fā)嗎？

目前，防治蝗災(zāi)的主要方法是從地面或空中噴灑殺蟲劑。話雖如此，但一些經(jīng)濟(jì)欠發(fā)達(dá)地區(qū)連殺蟲劑都買不起，更不要說用來噴灑殺蟲劑的設(shè)備和飛機(jī)了。

不過，還有生物治蝗的方法?；认x有很多天敵，例如掠食性黃蜂、蠅類、鳥類和爬行動(dòng)物。

每年5月，會(huì)有大批蝗蟲侵襲中國(guó)西北部的新疆維吾爾自治區(qū)。

2019年，近20萬只粉紅椋鳥遷徙至新疆哈密市。這些椋鳥保護(hù)了5400萬公斤牧草免受蝗蟲侵害，使牧民避免了160萬元的經(jīng)濟(jì)損失，還省下了至少72萬元購(gòu)買殺蟲劑的費(fèi)用。

實(shí)踐證明，這一生物防治方法頗為有效，且不需要多少人工干預(yù)。

蝗蟲一無是處嗎？

“蝗蟲”這一術(shù)語(yǔ)是某些短角蝗科動(dòng)物在集群期的統(tǒng)稱，便于調(diào)研和動(dòng)物學(xué)研究時(shí)使用。像果蠅一樣，蝗蟲適用于學(xué)校實(shí)驗(yàn)。

蝗蟲可以食用，是非洲、中東和亞洲許多國(guó)家餐桌上的美味。

中國(guó)科學(xué)院動(dòng)物研究所研究員康樂稱，中國(guó)尚未擺脫蝗災(zāi)陰影。蝗蟲會(huì)破壞黃河入?？诘霓r(nóng)作物以及新疆維吾爾自治區(qū)和內(nèi)蒙古自治區(qū)的草原。

然而，過度殺滅蝗蟲并不可取。過量使用殺蟲劑或許當(dāng)下可以控制某個(gè)地區(qū)的蝗災(zāi)，但會(huì)導(dǎo)致該地區(qū)環(huán)境受損，恢復(fù)期更長(zhǎng)。另外，食物鏈和生態(tài)系統(tǒng)中始終應(yīng)有蝗蟲的一席之地。? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?□

（譯者單位：復(fù)旦大學(xué)）