阻止できるかバッタの大群襲来、カギ握るのはフェロモン　研究

【東京ＡＦＰ＝時事】世界では今年、新型コロナウイルス感染に加えて、バッタの大群襲来による農作物の深刻な被害が大きなニュースとなっている。こうした壊滅的な害をもたらすバッタの群れは、なぜ形成されるのか──秘密はフェロモンにあるとする研究結果が12日、英科学誌ネイチャーに発表された。（写真はパキスタン・シンド州で、バッタの大群を追い払う農業従事者ら）
　この研究によれば、同じ種類のバッタが何匹か近距離に集まると、ある化学物質が放出され、まるで魅惑的な香水のように互いを誘引する。誘われて寄ってきたバッタも同じ化学物質を放出するため、連鎖的な誘引反応が起きるという。
　中国科学院の康楽教授らの研究チームは、バッタの中でも最も広範囲に分布するトノサマバッタに注目し、放出する複数の化合物を分析した。
　すると、特に「４-ビニルアニソール（４ＶＡ）」と呼ばれる化合物が放出されると周囲のバッタを引き寄せ、群れに集まるバッタが多ければ多いほど、４ＶＡの放出量が増えることが分かった。
　研究によると、トノサマバッタはたった４匹を同じケージに入れただけで、それぞれが４ＶＡを放出し始めた。研究チームはさらに、バッタがフェロモンに反応する様子を観察し、触角の特定部位に４ＶＡを検出する機能が備わっていることを突き止めた。
　この検出機能に必要な遺伝子を特定し、遺伝子操作で鍵となる遺伝子「Ｏｒ３５」を欠いたトノサマバッタを生み出したところ、このバッタは「野生のトノサマバッタと比較して、４ＶＡに誘引されなかった」という。
　この発見に基づき、遺伝子操作によってバッタの群生を食い止めたり、４ＶＡの放出を追跡することで大群の発生を予測したり、４ＶＡを利用したわなでバッタをおびき寄せて駆除したりといった蝗害（こうがい）対策の可能性が期待されている。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2020/08/14-13:53）

The coronavirus isn't the only plague making headlines this year -- locusts are devastating crops in several parts of the world, and now scientists are discovering why the pest forms destructive swarms.
On its own, a locust is fairly harmless. But so-called solitary locusts can undergo a metamorphosis, changing colour and joining together with millions of others in catastrophic clouds that strip fields.
So what prompts locusts to transform from solitary to gregarious?
A study published Wednesday in the journal Nature reveals the secret lies in a pheromone.
Almost like an irresistible perfume, the chemical compound is emitted by locusts when they find themselves in proximity to just a few others of their kind.
The chemical attracts other locusts, who join the group and also begin emitting the scent, creating a feedback loop that results in enormous swarms.
The discovery offers several tantalising possibilities, including genetically engineering locusts without the receptors that detect the swarming pheromone, or weaponising the pheromone to attract and trap the insects.
The study comes as record numbers of locusts devour crops in east Africa and threaten the food supply in Pakistan.
It focused on the migratory locust, the most widely distributed species of the insect, and examined several compounds produced by the bug.
It found that one in particular -- 4-vinylanisole, or 4VA -- appeared to attract locusts when emitted, and that the more locusts flocked together, the more 4VA they emitted.
The team, led by Le Kang, a professor at the Chinese Academy of Sciences, found solitary locusts began releasing 4VA when just four were placed together in a cage.
The team then examined how the locusts picked up the scent, and isolated the part of the locust antennae responsible for detecting the swarming pheromone.
And from there, they found the gene necessary for the detection process and produced genetically modified locusts lacking the key Or35 gene.
The mutant locusts lost their attraction to 4VA compared with the wild-type locusts, the study said.
- Chemical interference -
The discoveries open up several possibilities for tackling the voracious pests, including using genetic modification, or tracking 4VA production to predict where swarms may be forming.
There are other avenues too, including weaponising the chemical, by using a synthetic form of it to bait traps to catch locusts.
Kang and his team tried this, setting up traps in both controlled settings and in the field, and in both cases found the locusts were effectively lured.
Optimisation and adjustment are necessarily required from the experiments to practical application, Kang told AFP.
But he said the traps were significantly efficient and could be a comparatively easy first application of the research.
Leslie Vosshall, head of Rockefeller University's Laboratory of Neurogenetics and Behavior, said perhaps the most exciting application would be finding a chemical that would block reception of 4VA.
The discovery of such a molecule might provide a chemical antidote to insect aggregation and cause locusts to 'stand down' and return to their peaceful, solitary way of life, she wrote in a review commissioned by Nature.
Vosshall pointed out that there are still several unknowns, including whether 4VA is the only thing that causes swarm formation, and whether other locust species respond similarly to the compound.
Kang said genetic modification of locusts might offer sustainable and green control but acknowledged such a project would require large-scale and long-term efforts.
This is an approach for long-term control of locusts, and needs strict biological security evaluation before application.