Swarms of millions of locusts have, since Biblical times and untilour very own day, been considered a “plague” of major proportions, withthe creatures destroying every growing thing in their path.
Until now, it was thought that the directions of these swarms werepredominantly directed by prevailing winds. Now, Hebrew University ofJerusalem scientists have shown that a physiological trait of thesegrasshoppers –- namely their polarization vision -- provides them witha built-in source of “surface analysis” – a discovery that could pavethe way for efforts to effectively combat this periodic scourge bycontrolling their natural inclination to fly over land rather thanwater.
The desert locusts, known scientifically as Schistocerca gregaria,are able to swarm for great distances and in numbers measuring in themillions. During the locust invasion of November 2004 in Israel, itappeared that a swarm came in an easterly direction over Sinai up tothe Gulf of Eilat, then turned northward without crossing the water.Only when the swarm reached the northern tip of the gulf did some ofthem turn again east in the direction of Aqaba and other areas ofJordan, as well as straight north over southern Israel.
This observation led to examination by scientists of the HebrewUniversity of Jerusalem Department of Evolution, Systematics andEcology and the Interuniversity Institute for Marine Sciences in Eilatto examine how the locusts were able to identify the gulf water andknew not to fly over it. The research focused on the ability of thelocusts to identify polarized light. This is a trait which is lackingin humans but exists among other species, such as fish and insects.
The research was conducted by Dr. Nadav Shashar, who is considered aleading world expert on polarized sight, working with two students,Shai Sabah and Noa Aharoni. The research was published in a recentissue of the journal of the British Royal Society, Biology Letters, aswell as in the science news sections of the journals Science and Nature.
“In order to examine if the locusts are using polarized light indetermining their flight path, we examined individual locusts’reactions in situations in which polarized and non-polarized light wasreflected from various surfaces. We were able to prove that the locustsavoided flying over areas which were reflecting polarized light -- forexample from mirrors or plastic surfaces.”
The sea reflects polarized light much more than dry land (whichreflects mainly diffused, non-polarized light), enabling a distinctionto be made between the two.“When the locusts are presented with a situation of choice betweensurfaces reflecting either polarized or diffused light, they exercisetheir preference to fly over the (dry land) area of diffused light,”said Dr. Shashar. This is a survival instinct, since if they flew overa body of water, the locusts would be deprived of both nourishment anda place to land and rest.
This research, said Dr. Shashar, could be important in providinginformation that would be useful in developing means for “deceiving”the locusts and deterring them from flying over agricultural lands andcausing the great damage that ensues.
One way of doing so might be through more extensive use of plasticsheeting as shields to create the reflection of the polarized lightthat the locusts avoid.
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