Gazelle : The Palestinian Biological Bulletin (ISSN 0178 – 6288) . Number 116, August 2014, pp. 1-23. | Page 13

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subsequently swarm formation. Interestingly, the nymphal pheromone is
different from the adult one. When exposed to the adult pheromone, hoppers
become confused and disoriented, because they can apparently no longer "smell"
each other, though the visual and tactile stimuli remain. After a few days, the
hopper bands disintegrate and those that escape predation become solitary
again. It is possible that this effect could aid locust control in the future.
During quiet periods, called recessions, desert locusts are confined to a 16million-square-kilometer belt that extends from Mauritania through the Sahara
Desert in northern Africa, across the Arabian Peninsula, and into northwest
India. Under optimal ecological and climatic conditions, several successive
generations can occur, causing swarms to form and invade countries on all sides
of the recession area, as far north as Spain and Russia, as far south as Nigeria and
Kenya, and as far east as India and southwest Asia. As many as 60 countries can
be affected within an area of 32 million square kilometers, or approximately 20
percent of the Earth's land surface (Wikipedia).

Desert Locust (Schistocerca gregaria) on Al-Ka’ba Kiswah in Makkah Al Mukarramah.
Photo by: Prof. Dr. Norman Ali Bassam Khalaf-von Jaffa. 02.01.2014.
http://www.flickr.com/photos/50022881@N00/11838012406/
. ‫الجراد الصحراوي ٌُسبح للرحمن خالق الحٌوان على كسوة الكعبة المُشرفة فً مكة المُكرمة . تصوٌر المإلف‬
Gazelle : The Palestinian Biological Bulletin – Number 116 – August 2014