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  3. A man-made chemical that attracts male gypsy moths by duplicating the natural attractant of female gypsy moths has been patented

A man-made chemical that attracts male gypsy moths by duplicating the natural attractant of female gypsy moths has been patented

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问题     A man-made chemical that attracts male gypsy moths by duplicating the natural attractant of female gypsy moths has been patented as No. 3,018,219.
    Dr. Martin Jacobson of Silver Spring, Md., assigned patent rights to the U. S. Government as represented by the Secretary of Agriculture. The chemical can be used to detect gypsy moth infestations, as well as to control the insects.
    The gypsy moth does serious damage to forest and shade trees in New England and eastern New York State. The caterpillars, or larvae, of gypsy moths eat the leaves of trees, often causing death by a single attack. Losses of hardwood trees have been estimated at tens of millions of dollars from a 20-year study.
    Gypsy moths were prevented from spreading to other U. S. forest areas by using the natural attractant of the female to detect infestations, then spraying with chemicals such as DDT to kill the insects.
    Since the lure could previously be obtained only by clipping the last two abdominal segments of the virgin female moth, extracting the segments with benzene and then processing to stabilize the chemical, the procedure was expensive. Another difficulty was that, as the gypsy moth population declined, it became increasingly hard to obtain the females needed for lure production.
    Dr. Jacobson overcame both these difficulties by discovering a synthetic method for making the female’s attractant chemical. The chemical is known as 12-acetoxy-l-hydroxycis-9- octadecene. It is so potent that the fraction of a drop produced by the female is 200,000 times more than the amount needed to catch a mate. The synthetic chemical is also very powerful--it works in amounts about equivalent to one drop in a box car.
    The flightless female gypsy moth mates only once a year and, as soon as she does, an enzyme switches off production of the sex attractant. The winged male, however, call mate several times and it is because of this that the chemical is being used for pest control.
    By using a mixture of attractant and DDT in traps lined with a sticky substance, enough males can be caught to reduce the gypsy moth population substantially.
Prior to Dr. Jacobson’s synthetic drug, scientists found difficulty in controlling the pest because ______.
选项 A、the natural drug was unavailable
B、female moths hid from the scientists
C、extracting the natural drug involved a complicated process
D、the gypsy moth population declined
答案C
解析 在雅各布森博土的合成药物出现之前，科学家们发现很难控制这种害虫，因为提取天然的药物需要一个复杂的过程。根据第五段，以往获得引诱剂的唯一方法是剪掉未授精而产卵的雌性舞毒蛾腹部的最后两个体节，拔出含有苯的体节，然后进行加工，从而达到使药物稳定的目的，其过程要付出很大的代价。
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