Comprehension : Comprehension

Q 402 / 466

UPSC CSE Prelims 2012

Chemical pesticides lose their role in sustainable agriculture if the pests evolve resistance. The evolution of pesticide resistance is simply natural selection in action. It is almost certain to occur when vast numbers of a genetically variable population are killed. One or a few individuals may be unusually resistant (perhaps because they possess an enzyme that can detoxify the pesticide). If the pesticide is applied repeatedly, each successive generation of the pest will contain a larger proportion of resistant individuals Pests typically have a high intrinsic rate of reproduction, and so few individuals in one generation may give rise to hundreds or thousands in the next, and resistance spreads very rapidly in a population.
This problem was often ignored in the past, even though the first case of DDT (dichloro diphenyltrichloroethane) resistance was reported early as 1946. There is exponential increase in the numbers of m vertebrates that have evolved resistance and in the number of pesticides against which resistance has evolved. Resistance has been recorded in every family of arthropod pests (including dipterans such as mosquitoes and house flies, as well as beetles, moths, wasps, fleas, Lice and mites) as well as well as in weeds and plant pathogens, Take the Alabama leaf-worm, a moth pest of cotton, as an example. It has developed resistance in one or more regions of the world to Aldrin, DDT, dieldrin, endrin, lindane and toxaphene.
If chemical pesticides brought nothing but, problem-if their use was intrinsically and acutely unsustainable — then they would already have fallen out of widespread use. This has not happened. Instead, their rate of production has increased rapidly. The ratio of cost of benefit for the individual agricultural producer has remained in favour of pesticide use. In the USA insecticides have been estimated to benefit the agricultural products to the tune of around $5 for every $1 spent.
Moreover, in many poorer countries, the prospect of imminent mass starvation, or of an epidemic disease, are so frightening that the social and health cost of using pesticides have to be ignored. In general, the use of pesticides is justified by objective measures such as lives saved, ‘economic efficiency of food production’’ and total food produced. In these very fundamental senses, their use may be described as sustainable. In practice, sustainability depends on continually developing new pesticides that keep at least one step ahead of the pests pesticides that are less persistent, biodegradable and more accurately targeted all the pests.
How do pesticides act as agents for the selection of resistant individuals in any pest population?

  1. It is possible that in a pest population the individuals will behave differently due to their genetic makeup.
  2. Pests do possess the ability to detoxify the pesticides.
  3. Evolution of pesticide resistance is equally distributed in pest population.

Which of the statements given above is/are correct?

EXPLANATION

Correct Option (2)

Statement 1 is correct. The passage explicitly states that the evolution of pesticide resistance is "natural selection in action" and "is almost certain to occur when vast numbers of a genetically variable population are killed." It further notes that "One or a few individuals may be unusually resistant (perhaps because they possess an enzyme that can detoxify the pesticide)." This indicates that genetic variability within a pest population leads to differential survival and behavior in the presence of pesticides, forming the basis for resistance evolution.

Statement 2 is correct. The passage provides a specific mechanism for resistance: "One or a few individuals may be unusually resistant (perhaps because they possess an enzyme that can detoxify the pesticide)." This confirms that some pests, or individuals within a pest population, possess the ability to detoxify pesticides, which contributes to their resistance.

Incorrect Options:

Statement 3 is incorrect. The passage describes resistance as emerging in "one or a few individuals" and then spreading rapidly through successive generations, leading to a "larger proportion of resistant individuals." This process clearly indicates that the evolution of pesticide resistance is not equally distributed in the pest population; rather, it originates in a subset and then propagates.