Reading ComprehensionDifficulty: Hard

PT124 S4 P4 Q21 Explanation

Cyclamen Mites

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TopicsPrincipleScience

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Passage

Sometimes there is no more effective means of controlling an agricultural pest than giving free rein to its natural predators. A case in point is the cyclamen mite, a pest whose population can be effectively controlled by a predatory mite of the genus Typhlodromus. Cyclamen mites infest strawberry plants; they typically establish year, rapidly subdue the cyclamen mite populations, and keep them from reaching significantly damaging levels.

Typhlodromus owes its effectiveness as a predator to several factors in addition to its voracious appetite. Its population can increase as rapidly as that of its prey. Both species reproduce by parthenogenesis—a mode of reproduction in which unfertilized eggs develop into fertile females. Cyclamen mites lay three eggs per day over the the seasonal rises and falls of its prey, are common among predators that control prey populations.

Greenhouse experiments have verified the importance of Typhlodromus predation for keeping cyclamen mites in check. One group of strawberry plants was stocked with both predator and prey mites; a second group was kept predator-free by regular application of parathion, an insecticide that kills the predatory species but does not affect the cyclamen with Typhlodromus, but their infestation attained significantly damaging proportions on predator-free plants.

Applying parathion in this instance is a clear case in which using a pesticide would do far more harm than good to an agricultural enterprise. The results were similar in field plantings of strawberries, where cyclamen mites also reached damaging levels when predators were eliminated by parathion, but they did not attain were about 25 times more abundant in the absence of predators than in their presence.

What this question is testing

Principle

Your task

Pin down exactly what the question asks about the passage — a detail, the author's view, the structure, or the main point — before looking at the choices.

Common trap

Answers that restate a true detail from the passage but don't answer the specific question being asked.

Winning move

Anticipate the answer in your own words from the passage, then find the choice that matches that prediction.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
21.

Based on the passage, the author would probably hold that which one of the following principles is fundamental to long-term predatory

Answer choices

  1. Reversal23% picked this

    The reproduction of the predator population should be synchronized with that of the prey population, so that the number of predators surges just prior

    In the case of T's and C's, the prey's population surges first, and then T swoops in and eats them.

  2. Unsupported5% picked this

    The effectiveness of the predatory relationship should be experimentally demonstrable in greenhouse as well

    This is pulling details from the 3rd and 4th paragraphs (greenhouse and field applications), but we can tell that the keywords from the question stem are connecting to the last sentence of the 2nd sentence. We have no textual way to attach the 3rd and 4th paragraph ideas to the concept of "fundamental to long-term control". The textual support for fundamental characteristics of long-term control has to come from the "features" referred to in that end of 2nd paragraph sentence.

  3. Reversal6% picked this

    The prey population should be able to survive in times of low crop productivity, so that the predator population will not

    In the story of the C's and T's, the predator survives in times of low prey population, when the latter have dwindled during winter.

  4. Correct62% picked this

    The predator population's level of consumption of the prey species should be responsive to variations in the size

    Why this is right

    This describes the dynamic population levels we heard about in the 2nd paragraph. Middle of that paragraph describes "seasonal synchrony of T reproduction with the growth of C population and ability to survive at low C density".

    Skill tested: Principle · how this choice captures the passage's function is the move to repeat next time.

  5. Too Strong: "only" Unsupported4% picked this

    The predator population should be vulnerable only to pesticides to which the prey population

    This idea doesn't make much common sense. The predator and the pesticide have the same goal -- kill the prey. If a farmer wanted to take advantage of both the natural predator and a pesticide, she would want the pesticide to only kill the prey, so that the predator can also kill the prey. The pesticide parathion was an example of a pesticide that only killed the predator population. It was discussed because it was used in an experiment that would see how the prey would fare if we used a pesticide to kill off the predator.

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