Sometimes there is no more effective means of controlling an

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
(5) effectively controlled by a predatory mite of the
genus Typhlodromus. Cyclamen mites infest
strawberry plants; they typically establish themselves
in a strawberry field shortly after planting, but their
populations do not reach significantly damaging
(10) levels until the plants’ second year. Typhlodromus
mites usually invade the strawberry fields during the
second year, rapidly subdue the cyclamen mite
populations, and keep them from reaching
significantly damaging levels.

(15) 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
(20) develop into fertile females. Cyclamen mites lay three
eggs per day over the four or five days of their
reproductive life span; Typhlodromus lay two or three
eggs per day for eight to ten days. Seasonal
synchrony of Typhlodromus reproduction with the
(25) growth of prey populations and ability to survive at
low prey densities also contribute to the predatory
efficiency of Typhlodromus. During winter, when
cyclamen mite populations dwindle to a few
individuals hidden in the crevices and folds of leaves
(30) in the crowns of the strawberry plants, the predatory
mites subsist on the honeydew produced by aphids
and white flies. They do not reproduce except when
they are feeding on the cyclamen mites. These
features, which make Typhlodromus well-suited for
(35) exploiting 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
(40) 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
(45) mite. Throughout the study, populations of cyclamen
mites remained low in plots shared with
Typhlodromus, but their infestation attained
significantly damaging proportions on predator-free
plants.

(50) 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
(55) predators were eliminated by parathion, but they did
not attain such levels in untreated plots. When
cyclamen mite populations began to increase in an
untreated planting, the predator populations quickly
responded to reduce the outbreak. On average,
(60) cyclamen mites were about 25 times more abundant
in the absence of predators than in their presence.

1. Which one of the following most accurately expresses the main point of the passage?

(A) Control of agricultural pests is most effectively and safely accomplished without the use of pesticides, because these pesticides can kill predators that also control the pests.
(B) Experimental verification is essential in demonstrating the effectiveness of natural controls of agricultural pests.
(C) The relationship between Typhlodromus and cyclamen mites demonstrates how natural predation can keep a population of agricultural pests in check.
(D) Predation by Typhlodromus is essential for the control of cyclamen mite populations in strawberry fields.
(E) Similarity in mode and timing of reproduction is what enables Typhlodromus effectively to control populations of cyclamen mites in fields of strawberry plants.


2. Based on the passage, the author would probably hold that which one of the following principles is fundamental to long-term predatory control of agricultural pests?

(A) The reproduction of the predator population should be synchronized with that of the prey population, so that the number of predators surges just prior to a surge in prey numbers.
(B) The effectiveness of the predatory relationship should be experimentally demonstrable in greenhouse as well as field applications.
(C) The prey population should be able to survive in times of low crop productivity, so that the predator population will not decrease to very low levels.
(D) The predator population’s level of consumption of the prey species should be responsive to variations in the size of the prey population.
(E) The predator population should be vulnerable only to pesticides to which the prey population is also vulnerable.


3. Which one of the following is mentioned in the passage as a factor contributing to the effectiveness of Typhlodromus as a predator?

(A) its ability to withstand most insecticides except parathion
(B) its lack of natural predators in strawberry fields
(C) its ability to live in different climates in different geographic regions
(D) its constant food supply in cyclamen mite populations
(E) its ability to survive when few prey are available


4. Suppose that pesticide X drastically slows the reproductive rate of cyclamen mites and has no other direct effect on cyclamen mites or Typhlodromus. Based on the information in the passage, which one of the following would most likely have occurred if, in the experiments mentioned in the passage, pesticide X had been used instead of parathion, with all other conditions affecting the experiments remaining the same?

(A) In both treated and untreated plots inhabited by both Typhlodromus and cyclamen mites, the latter would have been effectively controlled.
(B) Cyclamen mite populations in all treated plots from which Typhlodromus was absent would have been substantially lower than in untreated plots inhabited by both kinds of mites.
(C) In the treated plots, slowed reproduction in cyclamen mites would have led to a loss of reproductive synchrony between Typhlodromus and cyclamen mites.
(D) In the treated plots, Typhlodromus populations would have decreased temporarily and would have eventually increased.
(E) In the treated plots, cyclamen mite populations would have reached significantly damaging levels more slowly, but would have remained at those levels longer, than in untreated plots.


5. It can be inferred from the passage that the author would be most likely to agree with which one of the following statements about the use of predators to control pest populations?

(A) If the use of predators to control cyclamen mite populations fails, then parathion should be used to control these populations.
(B) Until the effects of the predators on beneficial insects that live in strawberry fields are assessed, such predators should be used with caution to control cyclamen mite populations.
(C) Insecticides should be used to control certain pest populations in fields of crops only if the use of natural predators has proven inadequate.
(D) If an insecticide can effectively control pest populations as well as predator populations, then it should be used instead of predators to control pest populations.
(E) Predators generally control pest populations more effectively than pesticides because they do not harm the crops that their prey feed on.


6. The author mentions the egg-laying ability of each kind of mite (lines 20–23) primarily in order to support which one of the following claims?

(A) Mites that reproduce by parthenogenesis do so at approximately equal rates.
(B) Predatory mites typically have a longer reproductive life span than do cyclamen mites.
(C) Typhlodromus can lay their eggs in synchrony with cyclamen mites.
(D) Typhlodromus can reproduce at least as quickly as cyclamen mites.
(E) The egg-laying rate of Typhlodromus is slower in the presence of cyclamen mites than it is in their absence.


7. Which one of the following would, if true, most strengthen the author’s position regarding the practical applicability of the information about predatory mites presented in the passage?

(A) The individual Typhlodromus mites that have the longest reproductive life spans typically also lay the greatest number of eggs per day.
(B) The insecticides that are typically used for mite control on strawberry plants kill both predatory and non predatory species of mites.
(C) In areas in which strawberry plants become infested by cyclamen mites, winters tend to be short and relatively mild.
(D) Typhlodromus are sometimes preyed upon by another species of mites that is highly susceptible to parathion.
(E) Typhlodromus easily tolerate the same range of climatic conditions that strawberry plants do.


8. Information in the passage most strongly supports which one of the following statements?

(A) Strawberry crops can support populations of both cyclamen mites and Typhlodromus mites without significant damage to those crops.
(B) For control of cyclamen mites by another mite species to be effective, it is crucial that the two species have the same mode of reproduction.
(C) Factors that make Typhlodromus effective against cyclamen mites also make it effective against certain other pests of strawberry plants.
(D) When Typhlodromus is relied on to control cyclamen mites in strawberry crops, pesticides may be necessary to prevent significant damage during the first year.
(E) Strawberry growers have unintentionally caused cyclamen mites to become a serious crop pest by the indiscriminate use of parathion.