PrepTest 53, Section 4, Question 24
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 themselves in a strawberry field shortly after planting, but their populations do not reach significantly damaging 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.
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 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 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 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 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 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 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.
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 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, cyclamen mites were about 25 times more abundant in the absence of predators than in their presence.
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 themselves in a strawberry field shortly after planting, but their populations do not reach significantly damaging 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.
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 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 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 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 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 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 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.
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 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, cyclamen mites were about 25 times more abundant in the absence of predators than in their presence.
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 themselves in a strawberry field shortly after planting, but their populations do not reach significantly damaging 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.
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 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 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 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 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 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 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.
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 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, cyclamen mites were about 25 times more abundant in the absence of predators than in their presence.
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 themselves in a strawberry field shortly after planting, but their populations do not reach significantly damaging 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.
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 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 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 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 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 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 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.
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 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, cyclamen mites were about 25 times more abundant in the absence of predators than in their presence.
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?
If the use of predators to control cyclamen mite populations fails, then parathion should be used to control these populations.
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.
Insecticides should be used to control certain pest populations in fields of crops only if the use of natural predators has proven inadequate.
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.
Predators generally control pest populations more effectively than pesticides because they do not harm the crops that their prey feed on.
Explanations
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