Tropical rain forests contain diverse communities of organisms with many interesting relationships. One such relationship connects parasitic fungi and their insect hosts. A type of parasitic fungus, called Ophiocordyceps unilateralis, disperses spores onto the forest floor, but cannot successfully grow on the ground. The fungus requires specific conditions and must grow inside of a specific ant species, called the host, to reproduce. The ants, various species of carpenter ant, make nests in the trees.

O. unilateralis feeds on and grows inside the insect host, and within a few days the fungus affects the insect’s brain. The insect exhibits unusual behaviors such as wandering away from the colony to where light and humidity favor fungal growth. Just before dying, the insect bites into and firmly attaches itself to a plant. Then, the fungus slowly grows outward from the dead insect’s head, producing a pod of spores that eventually bursts open. The spores fall to the ground, restarting the life cycle of the fungus.

Though this relationship may sound gruesome, researchers note that these parasitic fungi may help maintain biodiversity in the tropical rain forest. Some parasitic fungi may be host-specific, meaning that a fungus species only infects a particular type of insect. Scientists have observed that if an insect population begins to grow, more fungal infections occur, and then the insect population levels off again. This relationship may prevent overpopulation of the habitat by any one insect species.

Multiple Choice Item: 1 point value

Question Overview:You must select the correct specific textual evidence to support a given argument in this quest ion. First, you must understand the log ic of the argument that parasit ic fungi offer severely limited potent ial as insecticides that target many kinds of insects. Understanding this reasoning requires you to analyze the text and determine which of four facts from the passage provides the best support for the argument.

Answer Rationale:

Option A is incorrect. If you selected option A, you may have focused on the fact that the passage does indicate that the fungi reproduce inside an insect's body. However, this fact does not support the argument because the location of reproduction is not a factor in determining the fungi's limitations as an insecticide.

Option B is incorrect . If you selected option B, you may have focused on the second sentence of paragraph 2, which does state that fungal growth has an effect on insects' behavior. However, the passage does not state that fungal growth entirely controls the insect's behavior. Also, the fungi's potential as an insecticide is not related to the control of behavior.

Option c is correct. If you selected option c, you noticed that the second sentence of GZI paragraph 3 states that some parasitic fungi only infect a particular type of insect. As a result of this fact, it would not be effective to use parasitic fungi as a general insecticide, since they do not affect large populations of insects.

Option D is incorrect. If you selected option D, you may have focused on the fourth sentence of paragraph 2, which does state that pods grow from an insect's head. However, t his fact has no effect on the fungi's ability to act as an insecticide.