Supported. We know secondary substances are chemicals that aren’t directly involved in growth and metabolism. But they do play important roles in the lives of plants, because they can do things such as attract insects to pollinate and defend against predation from insects.

Not supported, because we have no evidence that “most” (over half) plants that have defense mechanisms against insects are still eaten by a wide variety of insects. Although we have evidence that some plants are still eaten by some insects despite their defense mechanisms, we have no reason to think this is true about “most” plants with defense mechanisms, or that they’re eaten by a “wide” variety of insects.

We have no reason to think there are any insects that can identify certain groups of plants by means other than taste or smell. Although the author mentions that some insects can come to identify plants by “flavors or odors,” she doesn’t mention identification through other means besides these.

The author never provides evidence of scientists’ beliefs about many secondary substances that are toxic to insects. She never indicates scientists think any kind of secondary substance has evolved “independently in various unrelated species of plants” or that they have survived in only few species.

The author never suggests there exist toxic substances produced by plants that are not secondary substances. Nor does she suggest that there is any relationship between these substances and secondary substances.