The diet of Heliothis subflexa caterpillars consists entirely of fruit from plants of the genus Physalis. These fruit do not contain linolenic acid, which is necessary to the growth and maturation of many insects other than H. subflexa. Linolenic acid in an insect’s diet is also necessary for the production of a chemical called volicitin. While most caterpillar species have volicitin in their saliva, H. subflexa does not.
Summary
Most caterpillar species have volicitin in their saliva.
If an insect produces volicitin, then it must have linolenic acid in its diet.
Many insects need linolenic acid to grow.
*Physalis* plants don’t contain linolenic acid.
*H. subflexa* caterpillars only eat *Physalis* plants.
*H. subflexa* caterpillars don’t have volicitin in their saliva.
Very Strongly Supported Conclusions
Most caterpillar species have linolenic acid in their diets.
Most caterpillar species don’t eat only *Physalis* plants.
Many insects can’t grow and mature if they only eat *Physalis* plants.
A
H. subflexa caterpillars synthesize linolenic acid within their bodies.
Unsupported. *H. subflexa* caterpillars don’t get linolenic acid from their diets, but this doesn’t necessarily mean that they synthesize it within their bodies. They might just not need any linolenic acid or volicitin.
B
Most species of caterpillar have sources of linolenic acid in their diets.
Very strongly supported. Most species of caterpillar have volicitin in their saliva. And if an insect produces volicitin, then it must have linolenic acid in its diet. So most species of caterpillar have linolenic acid in their diets.
C
Any caterpillar that has linolenic acid in its diet has volicitin in its saliva.
Unsupported. If a caterpillar has volicitin in its saliva, then it must have linolenic acid in its diet. But this doesn’t necessarily mean that if a caterpillar has linolenic acid in its diet, then it must have volicitin in its saliva. (C) reverses the conditional claim.
D
A food source containing linolenic acid would be poisonous to H. subflexa caterpillars.
Unsupported. *H. subflexa* caterpillars only eat plants that don’t contain linolenic acid. But this doesn’t necessarily mean that plants that do contain linolenic acid are poisonous to them. They might just hatch on *Physalis* plants and never move to other plants.
E
No caterpillars other than H. subflexa eat fruit from plants of the genus Physalis.
Unsupported. Most caterpillars have linolenic acid in their diets. But this doesn’t mean that no other caterpillars eat *Physalis* plants. There might be others like *H. subflexa* that only eat *Physalis* plants, or some that eat *Physalis* plants and other plants with linolenic acid.
A
Plants can also absorb heavy nitrogen from a variety of sources other than rainwater.
B
The rate at which heavy nitrogen accumulated in the blood of Ice Age herbivores can be inferred from samples of their bones.
C
The same number of samples was taken from present-day bears as was taken from Ice Age cave bears.
D
Bone samples from present-day bears fed meat-enriched diets exhibit the same levels of heavy nitrogen as do their blood samples.
E
The level of heavy nitrogen in the bones of any bear fed a meat-enriched diet is the same as that in the bones of any other meat-eating bear.