Answer: D. feeds on the leaves of crops

The image shows a caterpillar, which is the larval stage of a moth. Caterpillars are known to feed on the leaves of plants, which can cause significant damage to crops. Therefore, the economic importance of the larva is that it feeds on the leaves of crops, which can have a negative impact on agriculture and food production.
 

Option A, "is eaten by birds," is not the correct answer because it does not address the economic importance of the larva. While it is true that caterpillars are eaten by some bird species, this fact does not have significant economic implications.

On the other hand, option D, "feeds on the leaves of crops," is the correct answer because this behavior can cause significant economic damage. Caterpillars can consume large amounts of a crop's foliage, leading to reduced yields and lower quality produce. As a result, farmers and agricultural industries spend significant amounts of money and resources to control caterpillar populations and minimize crop damage.