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Insects and flowering plants (Angiosperms) are the dominant
terrestrial organisms and have had a long shared history. Insects depend on plants for food and
shelter. Insects that feed directly on
plant leaves are known as herbivores and include things like caterpillars,
grasshoppers, and aphids. Many other
insects feed on other parts of flowering plants including plant fruits, seeds,
roots, stems, and bark. Plants defend
themselves against various types of insect feeders by using chemicals or by
having defensive structures like leaf hairs and thorns on their stems. Some insects evolve mechanisms to overcome a
certain type of plant’s defenses. For
example, monarch butterfly caterpillars are among the few types of insects that
can feed on milkweed. When an insect
evolves with a plant, the situation is known as co-evolution.  A monarch caterpillar feeding on milkweed.The relationship between plants and insects is not just a one way street. Most flowering plants use insects for reproduction. Insects are attracted to brightly colored and sweet-smelling flowers. While at the flower, they receive a nectar reward. In exchange, they carry the plant’s pollen to the flowers of other plants. This allows plants that are rooted in place to mate with others of their species. Like insects, there are few Angiosperms in marine environments. Also like insects, they face several limitations including having to overcome salty conditions, having to be able to sprout and grow underwater, and having to be able to reproduce. Although a few plants are able to pollinate in a watery environment, most require dry conditions, and insect pollinators.  So, does the long co-evolutionary history of insects and Angiosperms, and the relative absence of angiosperms in the ocean prevent insects from colonizing the ocean? It certainly plays a role. The absence of ocean trees and flowers likely prevents certain orders like the butterflies (Lepidoptera) from expanding into the ocean. However, several groups of flowering plants are successful in marine areas. These plants include mangrove trees which have submerged roots but have their leaves, flowers, and fruits out of the salt water. Mangrove trees support a rich insect fauna. Are there any submerged marine Angiosperms? The answer is yes. Seagrasses of which there are about 50 species are abundant in shallow marine waters. They spend their entire lives submerged beneath the waves where they accomplish growth, flowering, and pollination. But, there are very few marine insects that feed on seagrasses, suggesting that there is some other limitation to insects colonizing the ocean.  Hypothesis 5: the ocean lacks nutrition.Stay lean and green on your way back home. T The Fourth Letter Of the Password |