 Organic molecules such as sugars, amino acids, certain hormones, and even messenger RNAs are transported in the phloem through sieve tube elements.Phloem is also used as a popular site for oviposition and breeding of insects belonging to the order Diptera, including the fruit fly "Drosophila montana".Because phloem tubes are located outside the xylem in most plants, a tree or other plant can be killed by stripping away the bark in a ring on the trunk or stem.