Insect Production and Secretion of Phytohormones and Impacts on Host Plants

Several phytohormones have been detected in whole-body analyses of insects and in their salivary glands, saliva, and frass. More comprehensive surveys are needed to develop a clear picture of their distribution and abundance in insects, but cytokinins, auxin (indole-3-acetic acid), and abscisic acid appear to be widespread in insects. Other phytohormones, such as salicylic acid, jasmonates, gibberellins, and brassinosteroids, have also been reported, but a full assessment of their distribution and abundance in insects requires further study. Exogenous phytohormones provided by herbivorous insects likely alter source-sink nutrient dynamics in their host plants, modulate host-plant defenses, lead to the induction of plant galls and the vascularization of galls connecting them to the host plant, lead to the development of green islands, and can alter anthocyanin biosynthesis, which in the sun may make galls red.