The Hessian fly, the wheat midge, and the rice gall midge are among the most important insect pests of cereals worldwide. Plant resistance is the most effective method of control; however, the use of resistant cultivars leads to the development of biotypes that can survive on formerly resistant cultivars. How these insects hijack their host plant’s development to feed and protect the larvae is unknown. However, it is believed salivary secretions from the larvae are the signals that cause abnormal plant growth in susceptible plants or elicit a defense response in resistant plants. We have created a database of genes expressed in the salivary glands of these insects. From this database we have been able to identify genes that are similar between the species and genes that are unique to each species. These results are allowing us to understand how these pests hijack a susceptible plant’s development as well as the signals a resistant plant recognizes to defend itself.