Methods for making a modified Cry3A toxin are disclosed. Such methods include the insertion of a protease recognition site that is recognized by a gut protease of a target insect, such as corn rootworm, into at least one position of a Cry3A toxin so that a modified Cry3A toxin is thus designed. The coding sequence of the modified Cry3A toxin may be transformed into a host cell and the host cell grown under conditions that allow the host cell to produce the modified Cry3A toxin. The host cell may be a plant cell and the plant may be comprised in a transgenic plant. Thus, the transgenic plant may be used to produce the modified Cry3A toxin.