A releasably engaging plug comprises a plug body having an extension, the outer surface of the extension having at least one projection thereon. A communications interface appends the telephone exchange number of an outgoing communication to include an identifier unique to the communications interface. A sleeve is mounted in a non-rotating manner on the input shaft, the pulley is rotationally mounted on the sleeve and the disk carrier is flanged to the face end of the sleeve. A method for imparting tristeza virus resistance in citrus plants using the DNA molecule of the present invention is also disclosed. Methods for operating the control system are also discussed.