1. First, second, and sixth authors: Texas A&M University-Kingsville Citrus Center, 312 N. International Blvd., Weslaco, TX 78599; third author: USDA APHIS PPQ CPHST, Mission Laboratory, Edinburg, TX 78541; and fourth and fifth authors: University of Texas Rio Grande Valley, Department of Mathematics, 1201 W. University Drive, Edinburg, TX 78539.