Xylophage insects, Cicadomorpha: Order Hempitera, are potential vectors for the bacterium Xylella fastidiosa, causal agent of bacterial leaf scorch of oak.  Cicadomorpha populations in oaks were surveyed in Mercer, Middlesex, and Somerset counties, New Jersey during 2002-2006.  Yellow sticky trap cards were hung in oak tree canopies to monitor insect population dynamics, and pyrethrin fogging of tree canopies was used for comparison. The most frequently collected potential insect vectors were Hemiptera:  Cicadellidae:  Graphocephala versuta and G. coccinea; and Membracidae: Telamona querci, T. concave, T. tiliae, Ophiderma definita, and Archasia galeata.  Cicadellinae xylophages occurred throughout the growing season while the membracids peaked in early summer.  Higher Cicadomorpha populations were found in apparently healthy (asymptomatic) oak trees than in diseased trees.  Xylella fastidiosa was isolated from treehoppers, and PCR procedures were used to detect the bacterial presence in insects.