The use of plant diversification (e.g., mixed cropping, cover crops, border plants, intercrops, etc. ) to protect a primary crop from insect transmitted viral diseases is often referred to as barrier cropping. Specific plants used to mitigate virus incidence in a cash crop are frequently called protector plants. The potential use of protector plants to reduce the density of aphid vectors and incidence of aphid-borne nonpersistent virus in zucchini, Cucurbita pepo L. was evaluated during 2003, 2005, and 2006 on Oahu, HI. Cover crops, buckwheat Fagopyrum esculentum Moench and white clover Trifolium repens L., or sunn hemp, Crotolaria juncea L. and an intercropped vegetable, okra Abelmonchus esculentus (L.), were evaluated for their potential use as protector plants. Results of the field experiments showed that densities of alatae aphids in water pan traps did not differ significantly among treatment habitats during three field experiments. However, the percentage of zucchini plants showing virus symptoms was significantly lower in diculture than monoculture habitat during all 3 yr. Results from field and laboratory experiments support the hypothesis that protector plants reduced the incidence of Papaya ringspot virus-watermelon strain by acting as virus sinks and that the three cover crops were more effective in reducing Papaya ringspot virus-watermelon spread than okra.