The virulence of a planthopper, Nilaparvata lugens (Stål) biotype 3, reared on rice cultivar ASD7and of N. lugens colonies collected on Mindanao Island in the southern Philippines and reared on the widely grown commercial cultivars IR36 and IR42 was compared. Based on plant damage, insect weight, population growth, and feeding activity, the Mindanao N. lugens colonies reared on IR36 and IR42 were more virulent than biotype 3, although ASD7, IR36, and IR42 have the bph2 gene for N. lugens resistance. These results clearly indicate that in the screening of breeding lines for resistance to N. lugens, it is important to use insect populations reared on cultivars similar to those grown in farmers’ fields. Failure to do so may result in the release of a cultivar that is susceptible to the N. lugens field population
