Entomologia Experimentaliset Applicata 74:245-251, 1995. 245 @ 1995 Kluwer AcademicPublishers. Printed in Belgium. Mechanisms of resistance to the brown planthopper Nilaparvata lugens in wild rice (Oryza spp.) cultivars R. Velusamy, M. Ganesh Kumar & Y. S. Johnson Thangaraj Edward Department of Agricultural Entomology, Tamil Nadu Agricultural University, Coimbatore 641 003, India Accepted: July 5, 1994 Key words: Insecta, insect resistance, brown planthopper, wild rices, Homoptera, Delphacidae Abstract Three wild rice species and six cultivated rice varieties were evaluated to determine their mechanisms of resistance to Nilaparvata lugens (Stal.). Wild rice species, Oryza officinalis, O. punctata, and O. latifolia and cultivated rices Rathu Heenati (Bph 3), Babawee (bph 4), ARC 10550 (bph 5), Swarnalata (Bph 6), Ptb 33 (bph 2+Bph 3) and the susceptible Taichung Native (TN 1) (no resistance gene ) were included in the study. In a free choice seedbox screening test, wild rice species maintained their high level of resistance through the 48 h exposure to N. lugens nymphs while plant damage ratings of cultivated rice varieties increased with time. Wild rices were non preferred and significantly more individuals settled on susceptible TN 1 followed by cultivated rices. The quantity of food ingested and assimilated by N. lugens on wild rices was less than on cultivated resistant varieties. N. lugens caged on resistant wild rices had slow nymphal development, reduced longevity, low fecundity, and low egg hatchability as compared to N. lugens on cultivated resistant varieties. Introduction The rice brown planthopper Nilaparvata lugens has become a serious threat to rice production in many Asian countries (Dyck & Thomas, 1979). Natural populations of N. lugens in South Asia differ in vir- ulence patterns from those in East and Southeast Asia (Khush et al., 1985). The brown planthoppers in differ- ent countries have been categorized into four biotypes based on differential reactions (Khush et aL, 1985). The brown planthopper populations in South Asia have been variously referred to as the South Asian biotype or biotype 4 (Khush, 1984). The term biotype is used herein in the sense of Gallun & Khush, (1980) and refers to pest populations which differ in their ability to infest rice varieties with specific major genes for resistance. Cultivar resistance has been increasingly recog- nized as being the most desirable and economic con- trol tactic in the management of brown planthopper. To determine the potential value of wild species of rice in conferring resistance to the local populations of N. lugens, three species that were previously identified as highly resistant (Velusamy, 1988) were studied to determine their mechanisms of resistance to N. lugens. Wild rices were compared with five O. sativa varieties having diverse genes for N. lugens resistance. Materials and methods Mechanisms of resistance to the brown planthopper Nilaparvata lugens (Stal.) were studied in three wild rice species, viz., Oryza officinalis, O. punctata, and O. latifolia in comparison with cultivated rices Rathu Heenati, Babawee, ARC 10550, Swarnalata, and Ptb 33 which have known genes for brown plan- thopper resistance (Anwarul Kabir & Khush, 1988). Taichung Native 1 (TN 1) served as susceptible check. All tests were conducted under greenhouse conditions at the Tamil Nadu Agricultural University, Coimbat- ore, India at temperatures ranging from 20-30 ~ The N. lugens population collected from rice fields in Tamil Nadu was maintained on TN 1 for about 10 years (100 generations) prior to tests.