Petrov, A. A., and N. P. Sopov. 1948. Conjugated systems. XXXVI. Condensation of some diene hydrocarbons with methacrylic acid and methyl methacrylate.

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The genetics of resistance of several rice cultivars (Oryza saliva L.) to the brown planthopper, Nilaparvata o lugens (Stal), and to the green leafhopper, Nephotettix impicticeps (Ishihara), was studied in the greenhouse. Two testing techniques were developed and employed. In one, 7-day-old seedlings were infested with insects and then classified on the basis of insect injury. In the other a known number of insects were caged on tillers of 6-weekold plants and insect survival was used as the criterion for classification. The resistance of 'Mudgo,' 'Manavari CO22,' and 'Dalwa Sannam MTU15' to the brown planthopper was controlled by single dominant genes that appeared to be allelomorphic. Another cultivar, 'Karsamba Red ASD7,' possessed a single recessive gene for planthopper resistance that was either allelic or closely linked to the locus that conditions resistance in the other three cultivars. The field reaction of F 4 lines of a cross between Mudgo and a susceptible cultivar was strongly correlated with the greenhouse reaction, and aparently the same gene controlled planthopper resistance at different stages of growth. Resistance to the green leafhopper in the cultivars 'Pankhari 203,' 'ASD7,' and 'IR8' also was controlled by single genes that were nonallelic and dominant. The planthopper resistance of Mudgo, and the leafhopper resistance of Pankhari 203 were independently inherited as was the resistance of ASD7 to the two insects.

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Oxalic acid, isolated from leaf sheath extract of rice, has been identified as a potent sucking inhibitor against the brown planthopper. Potassium and sodium oxalate at concentrations of 0.1%–0.2% completely inhibited sucking on a 15% sucrose solution. Of twelve aliphatic acids commonly present in plants, only oxalic, maleic, and trans‐aconitic acids at 0.1%, significantly reduced sucking activity while Krebs cycle acids, such as citric, malic, and succinic, did not have any inhibitory effect. RÉSUMÉ L'ACIDE OXALIQUE COMME INHIBITEUR DE LA SUCCION DE NIPALARVATA LUGENS STÀL, (HOMOPTERE, DELPHACIDAE) L'acide oxalique, isolé des gaines foliaires du riz, a été identifié comme un puissant inhibiteur de la succion de Nilaparvata lugens. Les oxalates de potassium et de sodium aux concentrations de 0,1% et 0,2% inhibent complètement la succion d'une solution de sucrose à 15%. Parmi les douze acides aliphatiques généralement présents dans la plante, seuls les acides oxalique, maleique et trans‐aconique réduisent significativement à 0,1% l'activité de succion, tandis que les acides cycliques comme les acides citrique, malique et succinique n'ont pas d'effet inhibiteur.

Techniques to quantify the feeding activity of Nilaparvata lugens (Still) on rice varieties as based on honeydew excretion are described and their potential as a b.ioassa¥for.bioty~e identification are discussed. Honeydew, excreted on filter paper, was stamed Withnmhydnn and quantified by measuring the area (mm 2) or by weighing. Results were sati~fact<~ry b~t the methods were extremely tedious. Volumetric measurement of honeydew with rrncroplpettes was less sensitive.. The color intensity of one ILliter honeydew streaked on filter paper and treated With 0.001% ninhydrin was determined with a Fujiox™ Densitometer. The method was relatively simple and rapid and was sufficiently precise for biotype identification as based on differential feeding activity.

The rice brown planthopper, Nilaparvata lugens (Stal), a major pest of rice in most of Asia, underwent optimum development at 25 and 29°C, but 33°C was detrimental to all life stages. However, this effect was moderated considerably by rearing the insects at 12-hour alternations of 25° and 33 °C or 29° and 33 °C. While high planthopper populations caused "hopper burn," lower infestations reduced the number of tillers, number of panicles, and total grain weight of the plants. Unfilled grains resulted from infestation during the reproductive growth stage of plants but not from infestation during the vegetative phase. There were distinct differences in the susceptibility of 20 selected varieties to this species. While some of these varieties were less preferred by the insect and showed some antibiosis effects, tolerance to hopper burn appeared to be the major factor in the differences of susceptibility. There were no apparent correlations between the resistance of these varieties to the brown planthopper and their resistance to the rice green leafhopper. The brown planthopper, Nilapan'ata lugens (Stal), I From a thesis submitted by the senior author in partial fulfillment of the requirements of the degree of Master of Science in Entomology, College of Agriculture, University of the Philippines.