Antixenosis and Antibiosis Resistance in Rice Cultivars against Chilo suppressalis (Walker) (Lepidoptera: Crambidae).

The striped stem borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), is an important pest afflicting rice in most rice-growing countries in the world. Deliniating the categories of resistance in rice genotypes under field conditions could be helpful in managment of this pest. Two categories of resistance, antixenosis and antibiosis, were examined in ten popular and diverse rice genotypes of different origin that had been selected for their resistance to the striped stem borer in a previous study. Significant differences were found between genotypes for the number of egg masses, number of eggs, preference index, larval and pupal weight, larval development time, larval survival rate, larval mine length, and leaf trichome density. It was found that the rice genotypes Novator, A7801, and Nemat had the more pronounced antixenosis-type resistance, whereas AB1 and Shirodi had better antiobiosis-type resistance. Interestingly, the rice genotype AN-74 for which Nemat is the parental line showed both types of resistance and could be effectively used in an integrated pest management of the rice striped stem borer.

Nutritional indices and midgut enzymatic activity of Phthorimaea operculella (Lepidoptera: Gelechiidae) larvae fed different potato germplasms.

The effect of 10 potato cultivars and clones on the feeding and digestion of Phthorimaea operculella (Zeller) larvae was evaluated using larval nutritional indices and enzymatic activities. Studies were based on nutritional indices from larvae reared at 25 +/- 1 degrees C, 65 +/- 5% relative humidity, and in complete darkness. The results of nutritional indices showed that conversion efficiency of ingested and digested food in the larvae at the fourth instar was the highest in Savalan cultivar at rates of 22.30 +/- 0.39 and 32.87 +/- 0.69%, respectively, and the lowest were recorded on Morene at rates of 15.83 +/- 0.35 and 21.99 +/- 0.58%, respectively. Among the different potato germplasms tested in the study, the highest proteolytic and amylolytic activities of the larvae, at optimal pH were in Morene with records of 8.204 +/- 0.296 U/mg and 0.071 +/- 0.0004 mU/mg, respectively; and the lowest were recorded in larvae fed on Savalan at 2.740 +/- 0.131 U/mg and 0.028 +/- 0.0001 mU/mg, respectively. It is concluded that Morene was the most unsuitable host for P. operculella.

Karyological study of four species of wheat grass (Agropyron sp.).

Karyological study of four Agropyron species (A. desertorum, A. cristatum, A. pectinoforum and A. imbricatum) showed that these species were tetraploid (2n = 4x = 28) with the base number, x=7. In the studied cells ofA. desertrum, 28 chromosomes with 1 B chromosome and satellite on chromosomes 2 and 4 were exist. The number of chromosomes in studied cells of A. cristatum ranged between 28 and 31 without B chromosome and with satellite on chromosome 3 and 5. In the cells ofA. imbricatum that studied, 28 to 33 chromosomes with 1 to 3 B chromosomes and satellite on chromosome 7 were exist. The number of chromosomes in studied cells of A. pectinoforum ranged between 28 and 29 and 1 B chromosome and satellite on chromosome 3 were exist. Finally in the studded cells of four species 28-33 chromosomes were exist (the various forms ofaneuploid cells). One to three B chromosomes and chromosomes with satellites also observed in these species.