GENETIC ANALYSIS OF A THRESHOLD TRAIT - DENSITY-DEPENDENT WING DIMORPHISM IN SOGATELLA FURCIFERA (HORVATH) (HEMIPTERA, DELPHACIDAE), THE WHITEBACKED PLANTHOPPER

摘要

The whitebacked planthopper Sogatella furcifera exhibits wing dimorphism. The production of female macropters is most influenced by nymphal population density and is positively density-dependent. Bidirectional wing-form selection was imposed under several nymphal density conditions. Selection for increasing and decreasing the incidence of macroptery was most effective under antagonistic selection, i.e. selection for macroptery was most effective under low density conditions and selection for brachyptery was most effective under crowded conditions. Crossing experiments using the 10th generation of lines selected for macroptery and brachyptery suggest that the wing-form in S. furcifera is a threshold character under polygenic control and is determined by a threshold response to nymphal density. Broad sense heritability of wing-form was at least 0.467. The realized heritability was 0.512 estimated from the lines selected for macroptery and 0.298 from the lines selected for brachyptery. The relationship between wing-form ratio and nymphal density (i.e. reaction norm) was parallel, which proved that there was no genotype-by-environment interaction between wing-form and density.