Abstract
The potato aphid Acyrthosiphon solani (KALTENBACH) was reared individually on a leaf of soybean in a plastic cup at 23°C and with a 16hr day length. The lx and mx curves of adults were not significantly different between the apterae and alatae. The intrinsic rate of increase (rm) of apterae was estimated as 0.21. The population growth and the dispersal of the aphid were observed on soybean plants. Six apterous nymphs at the 4th instar were inoculated on different parts of each plant, i.e. the lowest, 2nd or 4th leaf. Regardless of the leaf the aphids were inoculated on, they began to reproduce. When the number of aphids increased to a level of the density on the leaf, the aphids migrated to the above leaf. The migration of the aphids from the leaf or the plant occurred when the number of aphids was maximum and aphids of all developmental stages migrated simultaneously. Immediately after, the leaf died of serious infestation. A small number of adult alatae emerged throughout the period of the experiment, but among them, less than 50% migrated from the plants. The instantaneous rates (r0) of increase on the soybean plants were similar to the value of rm, suggesting that the population growth was not affected seriously by the overcrowding of the aphids.
