[Effects of cutting on the population dynamics of main insect pests on alfalfa]

A systematic investigation was made on the effects of cutting on the population dynamics of main insect pests on alfalfa in Dingxi of Gansu Province. The results showed that the effects of cutting varied significantly with the kinds of insect pests. The seasonal average population densities of Therioaphis trifolii, Acyrthosiphon pisum and thrips decreased significantly and maintained at a low level under the first cutting in early June, but less variation was observed under the second cutting in mid-July. Plant bug presented somewhat different picture. In the early period of first cutting, its seasonal average population density decreased significantly but increased then, and was significantly higher in early August, compared with that in uncut field. Opposite with T. trifolii, A. pisum and thrips, the seasonal average population density of plant bug was more affected by second cutting.