Abstract:

The changing population of beet noctuid was monitored on the broccoli farms from 2002 to 2008; the relation between larva quantity and Advanced age larva quantity was determined as well as the relation between Advanced age larva amount per plant and loss rate of damaged plants. The results indicated that the changes of beet noctuid population showed bimodal curve. Its peaks were from April to May and from August to November, which is consistent with the growing stages of broccoli plants on the fields. And there was a very notable linear correlation between Advanced age larva amount per plant during seedling period and loss rate of damaged plants. Its regression was Y=23.126X+1.5803 (n=17,r=0.8075**). Balanced and green prevention principle applied, the allowed economic loss was tested and the damage rate per plant was 3.09%（≈3%）. Then according to the model of relation between larva quantity and advanced age larva quantity, X=0.3204M+0.0378(n=17，r=0.8903**), it is suggested that the prevention and killing index for broccoli is 20 larvae per 100 plants.