From field surveys, we investigated the relationship between the populations of wintering adults, their feeding on leaflets, the larval populations, and the number of newly emerged adults. The method to be used was the main subject of the research. Wintering adults were trapped using boxes put out every day in different parts of the field. The leaflet notches made by these adults were given a score from 0 to 3. Soil samples were washed with a turbulent overflow process to evaluate larval populations per plant. The state of the nitrogen-fixing root nodules was noted. Emerging summer adults were trapped in the same type of box as the spring ones. The main quantitative relationship was the highly significant correlation between the spring score of adult notches on the leaflets of the first level of leaves and the subsequent larval populations. Other correlations were also analysed. Results are also given on damage caused by the larvae. In French pea crops, an adult score of 3 was related to a mean level of 12 larvae per plant and 90 % of root nodules are destroyed.