Concepts of Population Dynamics and Estimation of Boll Weevil Populations1

Abstract

Information on recovery, movement, and mortality of the boll weevil, Anthonomus grandis Boheman, was obtained from field-cage studies in North Carolina during 1962. The average recovery of weevils on cotton plants was 65.5%, and 88.8% of the recovered weevils were found on squares, flowers, and bolls. Variation from the average recovery (65.5%) in excess of 10% occurred in about 1 of 4 examinations. This variation appeared to be due to many factors acting together rather than to single factors such as generation, age, sex, and number of weevils or date and time of day of examination. However, plant maturity enhanced recovery. Migration by first-generation weevils (mostly females) was indicated on July 28 and 30, but the tendency to escape did not persist. The mortality rate of overwintered and second-generation weevils was approximately 2% per day, while that of first-generation weevils was 1%. The estimation of weevil populations at 7-day intervals is based upon (1) adult weevils recorded multiplied by appropriate correction factor which yields number of weevils present, (2) squares with egg punctures multiplied by percentage adult emergence from caged, flared squares which yields number of weevils expected to emerge during 2-week period, (3) progressive mortality of overwintered and first-generation adults at 14% and 7%, respectively, prior to emergence of second generation or beginning of migration, after which constant mortality of approximately 25% is used for all weevils. The expected population is within certain minimum and maximum limits. The minimum limit equals weevils present the previous week minus expected mortality plus emergence being completed during current week (second week) of a 2-week emergence period. The maximum limit equals minimum limit plus emergence expected during current week (first week) and following week (second week) of next 2-week emergence period. Net migration is indicated when the population present is not within expected limits. Weevils present minus maximum expected limit equals migrants to area, or minimum expected limit minus weevils present equals migrants from area.