Modelling the Interaction of Cotton and the Cotton Boll Weevil. II. Bollweevil (Anthonomus grandis) in Brazil

(1) A population dynamics model of the field biology of the cotton boll weevil (Anthonomus grandis Boh.) under Brazilian conditions was linked to a model for cotton growth and development. An age-structured, distributed maturation times population dynamics model with attrition was used for both the plant and the weevil. The models are demand driven, and all aspects of the biology are controlled by the interplay of resource supply and demand. The model compared quite favourably to field data. (2) The compounding effects of low soil nitrogen on both plant and weevil dynamics were examined. (3) The biology of the weevil in Brazil is similar to that reported for its North American relative, except that it readily attacks bolls. Fire ants (Solenopsis spp.) appear to be an important predator of boll weevil immatures. (4) The fruiting dynamics of the plant were shown to affect greatly the dynamics of the weevil, and vice-versa. (5) Simulation analysis suggests that IAC cottons that are currently the mainstay of the industry in Brazil are poorly suited to compensate for boll weevil damage. The model suggests that short season cottons similar to those developed in North America might be suitable alternatives. An explanation is given in terms of per fruit losses and fruit bud replacement rates. (6) The simulation analysis shows that insecticides are needed to control this pest as effective biological control agents are absent in Brazil. The model suggests that the use of an economic threshold based on the ratio of the rate of fruit point production to fruit damage can greatly reduce the number of applications required. Increasing the per unit cost of insecticides on their use was explored.