Between 1982 and 1984, the Nicaraguan Ministry of Agricultural Development and Agrarian Reform (MIDINRA) used an area-wide network of trap crops of cotton from February to August to suppress boll weevils ( Anthonomus grandis Boheman) on 17450 ha (1982–1983) and 35 200 ha (1983–1984) of cotton land in the Leon region of Nicaragua. In the 1982–1983 season the programme reduced boll weevil infestations (expressed as weevil-days) 89% in Zone II (normal rainfall area) when compared with untreated controls. This suppression of adult weevils resulted in a reduction from 18 to 10 seasonal applications of methyl parathion for weevil control. The programme reduced weevil insecticide costs per kg of raw cotton produced by an area-wide average of 43%. In the 1983–1984 season the programme reduced weevil-days by an area-wide 36% in commercial fields. In Zone II, trap cropping reduced by 40% the quantity of insecticides applied for weevil control. Weevil control costs per kg of raw cotton produced were reduced by 44%. Non-significant cost reductions for weevil control in Zone I may have been due to early drought, cattle grazing on trap crop areas, or inadequate management of trap crops. The 2-year programme was the largest mobilization of public and private resources for pest management ever undertaken in Nicaragua, and gives practical evidence that suppression of between-season boll weevil populations can form the basis for more profitable control of this key pest in the commercial cotton season.