The boll weevil, Anthonomus grandis Boh., first exhibited resistance to the chlorinated hydrocarbon insecticides in 1955. Delineation of the area infested with resistant boll weevils was undertaken in 1956. Collections or infested cotton squares (flower buds) were made throughout the suspected area, brought into the laboratory, and held until adults emerged. Dosage-mortality curves were established for each collection and compared to a known susceptible culture. Boundaries of areas infested with resistant boll weevils were established, and control recommendations for these areas made accordingly.

Current studies show that a degree or reversion to susceptibility is occurring in field populations. There appears to be no change in response of the boll weevil to the organo-phosphorus insecticide after 4 years or extensive applications.