Effectiveness of Sterile Boll Weevils (Coleoptera: Curculionidae) Against a Low-Density Population in Commercially Grown Cotton in Northcentral Mississippi

Abstract

Sterile boll weevils, Anthonomus grandis grandis Boheman, were released into six fields of commercially grown cotton (total of 28.1 ha) in Choctaw County, Miss. Three fields (total of 18.8 ha) that received no sterile weevils were used as controls. Weevils were sterilized by subjecting them to 10 krad of gamma irradiation, then immersing them in either an acetone or aqueous solution of 0.04% diflubenzuron. The weevils were suspended in an aqueous solution of 0.55% furcellaran, a gelling agent, and dispensed directly onto cotton plants by means of specially designed equipment. The population of native boll weevils present in the field during the course of this test, as estimated using three techniques, averaged 4.1 per 0.4 ha/wk. This very low population of native weevils encountered during the release period allowed a test of the hypothesis that a given number of sterile weevils will produce increasingly greater reductions in egg hatch of native populations as those populations become smaller. Egg hatch in fields where the sterile weevils were released averaged 15.2% as opposed to 94.4% in control fields, indicating that sterile weevils could effect significant reductions in egg hatch of a low-level native population in commercially grown cotton. Comparing these results with those of a previous test indicated that, although egg hatch was lower in the smaller native population, the efficiency of the sterile weevils appeared to be lower with the smaller population.