The boll weevil, Anthonomus grandis grandis (Boheman), is a major pest of cotton (Gossypium hirsutum L.), and responsible for an estimated $300 million in annual losses (National Cotton Council of America 2009, Texas Boll Weevil Eradication Foundation, Inc. 2009). Current boll weevil eradication programs depend on malathion ULV to achieve and maintain eradication status. Should this effective and economical insecticide become unavailable, eradication efforts could be jeopardized. The objective of this project was to evaluate the efficacy of selected insecticides as alternatives to malathion ULV on field collected boll weevils. The study was conducted in the Lower Rio Grande Valley of Texas in 2007. Insecticides included malathion ULV, endosulfan, bifenthrin, encapsulated methyl parathion, oxamyl, carbaryl and cyfluthrin. Malathion ULV was applied using an ULV, controlled-droplet applicator. Other insecticides were applied with a hand-held, CO2-charged sprayer. Leaf disks were removed from treated cotton, placed in culture plates and infested with individual adult boll weevils. Boll weevil mortality in the malathion ULV, endosulfan, encapsulated methyl parathion and bifenthrin treatments was at or near 100%. Mortality with cyfluthrin and carbaryl was low and inconsistent. Mortality in the oxamyl treatment was intermediate between the two above groups. Highest mortality after 24 h was observed with malathion ULV (97.9%), endosulfan (86.6%) and bifenthrin (80.2%). After 48 h, mortality reached 100% with malathion ULV but was not significantly different from those of encapsulated methyl parathion (96.1%), bifenthrin (95%) and endosulfan (94.9%). Results indicate that malathion ULV is a highly effective material for boll weevil control and that encapsulated methyl parathion, bifenthrin and endosulfan also cause high mortality.
