We report the susceptibility of a green plant bug, Creontiades signatus Distant, a pest of cotton, Gossypium hirsutum L., and other crops in South Texas, to malathion and other cotton insecticides using the adult vial test, and an oral “floral foam” assay for systemic insecticides, when active eradication of boll weevil, Anthonomus grandis grandis Boheman, has been in effect for six seasons in the Rio Grande Valley of Texas. Field-collected green plant bugs exhibited malathion tolerance ratios of 1.68 to 4.83 when compared to unexposed plant bugs reared in the laboratory for six generations. The associated 95% C.l.'s for LC₅₀ values did not overlap following six consecutive paired (field versus laboratory) assays from November 2006 to October 2009. The greater tolerance ratios and LC₅₀ values may be the result of an average of 18 to 20 applications of ultra-low volume (ULV) malathion applied in the process of boll weevil eradication in cotton fields. Field-collected green plant bugs also had larger LC₅₀ values when exposed to acephate using an adult vial test compared to the laboratory strain, but the 95% C.l.s did not overlap. All other organophosphate, pyrethroid, carbamate, neonicotinoid, and flonicomid insecticides were very toxic against field- and laboratory-reared green plant bugs. The floral foam method of diluting non-acetone soluble insecticide active ingredients into honey-water worked well as an assay technique with the exception that mortality should be observed at 72 instead of 48 hours.