Baseline susceptibility of Creontiades signatus to cotton insecticides, with emphasis on malathion

Authors: Armstrong, John; Coleman, Randy; Adamczyk, John

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2011
Publication Date: 6/1/2011
Citation: Armstrong, J.S., Coleman, R.J., Adamczyk Jr, J.J. 2011. Baseline susceptibility of Creontiades signatus to cotton insecticides, with emphasis on malathion. Southwestern Entomologist. 36(2):145-153.

Interpretive Summary: We determined the baseline susceptibility of a relatively new plant bug pest of cotton, Creontiades signatus (Distant), to several commonly used cotton insecticides using the traditional adult vial test (AVT) for older chemistry (pyrethroids, carbamates and organophosphates), where the active ingredient is coated inside glass vials, and a novel method of exposing the plant bug to the relatively newer insecticide chemistry (neonicitinoids). The active ingredients of the newer insecticides are not soluble in acetone, so they were diluted in honey-water and injected into floral foam where the plant bugs ingested the toxicants. The emphasis of the study was on the mortality curves and lethal dose values for malathion, an organophosphate used for eradicating the boll weevil from all cotton growing regions in the United Sates. Malathion lethal dose values were slightly elevated up to 5 times for field-collected plant bugs when compared against non-exposed laboratory individuals, and this was during the active cotton growing season when several malathion applications are being made for boll weevil eradication. All other organophosphate, pyrethroid, and carbamate insecticides, as well as the neonicotinoids and the pyridinecarboxamide (flonicomid) tested showed good activity against field and laboratory reared green plant bugs. The floral foam method of diluting non-acetone soluble insecticide active ingredients into honey-water worked very well as an assay technique with the exception that mortality should be observed at 72 h instead of 48.

Technical Abstract: We report, for the first time, the susceptibility of a green plant bug, Creontiades signatus Distant, a pest of cotton and other crops in south Texas, to malathion and other cotton insecticides using the adult vial test (AVT), and an oral “floral foam” assay for systemic insecticides, as active boll weevil eradication proceeds to it’s 5th season in the Rio Grande Valley of Texas. Field collected green plant bugs exhibited malathion resistance ratios of 1.68 to 4.83 when compared to green plant bugs reared in the laboratory, and the associated 95% confidence intervals for LC50 values did not overlap following 6 consecutive paired (field vs. laboratory) assays conducted from November 2006 to October 2009. The higher resistance ratios and LC values may be the result of an average of 18 to 20 applications of ultra-low volume (ULV) malathion being applied to cotton fields in the process of boll weevil, Anthonomus grandis grandis Bohemia eradication. Field collected green plant bugs also had higher LC50 values when exposed to acephate using the AVT compared to the laboratory strain, but the 95% C.I.’s did not overlap. All other organophosphate, pyrethroid, and carbamate insecticides, as well as the neonicotinoids and the pyridinecarboxamide (flonicomid) tested showed good activity against field and laboratory reared green plant bugs. The floral foam method of diluting non-acetone soluble insecticide active ingredients into honey-water worked very well as an assay technique with the exception that mortality should be observed at 72 h instead of 48.