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Title: BOLL WEEVIL (COLEOPTERA: CURCULIONIDAE) BAIT STICKS: TOXICITY AND MALATHION CONTENT

Author
item Villavaso, Eric
item MULROONEY, JOSEPH - USDA FOREST SERVICE, MSU
item McGovern, William

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2002
Publication Date: 4/20/2003
Citation: VILLAVASO, E.J.,MULROONEY,J.E.,MCGOVERN,W.L.BOLL WEEVIL (COLEOPTERA: CURCULIONIDAE) BAIT STICKS:TOXICITY AND MALATHION CONTENT. JOURNAL OF ECONOMIC ENTOMOLOGY. 2003. v96.p.311-321.

Interpretive Summary: The boll weevil bait stick, now marketed as Boll Weevil Attract and Control Tubes(BWACT) is a unique device patented by ARS scientists. Tubes are 1.2" in outside diameter by 36" long. They have a greenish, malathion-laced coating, and a boll weevil attractant is placed in the top of each tube. BWACT work best on weevils emerging early in the cotton growing season prior to budding of cotton plants, and again as plants begin to age prior to and during boll opening. The toxicity of BWACT has been erratic, and the only way to get reliable measure of toxicity was to expose live weevils to BWACT for selected time periods. The use of live weevils is difficult because only one laboratory now rears them, and the process of exposing weevils to BWACT is tedious and time-consuming. Additionally, the efficacy of the procedure has been questioned. In our study we combined a chemical assay of malathion amounts contained on the surface of the BWACT with mortality of boll weevils exposed to the same BWACT and found a high correlation between the methods. Now the relatively simple chemical test can be used to estimate the efficacy of BWACT with no need for live weevils or the time consuming toxicity-measuring procedure. We also found that there was a direct correlation between the amount of time a weevil remained on a BWACT and the amount of malathion that adhered to the weevil, and that specific amounts of malathion would cause predictable amounts of mortality. Our live weevil essay, though tedious and time consuming was indeed a good measure of the efficacy of BWACT, but now we have a simpler one.

Technical Abstract: Biological and chemical assays were conducted on boll weevils (Anthonomus grandis grandis Boheman) exposed to bait sticks, now marketed as Boll Weevil Attract and Control Tubes(BWACT). In general, the longer BWACT were in the field, the lower the mortality of weevils exposed to bait sticks. Hexane washes of BWACT surfaces showed that mortality was correlated with surface malathion. More than 90% of weevils died when exposed to BWACT from which >34.3 ng of malathion per u1 hexane was removed by surface washes. While mortality was related to surface amounts of malathion, it was unrelated to the total amount of malathion present in BWACT. Similarly, surface malathion was unrelated to the total amount present in BWACT. As with mortality, surface malathion declined with time; total malathion did not decline with time. Boll weevils placed on fresh BWACT tended to accumulate more malathion and die in greater numbers as time spent on fresh tubes increased, but not as time spent on tubes aged in the field for five months increased. Weevils that landed on tubes after a short flight died in about the same numbers as those that were placed on tubes using a carefully-defined methodology. The amount of malathion expected to cause 90% mortality of boll weevils subjected to properly conducted methodology was 47% higher than for a less stringent methodology (34.3 ng versus 23.4 ng) which clearly demonstrates the need for strictly adhering to proper methodology for the bioassay.