Submitted to: Journal of Radioanalytical and Nuclear Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 13, 2006
Publication Date: September 28, 2006
Citation: James, W.D., Showler, A.T., Westbrook, J.K., Armstrong, J.S. 2006. Stable isotope tracer marking of individual boll weevils. Journal of Radioanalytical and Nuclear Chemistry. 269(2):267-270. Interpretive Summary: A sensitive and durable method is needed for marking adult boll weevils to study their dispersal. Weevils were marked using the rare earth element samarium mixed at various dosages in artificial weevil diet. Samarium was readily detected, using neutron activation analysis, in weevils that consumed the diet. Marking weevils using samarium-laced diets represents a new tool for determining the extent and impact of weevil dispersal on weevil eradication programs.
Technical Abstract: Stable isotope markers have been used to study animal nutrition for several decades and more recently to study the foraging and cultural habits of imported fire ants. In this work, we have extended that effort to evaluate the potential for marking boll weevils with the rare earth element samarium. Successful marking and subsequent detection and identification of individual insects would be useful in studies of insect invasion and pest eradication protocols. Boll weevil diets labeled at dosages of 0.01%, 0.1%, and 1% samarium by weight were fed to groups of insects for a period of either 2 or 7 days. The insects were then sacrificed immediately, after 5 days, or after 10 days to evaluate the uptake and persistence of the marker in the insect body. In order to evaluate the effectiveness of marking insects by ingestion of cotton plant material, groups of weevils were fed from plants irrigated with samarium at 0.01%, 0.1%, and 1.0% aqueous samarium solutions. Neutron activation analysis was performed on the boll weevils as well as plant material from the cotton squares on which the insects were fed. Samarium levels in non-dosed insects average about 20 ng/g or about 100 pg samarium per insect. Our computed average determination limit was 36 pg Sm/weevil. The determination limit for cotton plant squares and leaves averaged 3.5ng/g and 8.2 ng/g, respectively. These initial results indicate the NAA method is capable of identifying individual marked insects which have assimilated 1ng samarium, a ten-fold increase in content over average blank values.