Submitted to: Applied Radiation And Isotopes
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/20/2006
Publication Date: 6/7/2006
Citation: Showler, A.T., James, W.D., Armstrong, J.S., Westbrook, J.K. 2006. An experiment using neutron activation analysis and a rare earth element to mark cotton plants and two insects that feed on them. Applied Radiation and Isotopes. 64(8):875-880. Interpretive Summary: Studies on insect movement often require markers that will not alter flight and fitness. Samarium, a rare earth element, was consumed by boll weevils and beet armyworms through labeled artificial diet or living plant material. Adult boll weevils fed labeled artificial diet and beet armyworm larvae fed labeled cotton leaves had detectable amounts of samarium, but the label was excreted within days and the larvae of both insect species did not retain samarium upon development to adulthood. Although samarium can be useful as a marker when insects are presented with a continuous pulse of the label, elements that are assimilated by the insect would be more useful if a continuous infusion of the marker cannot be provided.
Technical Abstract: Studies on insect dispersal and other behaviors can benefit from using markers that will not alter flight and fitness. Rare earth elements, such as samarium (Sm), have been used as ingested markers of some insects and detected using neutron activation analysis (NAA). In this study, Sm nitrate hexahydrate was mixed into artificial diet for boll weevils, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), at different dosages, and in water used to irrigate cotton, Gossypium hirsutum L. Sm was detected in adult boll weevils fed on the Sm-labeled diet, but not after 5 or 10 d of being switched to non-labeled diet, even if the insects were given labeled diet for as long as seven consecutive days. Introduced in irrigation water, 1% Sm (m:m) was detectable in cotton squares and leaf tissue. However, boll weevil adults fed Sm-labeled squares did not retain detectable levels of Sm, nor did boll weevil adults reared to adulthood from Sm-labeled squares. Fourth instar beet armyworms, Spodoptera exigua (Hubner) (Noctuidae: Lepidoptera), fed on Sm-labeled cotton leaves obtained enough Sm for NAA detection, but adult moths reared from the larvae did not have detectable amounts of Sm. Although Sm can be useful as a marker when insects are presented with a continuous pulse of the label, elements that are assimilated by the insect would be more useful if a continuous infusion of the marker cannot be provided.