Locoweeds, Astragalus mollissimus Torr. and Oxytropis sericea Nut., are native poisonous rangeland weeds that cause significant damage to livestock in the western United States. Locoweeds contain the indolizidine alkaloid, swainsonine, which if ingested by vertebrates, can lead to depression, abortion and death. Several native insects have been observed feeding on locoweed roots and stems. One of the most common and destructive is Cleonidius trivittatus (Say), the four-lined locoweed weevil. To determine if herbivory influences swainsonine content, several hundred mature plants at different field locations were sampled for insect damage including past, current and no damage. Additionally, to determine if swainsonine levels influence host selection seedlings of both plants were collected and grown in a greenhouse under drip irrigation. Cleonidius trivittatus were collected as eggs and larvae in plants and reared in an artificial locoweed diet to the adult stage. Adults and greenhouse grown plants were used in choice/no choice experiments. Swainsonine was extracted from plants using cation exchange chromatography and analyzed using liquid chromatography mass spectrometry. There were no significant differences in swainsonine levels between plants showing signs of past/current insect damage with those showing no signs of insect damage and preliminary results suggest that host preference is not influenced by swainsonine levels. These results will add to the knowledge of biological control as an option for managing locoweed.