Biological Control of Astragalus: An Insect Survey
Latta, Jill Meredith
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Astragalus millissimus (Woolly Locoweed) and Astragalus wootoni (Garboncillo) are rangeland weeds which cause significant economic losses in west Texas. Their toxic nature is responsible for substantial damage by poisoning livestock. This report identifies and quantifies the insect populations which feed on Astragalus in order to identify those which might be effective in a biological control program. Insect populations were sampled at three locations of A. mollissirnus and one location of A. wootoni in west Texas from January to mid-March, 1980. For both species, Cicadellidae, Aphididae and Lepidoptera larvae were the most abundant insect populations found on the foliage. In A. mollissimus, Walshia miscecolorella, Hylemya lupini and Curculionidae larvae were found to be the most abundant and causing the most damage to the stems, roots and leaf petioles. In A. wootoni, Curculionidae larvae and eggs were in the highest concentrations. Plant size (crown width, height and stem diameter) , density and seasonal growth were also determined. The density of A. wootoni was not measured due to the patchiness of its distribution. The density of A. mollissimus varied from 110 to 46 plants/50 m2. The size of the insect populations did not appear to be related to density or size of the plants. Seasonal growth patterns suggested that the root and stern boring larvae were keeping the A. mollissimus but not A. wootoni plants from increasing in crown width and height. Larvae and pupae of Hylemya lupini were collected in the field and reared in the laboratory in an attempt to characterize this fly's life history and evaluate its potential as a biological control agent. The laboratory pupal stage lasted 9 to 17 days (mean = 15 days). No eggs were laid.