Biological Control of Larrea Tridentata: Insect Fauna Survey
Schramke, Mary L.
MetadataShow full item record
Larrea tridentata is a prolific rangeland weed that has a significant detrimental impact on the economic value of the grazing lands of the southwestern United States. This report identifies and quantifies the insect community of Larrea tridentata in western Texas from June to September, 1977. Insect populations were sampled from dense stands of Larrea tridentata. Of the 11 insect families collected from L. tridentata, only three families were present throughout the study: Membracidae, Formicidae and Geometridae. Larvae of the moth Semiothisa colorata were collected from L. tridentata and reared in the laboratory to characterize the moth's life history and food preference, in order to evaluate the potential for using S. colorata as an agent to biologically control Larrea species. Females of the moth laid an average of 5.9 eggs per day. Oviposition on the upper leaf surfaces of L.tridentata occurred significantly more frequently (p<O.005) than oviposition on stems and lower leaf surfaces. Eggs required 2 to 3 days to hatch, the 5 larval instars took 12 to 15 days to pupate and pupae took 6 to 7 days to emerge. In the laboratory, 56.4% of the eggs survived to hatching, 64.2% of the larvae pupated and 94.3% of the pupae emerged as adults. Parasitism plagued 15 out of 55 larvae (27%) collected from various sites within the study area. Vegetation analysis found Larrea tridentata in association with Flourensia cernua and Gutierezzia lucida. Vegetation accounted for 14.6% of the total ground cover. Larrea tridentata had a greater percent relative dominance than other vegetation (p<O.02).Insect community analysis is compared with results of arthropod community studies by Schultz of Larrea species in both North and South America.