1. Evaluation of Mechanical Disturbance of Mounds During Cold Weather on Red Imported Fire Ants Lawrence C. ‘Fudd’ Graham 1, Vicky E. Bertagnolli 1, and Amber T. Kelley 2 1 Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849-5413 2 Department of Entomology and Plant Pathology, Mississippi State University, Starkville, MS 39762-9775 Introduction Control of red imported fire ants, Solenopsis invicta, using baits or contact insecticides is cost prohibitive in many agricultural settings such as pastures. Shallow disking of a pasture or dragging heavy objects across the pasture are recommended nonchemical management strategies (Drees et. al., 2002). Mechanical control during mild weather conditions usually serves to temporarily flatten hardened mounds and some workers may be damaged. However, disturbing mounds during drought or cold weather may reduce populations by exposing the ants to adverse weather conditions. The purpose of this study was to evaluate the effect of mechanical disturbance of mounds during cold weather on red imported fire ant populations. Methods and Materials Three treatments were replicated four times in a randomized complete block design. The twelve plots were arranged in a 3.24 ha hay field. Plot size varied within the field to allow for approximately equal numbers of mounds within each plot. Initial treatments were: 1) {cold} mound disturbance just before a cold front; 2) {warm} mound disturbance during average winter weather; and 3) an undisturbed control. A cold front was defined as a weather system predicted to have several nights below freezing with daily temperatures remaining below 10  C. Average weather was defined as weather with temperatures above 10  C and nights near freezing. Plots were established and pretreatment population data were collected on October 23, 2001. Mounds were flagged, counted, and rated small ( 10,000) based on the number of workers present (Lofgren and Williams, 1982). A garden rake was used to simulate dragging in the cold and warm treatment plots. Mounds in the warm treatment were disturbed on December 24, 2001 when the daily high was 20  C and the overnight low was -1  C. Mounds in the cold treatment were disturbed on December 26. The daily high was 7.8  C and the overnight low was -5.5  C. Night time temperatures remained at freezing or below until January 11, 2002. Data were analyzed using the PROC GLM (SAS Institute, 1989b) and means were separated using LSD procedures. References Drees, B. M., C. L. Barr, D. R. Shanklin, D. K. Pollet, K. L. Flanders and B. Sparks. 1999. Managing red imported fire ants in agriculture. Texas A & M Extension Service Bulletin, B-6076. Lofgren, C. F. and D. F. Williams. 1982. Avermectin B 1 a: Highly potent inhibitor of reproduction by queens of the red imported fire ant (Hymenoptera: Formicidae). J. Econ. Entomol. 75 :798-803. SAS Institute Inc. 1989b. SAS/STAT® Users Guide, Version 6, Fourth Edition, Volume 2, SAS Institute Inc., Cary, NC. Results Fig. 1. In all treatments, total mound numbers were higher in April than in October. However, the number of large mounds decreased slightly in the cold treatment and increased in the undisturbed control. Fig. 2. Numbers of large mounds remained approximately the same pre- and posttreatment in both the warm and cold treatments while numbers of small and medium size mounds tended to increase slightly. This increase in small and medium mounds accounts for the increase in total mounds posttreatment in both treatments. In the untreated control, medium size mound numbers decreased slightly while numbers of large mounds increased, suggesting that the medium size mounds matured during the spring and developed into large mounds. Fig. 3. There was a significant difference in the percent change in numbers of large mounds between treatments. The percentage of large mounds decreased in the cold treatment while the percentage of large mounds increased significantly in the untreated control. Since no differences were found between mound numbers in the warm and cold treatments, data were pooled. There were significantly more mounds postreatment in the control than in the disturbed treatments. a ab b a b While total mound numbers were not significantly affected by the treatments, the number of large mounds decreased in response to the disturbance during cold weather. This method of control will reduce fire ant numbers somewhat, but several disturbances during the winter could possibly increase mortality further. This control method could improve the effectiveness of a planned baiting program in the spring.