Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2007
Publication Date: 2/1/2008
Citation: Vogt, J. T., Wallet, B., Freeland, T. B. Imported fire ant (Hymenoptera: Formicidae) mound shape characteristics along a north-south gradient. Environmental Entomology 37: 198-205. 2008.
Interpretive Summary: Researchers with the USDA, ARS in Stoneville, Mississippi are developing reliable methods for detecting and counting imported fire ant mounds from the air, using remote sensing technology. Fire ant mounds were generally elongated when viewed from above. Mounds were tallest and steepest when the sun was low in the sky (winter), temperatures were high enough for ant activity, and rainfall was not excessive. These findings show that remote sensing efforts for fire ant mound detection should take place during winter or early spring months unless temperatures and rainfall over the previous week to month have been unfavorable for mound-building activity.
Technical Abstract: Imported fire ant mound shape characteristics (south facing slope angle and area, mound height, and basal elongation in the plane of the ground) were quantified in 2005 and 2006 at a number of locations from about 30° 25’ N (Long Beach, Mississippi, USA) to 35° 3’ N (Fayetteville, Tennessee, USA). Insolation (w*h/m2), maximum sun angle (sun elevation in degrees above the horizon at noon, dependent upon date and latitude), cumulative rainfall (7 d and 30 d prior to sampling), and mean ambient temperature (7 d prior to sampling) for each site*date combination were used as predictive variables to explain mound shape characteristics. Steepness of south-facing mound slopes was negatively associated with maximum sun angle at higher temperatures, with predicted values falling from about 36° at sun angle = 40° to 26° at sun angle = 70°; at lower temperatures, slope remained relatively constant at 28°. On average, mound height was negatively correlated with maximum sun angle. Rainfall had a net negative effect on mound height, but mound height increased slightly with maximum sun angle when rainfall was high. Mound elongation generally increased with increased mound building activity. Under favorable temperature conditions and average rainfall, imported fire ant mounds were tallest, most eccentric, and had the steepest south facing slopes during periods of low maximum sun angle. Observations support the hypothesis that the mound serves an important function as a solar collector. Mound shape characteristics are discussed with regard to season and their potential usefulness for remote sensing efforts.