Influence of abiotic factors on red imported fire ant (Hymenoptera: Formicidae) mound population ratings in Louisiana

Colony size and reproductive status of Solenopsis invicta (Buren), red imported fire ants, is measured by a rating system developed by Harlan et al. (1981). Because this rating system is commonly used to evaluate chemical controls, especially insect growth regulators, and biological controls such as Thelohania spp., we evaluated the environmental conditions that would affect mound ratings in Louisiana. Increases in relative humidity arid mound height were associated with population rating increases. Brood presence in the above ground portion of the nest (mound) was strongly associated with mound temperature. Brood was only found in mounds that had soil temperatures between 25-30degreesC although mound temperatures may fall below 25degreesC in the early morning arid reached 40degreesC by early afternoon during the summer in Louisiana. Researchers in warm climates such as Louisiana may consider monitoring mound temperature during sampling and excavating nests below ground surface to ensure that assessments of mound ratings are accurate.