Efficacy of the InvictDetectTM Immunostrip® to taxonomically identify the red imported fire ant, Solenopsis invicta using a single worker ant

Authors: Valles, Steven; Strong, Charles; EMMITT, ROBERT - Agdia; CULKIN, CHRIS - Agdia; WEEKS, RONALD - US Department Of Agriculture (USDA)

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2019
Publication Date: 1/1/2020
Citation: Valles, S.M., Strong, C.A., Emmitt, R., Culkin, C., Weeks, R.D. 2020. Efficacy of the InvictDetectTM Immunostrip® to taxonomically identify the red imported fire ant, Solenopsis invicta using a single worker ant. Insects. 11(1):37. https://doi.org/10.3390/insects11010037.
DOI: https://doi.org/10.3390/insects11010037

Interpretive Summary: The red imported fire ant is a highly invasive species that was introduced into the United States in the 1930s. The ant causes approximately US$6 billion in damage annually to livestock and agricultural production and poses a serious threat to human health. Field detection of the ant is crucial to prevent its spread beyond the quarantined area in the U.S. and at ports of entry around the world. Scientists at the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL), USDA-APHIS (Raleigh, NC), and Agdia, Inc. have developed a lateral flow immunoassay that provides a rapid and portable method for the identification of Solenopsis invicta imported fire ants. The test was evaluated in Florida under field conditions to determine its efficacy using a single worker ant for identification. Under these conditions, the test provides a 75% chance of positive identification. Thus, it is recommended that a minimum of 3 worker ants be used to achieve a 99% detection rate.

Technical Abstract: Early detection and identification are crucial to intercepting the red imported fire ant Solenopsis invicta and preventing it from becoming established in new areas. Unfortunately, visual identification of fire ants, including S. invicta, to species is difficult, and ant samples often must be couriered to an expert for positive identification, which can delay control interventions. In response to this need, a lateral flow immunoassay that provides a rapid and portable method for the identification of S. invicta ants was developed and commercialized, and is available from Agdia, Inc. under the Trade name InvictDetectTM. The test requires a minimum sample of three ant workers, which has been criticized recently, so we field tested InvictDetectTM Immunostrips® against homogenates prepared from single S. invicta workers to determine the effectiveness of the method under these conditions. The false negative response rate observed in the field for monogyne and polygyne individual workers was 21.1% and 38.9%, respectively. The false negative response rate was decreased to 5.8% (monogyne) and 22.2% (polygyne) when a repeat test was performed, again using a single ant worker. Disregarding the social form, the false negative rate was 25.5% for the initial single worker ant test, and 10% after a repeat test was performed. So, when two individual ant workers from a colony were interrogated separately with InvictDetectTM Immunostrips®, positive identification was 90%. Because S. invicta is a polymorphic species we were curious to know if the InvictDetectTM false negative responses when using a single worker ant were related to the mass/size of the ant worker. Tests indicated that InvictDetectTM false negative response was independent of worker weight. Although InvictDetectTM requires a minimum of three worker ants, the test can be conducted in the field, is completed in 10 to 30 minutes, and requires no special training or expertise.