Delineating ant food webs: Overcoming PCR Inhibition

Ants (Hymenoptera: Formicidae) present ample opportunity to investigate food webs and potential biological control as they are abundant yet understudied in U.S. agricultural systems. Molecular gut-content analysis provides a way to delineate the food web linkages of ant species to their prey items based on prey DNA presence within ant guts. Though this method can provide targeted insights into prey items, ants have previously seen limited use of this method due to PCR-inhibition. When delineating food webs, any falsely negative samples due to inhibition underestimates the linkages of the food web in question and wastes both samples and reagents. This study determines which ant organs are responsible for gut-content PCR-inhibition, the variation among three species (Tetramorium caespitum, Solenopsis invicta, and Camponotus floridanus), and how to efficiently prevent this from occurring.  Although the literature has postulated that this inhibition is coming from the poison gland, we found that the gut including the crop causes significant rates of PCR-inhibition. No other organs caused significant rates of inhibition. We also found differences in the rates of PCR-inhibition among the three species tested, with T. caespitum having the greatest rates of inhibition and S. invicta having the least. However, in all species tested, enough samples exhibited PCR-inhibition to make predation data based on these samples underestimated. The most effective way we found to overcome this inhibition was to exude the crop contents onto UV-sterilized Kim Wipes without any portion of the ant gut present and extract the DNA directly from the Kim Wipe. The use of this method will provide an easy way to circumvent gut-content PCR-inhibition within ants, allowing for more detailed studies of ant food and potential for use as biological control agents in the temperate United States.