Bacterial symbionts of Reticulitermes flavipes have inherent pesticide tolerance

Reticulitermes flavipes, the eastern subterranean termite, is an important structural pest in the United States. The primary means to control termites in urban and suburban areas are bait traps, soil drenches, and sprays containing the imidacloprid as the active ingredient.  Imidacloprid has insecticidal activity both topically and orally, but the slow-acting baits used for colony eradication are designed to be consumed and transferred by termite workers. Termites are well-known for their intimate and obligate association with gut symbionts that have impact host digestion, immunity, development, and other physiologies. Recently, insecticide failure has been linked to symbiont-mediated detoxification of pesticides in a myriad of insect hosts including other members of Blattodea. Given the close association and interdependence of termites and their gut microbiota, we wanted to investigate the potential for a bacteria-derived mechanism for imidacloprid degradation. Interesting, imidacloprid is known to cause perturbation in the termite gut protist community but had limit impact on the abundance of bacteria. We hypothesized that bacteria from the termite gut are inherently tolerant to imidacloprid. To test this hypothesis, we screened twenty-two bacterial isolates from the termite gut for innate imidacloprid tolerance in liquid growth assay, subjected tolerant isolates to continuous culture in insecticide rich medium, and measures protein and enzyme activity of these isolates grown at a range of pesticide concentrations. Taken together, these findings support a novel concept that even susceptible insect hosts harbor pesticide tolerant symbionts. Additionally, insect symbionts represent a source of insecticide bioremediation potential that remains untapped.