Abstract
House flies, Musca domestica L., serve as an important mechanical vector of human and veterinary pathogens, and their activity as nuisance pests likely contributes to the loss of billions of dollars annually attributed to filth flies to the U.S. agricultural industry. Synanthropic house flies are frequently exposed to microbially rich environments, as they feed and develop in human-generated organic refuse and animal excreta. Additionally, their dispersal and landing patterns are characteristics conducive to the mechanical spread of a variety of known pathogens to livestock and poultry, as well as humans. In 2021, the U.S. food-industry distributed over 11 million kg of antibiotics to treat subsequent veterinary ailments. Tetracycline and penicillin represented the largest share of medically important antibiotics distributed in the U.S., accounting for 65 and 10% of the total use, respectively. Ionophore class antibiotics accounted for 82% of the total use of those designated as medically unimportant by the Food and Drug Administration, as their use is confined to treating veterinary diseases. Although house fly reduction strategies may include several methods such as biological- and cultural control, trapping, and monitoring as part of an integrated pest management program for house flies, chemical insecticides remain central to mitigating their populations. Pyrethroid and neonicotinoid class insecticides are the most used worldwide, but the use of newer insecticide classes such as the ryanoids is rising due to benefits that include lower mammalian toxicity. However, house flies often exhibit resistance to new insecticide formulations as quickly as they are developed. House flies are known to evolve target site insensitivity and increased metabolic detoxification mechanisms to overcome insecticide exposure, which is fostered by their short generation period. While resistance evolution due to traditional insecticide use in field populations has been largely observed, less is known about the off-target effects of other xenobiotics such as antibiotics on this phenomenon in adult house flies. Therefore, a study was conducted to ascertain the effects of antibiotic exposure on insecticide susceptibility in the house fly. Overall, antibiotic exposure caused significant increases in susceptibility in a field-collected house fly strain. The following outlines a study conducted to elucidate the effects that tetracycline and amoxicillin exposure in adult house flies exhibited on the efficacy of two commonly-used commercial insecticidal scatter baits, QuickBayt® and Cyanarox®.