THE RELATIONSHIP BETWEEN INSECTICIDE SUSCEPTIBILITY AND THE GUT MICROBIOME OF GERMAN COCKROACH (BLATTELLA GERMANICA L.)

The objectives of this dissertation included comparing the whole gut bacterial profiles of insecticide resistant and susceptible B. germanica and determining how these profiles, as well as the structure and function of the gut microbiome, change in the presence of an antibiotic. Additional goals were to investigate how antibiotic treatment impacts the toxicity of the bait insecticides fipronil, abamectin and indoxacarb, and to determine how gut bacteria, and specifically the enzymes originating within gut bacteria, metabolize and convert ingested indoxacarb into its toxic metabolite DCJW. Findings show that pre-treatment with the antimicrobial compound kanamycin (KAN) led to reductions in resistance levels for fipronil and abamectin, but also increased basal toxicity levels in both resistant and susceptible strains tested. 16S bacterial sequence surveys revealed that resistant and susceptible cockroach strains were more similar before KAN treatment than after, with a stronger dysbiosis effect in the resistant strain. For the insecticide indoxacarb, regardless of strain, roaches treated with kanamycin-infused water in feeding bioassays were more susceptible compared to the control treatment, but in vial (surface contact) bioassays, only susceptible cockroaches experienced a significant shift in mortality. When the frass of indoxacarb-fed cockroaches was analyzed, fewer molecules of the hydrolytic metabolite DCJW were produced with the introduction of an antibiotic (KAN). This result was further corroborated by esterase activity assays of whole homogenized cockroach guts. All results considered, these findings provide novel evidence of microbe-mediated pro-insecticide activation in the cockroach gut. Overall, the results of this dissertation reveal previously unknown relationships between gut microbiota and their insect hosts. These microbiome relationships exposed important cockroach strain differences which may extend to the host population level. Furthermore, this research has connected a change in enzyme activity in the gut microbiome with indoxacarb, a very important marketplace pro-insecticide.