Abstract
The German cockroach (Blattella germanica L.) is a major urban pest worldwide and is known for its ability to resist insecticides. Past research has shown that gut bacteria in other insects can metabolize xenobiotics, allowing the host to develop resistance. The research presented here determined differences in gut microbial composition between insecticide-resistant and susceptible German cockroaches and compared microbiome changes with antibiotic treatment. Cockroaches received either control diet or diet plus kanamycin (KAN) to quantify shifts in microbial composition. Additionally, both resistant and susceptible strains were challenged with diets containing the insecticides abamectin and fipronil in the presence and absence of antibiotic. In both strains, KAN treatment reduced feeding, leading to higher doses of abamectin and fipronil being tolerated. However, LC50 resistance ratios between resistant and susceptible strains decreased by half with KAN treatment, suggesting gut bacteria mediate resistance. Next, whole guts were isolated, bacterial DNA extracted, and 16S MiSeq was performed. Unlike most bacterial taxa, Stenotrophomonas increased in abundance in only the kanamycin-treated resistant strain and was the most indicative genus in classifying between control and kanamycin-treated cockroach guts. These findings provide unique insights into how the gut microbiome responds to stress and disturbance, and important new insights into microbiome-mediated insecticide resistance.
Highlights
Abbreviations DAN Danville, IL Resistant strain J-WAX S.C
Resistance ratios between the resistant and susceptible strains decreased by approximately half with KAN treatment, suggesting potential roles for gut bacteria in mediating resistance
We found that pre-treatment with the antimicrobial compound kanamycin (KAN) led to reductions in resistance levels and increased basal toxicity levels in both resistant and susceptible strains tested. 16S bacterial sequence surveys revealed a wide variety of undescribed bacterial taxa, and both strains were more similar before KAN treatment than after, with a stronger dysbiosis effect in the resistant strain
Summary
Abbreviations DAN Danville, IL Resistant strain J-WAX S.C. Johnson Wax Susceptible strain CTRL Control treatment KAN Kanamycin/kanamycin treatment OTU Operational taxonomic unit. If the same insecticide is consistently applied to the same insect population in the same geographic location, within a small number of generations the majority of the population will express genetic resistance to the specific insecticide This cycle significantly reduces the lethality of insecticides with each subsequent generation of insecticide-resistant pests. German cockroaches pose a hazard to human health and well-being by carrying pathogens and pathogenic organisms, instigating allergic reactions and scattering fecal matter and carcasses throughout r esidences[7,11] It prefers foods rich in carbohydrate compared to foods rich in fat and protein content[12], the German cockroach will eat virtually any type of food substance it e ncounters[13], allowing it to adapt to unkempt areas such as kitchens, bathrooms and pantries. German cockroaches forage at random and cannot detect food or water more than a few centimeters away[14], forcing German cockroach colonies to spread out and colonize new areas quickly
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