Lado, P. | bioRxiv Science

bioRxiv2025

Evaluation of the safety and insecticidal efficacy of ivermectin-treated bird feed formulations in different avian species

BackgroundWest Nile virus (WNV) is maintained in an enzootic cycle between reservoir host birds and Culex (Cx.) spp. mosquitoes. This relationship presents a potential target for vector control strategies. Ivermectin (IVM), an endectocidal drug that selectively affects invertebrates while remaining safe at high concentrations in mammals and birds, can be delivered to Cx. tarsalis via blood meals from birds fed IVM-treated bird feed. In this study we evaluated the safety, efficacy, and utility of IVM-treated bird feed as a novel vector control strategy by assessing its impact on multiple bird species and mosquitoes. MethodsMosquitoes were collected during peak WNV transmission season in Northern Colorado and DNA extracted from blood meals to determine host species. Chickens, pigeons, zebra finches, and house sparrows were fed different formulations of IVM-treated bird feed and observed for clinical signs, and their sera were fed to Cx. tarsalis mosquitoes to evaluate mosquitocidal efficacy. Feeding rates and IVM serum concentrations in birds were analyzed by unpaired t-test and one-way ANOVA, and mosquito survivorship was analyzed by Kaplan-Meier curves and compared using paired log-rank tests. IVM serum concentration and mosquito survivorship were compared using Spearman correlation. ResultsSpeciation analyses conducted on blood meals from Cx. tarsalis collected during peak WNV transmission season in Northern Colorado determined that they feed primarily on songbird species that commonly visit bird feeders, with house sparrows representing the most frequent blood meal host. In laboratory experiments using multiple formulations and doses of IVM, chickens, pigeons, zebra finches, and house sparrows ate comparable amounts of IVM-treated bird feed compared to untreated feed, had similar weight gain, and exhibited no clinical signs of toxicity. Both colony-reared and locally captured Cx. tarsalis showed significant mortality after feeding on sera from IVM-treated birds compared to controls. ConclusionsThese results suggest that targeting songbirds with IVM-treated bird feed should be safe for wildlife and may elicit high rates of IVM-induced mortality by reaching a large proportion of WNV vector mosquitoes via their proclivity for feeding on passerine birds.

microbiology↗

bioRxiv2023

The microbiota of Amblyomma americanum reflects known westward expansion.

AbstractAmblyomma americanum, a known vector of multiple tick-borne pathogens, has expanded its geographic distribution across the United States in the past decades. Tick microbiomes may play a role shaping their hosts life history and vectorial capacity. Bacterial communities associated with A. americanum may reflect, or enable, geographic expansion and studying the microbiota will improve understanding of tick- borne disease ecology. We examined the microbiota structure of 189 adult ticks collected in four regions encompassing their historical and current geographic distribution. Both geographic region of origin and sex were significant predictors of alpha diversity. As in other tick models, within-sample diversity was low and uneven given the presence of dominant endosymbionts. Beta diversity analyses revealed that bacterial profiles of ticks of both sexes collected in the West were significantly different from those of the Historic range. Biomarkers were identified for all regions except the historical range. In addition, Bray-Curtis dissimilarities overall increased with distance between sites. Relative quantification of ecological processes showed that, for females and males, respectively, drift and dispersal limitation were the primary drivers of community assembly. Collectively, our findings highlight how microbiota structural variance discriminates the western-expanded populations of A. americanum ticks from the Historical range. Spatial autocorrelation, and particularly the detection of non- selective ecological processes, are indicative of geographic isolation. Our conclusions demonstrate the value of synergistic analysis of biogeographic and microbial ecology data in investigating range expansion in A. americanum and potentially other tick vectors as well. ImportanceThe incidence of tick-borne diseases is on the rise worldwide, including in the United States. This increase in cases is in large part due to the geographic expansion of tick vectors. Among them is the Lone Star tick, Amblyomma americanum, and understanding the factors driving its recent expansion is important for risk assessment and tick population control. Climate change and human activities have previously been posited to be main driving forces for their expansion. New sources of relevant biological data can further our understanding of this phenomenon. Microbial communities associated with ticks include bacteria that affect pathogen transmission and tick behaviors. Here, we investigated whether bacterial community and geographic location data could be combined to better understand the expansion of A. americanum populations. Its not clear whether differences in the microbiota are reflective of or facilitating expansion, but our findings suggest this approach is promising and warrants further investigation.

ecology↗