Biology subjects

Black, W. C.

Publications and source records attributed to Black, W. C..

4 recordsLinked to original sources

bioRxiv2024

Discovery and characterization of chromosomal inversions in the arboviral vector mosquito Aedes aegypti

Chromosomal inversions play a fundamental role in evolution and have been shown to regulate epidemiologically important traits in malaria mosquitoes. However, they have never been characterized in Aedes aegypti, the major vector of arboviruses, because of the poor structure of its polytene chromosomes. In this study, we applied a Hi-C proximity ligation approach to identify chromosomal inversions in 25 strains of Ae. aegypti, acquired from its worldwide distribution, as well as in one strain of Ae. mascarensis. The study identified 21 multi-megabase inversions with uneven distributions along the three chromosomes. All chromosomal inversions, including one specific for Ae. mascarensis, were polymorphic. Nevertheless, geographic origin separated the strains into two clusters carrying African and non-African inversions suggesting their potential association with Ae. aegypti subspecies. Some of the inversions colocalized with chemoreceptor genes and quantitative trait loci associated with pathogen infection, implicating the potential role of inversions in host choice and disease transmission.

evolutionary biology↗

bioRxiv2023

Pyrethroid susceptibility reversal in Aedes aegypti: a longitudinal study in Tapachula, Mexico

Pyrethroid resistance in Aedes aegypti has become widespread after almost two decades of frequent applications to reduce the transmission of mosquito-borne diseases. Because few insecticide classes are available for public health use, insecticide resistance management (IRM) is proposed as a strategy to retain their use. A key hypothesis of IRM assumes that negative fitness is associated with resistance, and when insecticides are removed from use, susceptibility is restored. In Tapachula, Mexico, pyrethroids (PYRs) were used exclusively by dengue control programs for 15 years, thereby contributing to selection for high PYR resistance in mosquitoes and failure in dengue control. In 2013, PYRs were replaced by organophosphates--insecticides from a class with a different mode of action. To test the hypothesis that PYR resistance is reversed in the absence of PYRs, we monitored Ae. aegyptis PYR resistance from 2016 to 2021 in Tapachula. We observed significant declining rates in the lethal concentration 50 (LC50), for permethrin and deltamethrin. For each month following the discontinuation of PYR use by vector control programs, we observed increases in the odds of mosquitoes dying by 1.5% and 8.4% for permethrin and deltamethrin, respectively. Also, knockdown-resistance mutations (kdr) in the voltage-gated sodium channel explained the variation in the permethrin LC50s, whereas variation in the deltamethrin LC50s was only explained by time. This trend was rapidly offset by application of a mixture of neonicotinoid and PYRs by vector control programs. Our results suggest that IRM strategies can be used to reverse PYR resistance in Ae. aegypti; however, long-term commitment by operational and community programs will be required for success. Author summaryThe mosquito Aedes aegypti is the principal urban vector of the viruses that cause three globally significant diseases: dengue fever, chikungunya, and Zika fever, for which vaccines and effective treatments are currently absent. The only way to control dengue, chikungunya, and Zika fever outbreaks is to diminish vector populations. During epidemics, the most frequent way of targeting adult mosquitoes is outdoor spatial spraying of insecticides. Control of Ae. aegypti is difficult because limited insecticide classes are available for public health, leading to operational practices that overuse single molecules for long periods of time, imposing great selection pressure on mosquito populations for insecticide resistance. Insecticide resistance management (IRM) is proposed as a strategy to prevent resistance and avoid depleting the susceptibility resource in mosquito populations. IRM strategies assume that alternation of insecticides with different toxicological modes of action will prevent the selection of resistance. Unfortunately, very few field evaluations have reported IRM schemes to control Ae. aegypti. In our study, the exclusive use of pyrethroids in vector control programs in Mexico from 1999 to 2013, led in the selection of knockdown resistance (kdr) to pyrethroid insecticides. To address this issue, vector control programs temporarily phased out pyrethroids from 2013 to 2019, substituting them with an insecticide class with a different mode of action: organophosphates (OPs). During six years, we monitored pyrethroid resistance in 24 mosquito populations from Tapachula, Mexico. We show that discontinuing pyrethroids for six years led in pyrethroid resistance reversal in Ae. aegypti in the field. However, high levels of pyrethroid resistance continue to jeopardize operational application, necessitating longer periods of pyrethroid cessation and novel IRM strategies to achieve lower resistance thresholds.

evolutionary biology↗

bioRxiv2019

Loss of pyrethroid resistance in newly established laboratory colonies of Aedes aegypti

BackgroundResistance to pyrethroid insecticides in Aedes aegypti has become widespread after almost two decades of their frequent use to reduce arbovirus transmission. Despite this, use of pyrethroids continues because they are relatively inexpensive and because of their low human toxicity. Resistance management has been proposed as a means to retain the use of pyrethroids in natural populations. A key component of resistance management assumes that there is a negative fitness associated with resistance alleles so that when insecticides are removed, resistance alleles will decline in frequency. At least three studies in Ae. aegypti have demonstrated a decrease in pyrethroid resistance once the insecticide is removed.\n\nMethods/Principal FindingsThe present study aims to evaluate variation in the loss of pyrethroid resistance among newly established laboratory populations of Ae. aegypti from Mexico. Eight field collections were maintained for up to eight generations and we recorded changes in the frequencies of mutations at the V1,016I locus and at the F1,534C locus in the voltage gated sodium channel (VGSC) gene. I1,016 and C1,534 confer resistance. We also examined resistance ratios (RR) with type 1 and 2 pyrethroids.\n\nConclusions/SignificanceWe demonstrate that, in general, the frequency of the Ae. aegypti pyrethroid resistance alleles I1,016 and C1,534 decline when they are freed from pyrethroid pressure in the laboratory. However, the pattern of decline is strain dependent. In agreement with earlier studies, RR was positively correlated with I1,016 resistant allele frequencies and showed significant protection against permethrin, and deltamethrin whereas F1534C showed protection against permethrin but not against deltamethrin.\n\nAuthor SummaryThe author is interested in the evolution of genes that confer resistance to insecticides, especially when this evolution affects binding of insecticides to their target site. The Voltage Gated Sodium Channel gene represents an excellent opportunity to understand how mutations at the target site(s) affect the evolution of resistance in many different pest insect species including Aedes aegypti, the primary vector of Dengue Virus, Yellow Fever, Zika and Chikungunya arboviruses.

genetics↗

bioRxiv2018

A reverse-transcription/RNase H based protocol for depletion of mosquito ribosomal RNA facilitates viral intrahost evolution analysis, transcriptomics and pathogen discovery.

Studies aimed at identifying novel viral sequences or assessing intrahost viral variation require sufficient sequencing coverage to assemble contigs and make accurate variant calling at low frequencies. Many samples come from host tissues where ribosomal RNA represents more than 90% of total RNA preparations, making unbiased sequencing of viral samples inefficient and highly expensive, as many reads will be wasted on cellular RNAs. In the presence of this amount of ribosomal RNA, it is difficult to achieve sufficient sequencing depth to perform analyses such as variant calling, haplotype prediction, virus population analyses, virus discovery or transcriptomic profiling. Many methods for depleting unwanted RNA or enriching RNA of interest have been devised, including poly-A selection, RNase H based specific depletion, duplex-specific nuclease treatment and hybrid capture selection, among others. Although these methods can be efficient, they either cannot be used for some viruses (i.e. non-polyadenylated viruses), have been optimized for use in a single species, or have the potential to introduce bias. In this study, we describe a novel approach that uses an RNaseH possessing reverse transcriptase coupled with selective probes for ribosomal RNA designed to work broadly for three medically relevant mosquito genera; Aedes, Anopheles, and Culex. We demonstrate significant depletion of rRNA using multiple assessment techniques from a variety of sample types, including whole mosquitoes and mosquito midgut contents from FTA cards. To demonstrate the utility of our approach, we describe novel insect-specific virus genomes from numerous species of field collected mosquitoes that underwent rRNA depletion, thereby facilitating their detection. The protocol is straightforward, relatively low-cost and requires only common laboratory reagents and the design of several small oligonucleotides specific to the species of interest. This approach can be adapted for use with other organisms with relative ease, thus potentially aiding virus population genetics analyses, virus discovery and transcriptomic profiling in both laboratory and field samples.

microbiology↗