Biology subjects

Saavedra-Rodriguez, K.

Publications and source records attributed to Saavedra-Rodriguez, K..

4 recordsLinked to original sources

bioRxiv2026

Biparental vertical transmission of Aedes anphevirus, Guadeloupe mosquito virus, and verdadero virus in colonized Aedes aegypti

Aedes aegypti mosquitoes can be infected by arboviruses that can be transmitted to and cause disease in vertebrates. Ae. aegypti can also be infected by insect-specific viruses, which do not infect vertebrates, but may impact mosquito biology and vector competence. In this study we characterized the viromes of Ae. aegypti populations that had been maintained in laboratory colonies for 4 to 18 years. Mosquitoes were originally collected in Tapachula, Poza Rica and Merida, Mexico and New Orleans, USA. We used metagenomics to characterize the viruses present in the colonies, then quantified the vertical transmission efficiencies of the viruses by performing crosses between populations. The viruses infecting these colonies included Aedes anphevirus, Guadeloupe mosquito virus, and verdadero virus. These viruses were at high prevalence in infected populations, with over 75% of individual adult mosquitoes infected. All three viruses exhibited biparental vertical transmission: both infected mothers and infected fathers transmitted infection to their offspring, but in all cases maternal transmission was more efficient than paternal. We also identified evidence of possible horizontal transmission between adult mosquitoes that had cohabited during crosses. Efficient transgenerational transmission likely contributes to the ability of these viruses to persist in laboratory populations and nature. Because of their efficient vertical transmission and minimal apparent fitness costs, these viruses could be good candidates for gene delivery to mosquito populations, including for vector control. Author summaryAedes aegypti mosquitoes are responsible for transmission of many dangerous pathogens, including dengue virus, Zika virus, and yellow fever virus. These mosquitoes also carry viruses that do not pose a threat to public health, but might influence mosquito biology. In this study, we identified viruses that persistently infected 4 long-established Ae. aegypti colonies in our insectary. These viruses were at high prevalence in these laboratory populations, and did not appear to harm infected mosquitoes. The viruses exhibited an ability to efficiently transmit from parents to offspring, both from infected mothers and infected fathers. This provided an explanation for how these mosquitoes were able to persist so successfully in laboratory populations, and by extension in nature. Given their ability to efficiently spread and minimal apparent fitness costs, these viruses represent promising candidates for use in mosquito control or other practical applications.

microbiology↗

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↗

bioRxiv2017

Improved Aedes aegypti mosquito reference genome assembly enables biological discovery and vector control

Female Aedes aegypti mosquitoes infect hundreds of millions of people each year with dangerous viral pathogens including dengue, yellow fever, Zika, and chikungunya. Progress in understanding the biology of this insect, and developing tools to fight it, has been slowed by the lack of a high-quality genome assembly. Here we combine diverse genome technologies to produce AaegL5, a dramatically improved and annotated assembly, and demonstrate how it accelerates mosquito science and control. We anchored the physical and cytogenetic maps, resolved the size and composition of the elusive sex-determining \"M locus\", significantly increased the known members of the glutathione-S-transferase genes important for insecticide resistance, and doubled the number of chemosensory ionotropic receptors that guide mosquitoes to human hosts and egg-laying sites. Using high-resolution QTL and population genomic analyses, we mapped new candidates for dengue vector competence and insecticide resistance. We predict that AaegL5 will catalyse new biological insights and intervention strategies to fight this deadly arboviral vector.

genomics↗