A Population Genomic Assessment of Three Decades of Evolution in a Natural Drosophila Population

Population genetics seeks to illuminate the forces shaping genetic variation, often based on a single snapshot of genomic variation. However, utilizing multiple sampling times to study changes in allele frequencies can help clarify the relative roles of neutral and non-neutral forces on short time scales. This study compares whole-genome sequence variation of recently collected natural population samples of Drosophila melanogaster against a collection made approximately 35 years prior from the same locality - encompassing roughly 500 generations of evolution. The allele frequency changes between these time points would suggest a relatively small local effective population size on the order of 10,000, significantly smaller than the global effective population size of the species. Some loci display stronger allele frequency changes than would be expected anywhere in the genome under neutrality - most notably the tandem paralogs Cyp6a17 and Cyp6a23, which are impacted by structural variation associated with resistance to pyrethroid insecticides. We find a genome-wide excess of outliers for high genetic differentiation between old and new samples, but a larger number of adaptation targets may have affected SNP-level differentiation versus window differentiation. We also find evidence for strengthening latitudinal allele frequency clines: northern-associated alleles have increased in frequency by an average of nearly 2.5% at SNPs previously identified as clinal outliers, but no such pattern is observed at random SNPs. This project underscores the scientific potential of using multiple sampling time points to investigate how evolution operates in natural populations, by quantifying how genetic variation has changed over ecologically relevant timescales.

Pyrethroid insecticides susceptibility of Stomoxys calcitrans (Linnaeus) and Stomoxys indicus Picard (Diptera: Muscidae) from cattle farms in southern Thailand

The susceptibility to six pyrethroid insecticides (permethrin, deltamethrin, alpha-cypermethrin, cypermethrin, lambda-cyhalothrin and bifenthrin), each at the recommended concentration, was evaluated for the two stable fly species Stomoxys calcitrans (Linnaeus) and Stomoxys indicus Picard, through tarsal contact using a World Health Organization (WHO) cone bioassay procedure. The field populations of stable flies were collected from three study sites (Songkhla, Phattalung and Satun provinces) in Thailand. The stable flies were exposed to insecticide-treated filter paper for 30 min and their knockdown counts at 30 min and 60 min and mortality counts at 12 hr and 24 hr were recorded. The S. calcitrans and S. indicus in Songkhla and Phattalung populations were moderately susceptible to pyrethroids for 24-hr mortality. Nonetheless, the Satun population of S. indicus was completely susceptible to permethrin with 100% mortality and the lowest susceptible to deltamethrin and bifenthrin. The results indicate a generally low susceptibility of stable flies to pyrethroids in the southern provinces of Thailand.

Deteksi Gen Kdr pada Nyamuk Anopheles di Kabupaten Maluku Tenggara Barat

Malaria is still a health problem in Indonesia, particularly in Eastern part of Indonesia. The use of LLIN insecticide bed nets is one of the efforts to reduce the malaria morbidity rate by protecting human from malaria vector bites. The Anopheles flavirostris, Anopheles barbirostris, and Anopheles subpictus mosquitoes are three of the species reported as malaria vectors in West-Southeast Maluku Regency. The aim of this research was to detect the kdr gene in An. flavirostris, An. barbirostris, and An.subpictus mosquitoes collected from Alusi Kelaan village, West-Southeast Maluku Regency. The research was conducted at the Papua Biomedical Research and Development Center, in June 2016. A total of six An. flavirostris, 42 An. barbirostris, and 24 An. subpictus were pooled separately for genomic DNA extraction. The sample used was the An. flavirostris, An. barbirostris, and An. subpictus that survived after the impregnated paper test. The kdr gene detection was carried out using quantitative PCR (qPCR) focused on points V1010 and L1014. The results showed that there were no kdr mutant strains in the An. flavirostris, An. barbirostris, and An. subpictus. These results indicated that the sensitivity of pyrethroid insecticides contained in LLIN mosquito nets to An. flavirostris, An. barbirostris, and An. subpictus mosquitoes was not decreased in West Southeast Maluku Regency.

Molecular surveillance of resistance to pyrethroids insecticides in Colombian Aedes aegypti populations

Introduction In Colombia, organochloride, organophosphate, carbamate, and pyrethroid insecticides are broadly used to control Aedes aegypti populations. However, Colombian mosquito populations have shown variability in their susceptibility profiles to these insecticides, with some expressing high resistance levels. Materials and methods In this study, we analyzed the susceptibility status of ten Colombian field populations of Ae. aegypti to two pyrethroids; permethrin (type-I pyrethroid) and lambda-cyhalothrin (type-II pyrethroid). In addition, we evaluated if mosquitoes pressured with increasing lambda-cyhalothrin concentrations during some filial generations exhibited altered allelic frequency of these kdr mutations and the activity levels of some metabolic enzymes. Results Mosquitoes from all field populations showed resistance to lambda-cyhalothrin and permethrin. We found that resistance profiles could only be partially explained by kdr mutations and altered enzymatic activities such as esterases and mixed-function oxidases, indicating that other yet unknown mechanisms could be involved. The molecular and biochemical analyses of the most pyrethroid-resistant mosquito population (Acacías) indicated that kdr mutations and altered metabolic enzyme activity are involved in the resistance phenotype expression. Conclusions In this context, we propose genetic surveillance of the mosquito populations to monitor the emergence of resistance as an excellent initiative to improve mosquito-borne disease control measures.

Transcriptomic modulation in response to an intoxication with deltamethrin in Triatoma infestans, vector of Chagas disease

Background: Triatoma infestans is the main vector of Chagas disease in the Southern Cone. The resistance to pyrethroid insecticides developed by populations of this species impairs the effectiveness of vector control campaigns in wide regions of Argentina. The study of the global transcriptomic response to pyrethroid insecticides is important to deepen the knowledge about detoxification in triatomines. Methodology and findings: We used RNA-Seq to explore the early transcriptomic response of T. infestans after intoxication with deltamethrin. We were able to assemble a complete transcriptome of this vector and found evidence of differentially expressed genes belonging to diverse families such as chemosensory and odorant-binding proteins, ABC transporters and heat-shock proteins. Moreover, genes related to transcription and translation, energetic metabolism and cuticle rearrangements were also modulated. Finally, we characterized the repertoire of previously uncharacterized detoxification-related gene families in T. infestans and Rhodnius prolixus. Conclusions and significance: Our work contributes to the understanding of the detoxification response in vectors of Chagas disease. Given the absence of genomic information from T. infestans, the analysis presented here constitutes a resource for molecular and physiological studies in this species. The results increase the knowledge on detoxification processes in vectors of Chagas disease, and provide relevant information to explore new potential insecticide resistance mechanisms in these insects.

Transcriptomic and proteomic analysis of pyrethroid resistance in the CKR strain of Aedes aegypti

Aedes aegypti is an important vector of human viral diseases. This mosquito is distributed globally and thrives in urban environments, making it a serious risk to human health. Pyrethroid insecticides have been the mainstay for control of adult A. aegypti for decades, but resistance has evolved, making control problematic in some areas. One major mechanism of pyrethroid resistance is detoxification by cytochrome P450 monooxygenases (CYPs), commonly associated with the overexpression of one or more CYPs. Unfortunately, the molecular basis underlying this mechanism remains unknown. We used a combination of RNA-seq and proteomic analysis to evaluate the molecular basis of pyrethroid resistance in the highly resistant CKR strain of A. aegypti. The CKR strain has the resistance mechanisms from the well-studied Singapore (SP) strain introgressed into the susceptible Rockefeller (ROCK) strain genome. The RNA-seq and proteomics data were complimentary; each offering insights that the other technique did not provide. However, transcriptomic results did not quantitatively mirror results of the proteomics. There were 10 CYPs which had increased expression of both transcripts and proteins. These CYPs appeared to be largely trans-regulated, except for some CYPs for which we could not rule out gene duplication. We identified 65 genes and lncRNAs as potentially being responsible for elevating the expression of CYPs in CKR. Resistance was associated with multiple loci on chromosome 1 and at least one locus on chromosome 3. We also identified five CYPs that were overexpressed only as proteins, suggesting that stabilization of CYP proteins could be a mechanism of resistance. Future studies to increase the resolution of the resistance loci, and to examine the candidate genes and lncRNAs identified here will greatly enhance our understanding of CYP-mediated resistance in A. aegypti.

Alternative Strategies for Controlling the Brown Locust, Locustana pardalina (Walker)

Regular and often intense outbreaks of the brown locust, Locustana pardalina (Walker), in the semi-arid Nama Karoo region of South Africa present a formidable pest control problem. Outbreak patterns over a 64-year period (1941–2005) were reviewed indicating a very high frequency of outbreak years with regular ‘plague’ periods being experienced, while a more detailed analysis of the numbers of locust targets controlled during a 22-year period (1983–2005) described the intensity and scale of the outbreaks. The operational constraints associated with the traditional ground-based control strategy employed against the thousands of individual roosting brown locust hopper band and swarm targets in the Karoo are discussed. A brief review of laboratory and field trials of alternative methods of controlling the brown locust, such as insecticide baits, barrier treatments and the Green Muscle® myco-insecticide, as an alternative to broad-spectrum pyrethroid insecticides are described. In addition, alternative control strategies to the current ‘Commando’ system of ground-based control operations are discussed. The recommendation is for a modernised and technology-equipped integrated brown locust management strategy (IPM), combining ground and aerial tactics that will have the flexibility and the capacity to deal effectively with outbreaks. The integrated management strategy should focus on ground-based control of hopper bands and fledgling swarms in the Upper and eastern Karoo, while outbreaks over most of the Central Karoo and arid Bushmanland areas should be left to fledge and coalesce into large-sized swarms that could then be targeted by spray aircraft as they migrate along their known swarm flight paths. The introduction of electronic reporting and GIS mapping technologies for brown locust campaign management is essential.

Decade Long Upsurge In Target Site Pyrethroid Resistance In Bed Bug Populations In The United States

Over the past three decades, the bed bug Cimex lectularius has resurged as a prominent indoor pest on a global scale. Knockdown-associated insecticide resistance (kdr) involving the voltage-gated sodium channel, targeted by organochlorine and pyrethroid insecticides, was first reported in C. lectularius within a few years of the widespread use of Dichlorodiphenyltrichloroethane (DDT) and has been implicated as a significant factor contributing to the species recent resurgence. Since then, selection with pyrethroid insecticides has intensified, yet little is known regarding its short-term impacts on the frequency of kdr-associated mutations. Here, we report temporal changes in the frequencies of three kdr-associated mutations in C. lectularius populations collected across the United States from two time periods, sampled approximately a decade apart. Results reveal a significant increase in the frequencies of kdr-associated mutations over this period, and absence of the insecticide-susceptible genotype in recent collections. Furthermore, a significant transition towards infestations possessing multiple kdr-associated mutations was observed. These results suggest that the persistent use of pyrethroid insecticides over the past decade continues to impose strong selection pressure on C. lectularius populations, driving the proliferation of kdr-associated mutations. They demonstrate that, if unabated, strong anthropogenic selection can drive the rapid evolution of adaptive traits.