Species-specific chemosensory gene expression in the olfactory organs of the malaria vector Anopheles gambiae.

BACKGROUND: The malaria mosquito Anopheles gambiae has a high preference for human hosts, a characteristic that contributes greatly to its capacity for transmitting human malaria. A sibling species, An. quadriannulatus, has a quite different host preference and feeds mostly on bovids. For this reason it does not contribute to human malaria transmission. Host seeking in mosquitoes is modulated by the olfactory system, which is primarily housed in the antennae and maxillary palps. Therefore, the detection of differing host odors by sibling species may be reflected in the expression level of the olfactory genes involved. Accordingly, we compared the transcriptomes of the antennae and maxillary palps of An. gambiae and An. quadriannulatus. RESULTS: We identified seven relatively abundant olfactory receptors, nine ionotropic receptors and three odorant binding proteins that are substantially up-regulated in An. gambiae antennae. Interestingly, we find that the maxillary palps of An. gambiae contain a species-specific olfactory receptor, Or52, and five An. gambiae-specific gustatory receptors (AgGr48-52) that are relatively abundant. These five gustatory receptors are also expressed in An. gambiae antennae, although at lower level, indicating a likely role in olfaction, rather than gustation. We also document an approximately three-fold higher overall expression of olfaction genes in the maxillary palps of An. quadriannulatus, indicating an important role of this organ in the olfaction system of this species. Finally, the expression of the CO2 receptor genes is five to six-fold higher in the zoophilic An. quadriannulatus, implying a much higher sensitivity for detecting CO2. CONCLUSIONS: These results identify potential human host preference genes in the malaria vector An. gambiae. Interestingly, species-specific expression of several gustatory receptors in the olfactory organs indicate a role in olfaction rather than gustation. Additionally, a more expansive role for maxillary palps in olfaction is implicated than previously thought, albeit more so in the zoophilic An. quadriannulatus.

Genomic evidence of sex chromosome aneuploidy and infection-associated genotypes in the tsetse fly Glossina fuscipes, the major vector of African trypanosomiasis in Uganda.

The primary vector of the trypanosome parasite causing human and animal African trypanosomiasis in Uganda is the riverine tsetse fly Glossina fuscipes fuscipes (Gff). Our study improved the Gff genome assembly with whole genome 10× Chromium sequencing of a lab reared pupae, identified autosomal versus sex-chromosomal regions of the genome with ddRAD-seq data from 627 field caught Gff, and identified SNPs associated with trypanosome infection with genome-wide association (GWA) analysis in a subset of 351 flies. Results from 10× Chromium sequencing greatly improved Gff genome assembly metrics and assigned a full third of the genome to the sex chromosome. Results from ddRAD-seq suggested possible sex-chromosome aneuploidy in Gff and identified a single autosomal SNP to be highly associated with trypanosome infection. The top associated SNP was ∼1100 bp upstream of the gene lecithin cholesterol acyltransferase (LCAT), an important component of the molecular pathway that initiates trypanosome lysis and protection in mammals. Results suggest that there may be naturally occurring genetic variation in Gff in genomic regions in linkage disequilibrium with LCAT that can protect against trypanosome infection, thereby paving the way for targeted research into novel vector control strategies that can promote parasite resistance in natural populations.

Genome-wide Association Study Reveals New Loci Associated With Pyrethroid Resistance in Aedes aegypti.

Genome-wide association studies (GWAS) use genetic polymorphism across the genomes of individuals with distinct characteristics to identify genotype-phenotype associations. In mosquitoes, complex traits such as vector competence and insecticide resistance could benefit from GWAS. We used the Aedes aegypti 50k SNP chip to genotype populations with different levels of pyrethroid resistance from Northern Brazil. Pyrethroids are widely used worldwide to control mosquitoes and agricultural pests, and their intensive use led to the selection of resistance phenotypes in many insects including mosquitoes. For Ae. aegypti, resistance phenotypes are mainly associated with several mutations in the voltage-gated sodium channel, known as knockdown resistance (kdr). We phenotyped those populations with the WHO insecticide bioassay using deltamethrin impregnated papers, genotyped the kdr alleles using qPCR, and determined allele frequencies across the genome using the SNP chip. We identified single-nucleotide polymorphisms (SNPs) directly associated with resistance and one epistatic SNP pair. We also observed that the novel SNPs correlated with the known kdr genotypes, although on different chromosomes or not in close physical proximity to the voltage gated sodium channel gene. In addition, pairwise comparison of resistance and susceptible mosquitoes from each population revealed differentiated genomic regions not associated with pyrethroid resistance. These new bi-allelic markers can be used to genotype other populations along with kdr alleles to understand their worldwide distribution. The functional roles of the genes near the newly discovered SNPs require new studies to determine if they act synergistically with kdr alleles or reduce the fitness cost of maintaining resistant alleles.

Genetic structure of the mosquito Aedes aegypti in local forest and domestic habitats in Gabon and Kenya.

BACKGROUND: The mosquito Aedes aegypti is a devastating disease vector transmitting several important human arboviral diseases. In its native range in Africa, the mosquito can be found in both the ancestral forest habitat and anthropogenic habitats such as villages. How do the different habitats impact the population genetic structure of the local mosquito populations? METHODS: To address this question, we simultaneously sampled Ae. aegypti from the forest and local villages in La Lopé, Gabon and Rabai, Kenya. The mosquitoes were genotyped at 12 microsatellite loci and a panel of ~25,000 single nucleotide polymorphisms (SNPs), which allowed us to estimate their genetic ancestries and the population genetic structure related to habitats and sampling sites. RESULTS: In the context of the global population genetic structure of Ae. aegypti, clustering analysis showed that mosquitoes from the same locality (La Lopé or Rabai) have similar genetic ancestry, regardless of their habitats. Further analysis at the local scale also found no strong genetic differentiation between the forest and village mosquitoes in both La Lopé and Rabai. Interestingly, these results from our 2017 samples from Rabai, Kenya contrast to the documentation of genetic differentiation between village and forest mosquito collections from 1975-1976 and 2009. Between-habitat measures of genetic difference (Fst) vary across the genome, with a peak of high divergence observed at the third chromosome only in the La Lopé populations. CONCLUSION: Collectively, these results demonstrated that there is little genetic isolation between forest and village habitats, which suggests possible extensive gene flow between them. From an epidemiological perspective, the forest habitat could act as a refuge for mosquitoes against vector control programmes in the domestic settings. Moreover, sylvatic populations could play a role in zoonotic pathogen transferred to humans. Therefore, future studies on disease transmission and vector control planning in the study area should take natural populations into consideration.

Improved reference genome of the arboviral vector Aedes albopictus.

BACKGROUND: The Asian tiger mosquito Aedes albopictus is globally expanding and has become the main vector for human arboviruses in Europe. With limited antiviral drugs and vaccines available, vector control is the primary approach to prevent mosquito-borne diseases. A reliable and accurate DNA sequence of the Ae. albopictus genome is essential to develop new approaches that involve genetic manipulation of mosquitoes. RESULTS: We use long-read sequencing methods and modern scaffolding techniques (PacBio, 10X, and Hi-C) to produce AalbF2, a dramatically improved assembly of the Ae. albopictus genome. AalbF2 reveals widespread viral insertions, novel microRNAs and piRNA clusters, the sex-determining locus, and new immunity genes, and enables genome-wide studies of geographically diverse Ae. albopictus populations and analyses of the developmental and stage-dependent network of expression data. Additionally, we build the first physical map for this species with 75% of the assembled genome anchored to the chromosomes. CONCLUSION: The AalbF2 genome assembly represents the most up-to-date collective knowledge of the Ae. albopictus genome. These resources represent a foundation to improve understanding of the adaptation potential and the epidemiological relevance of this species and foster the development of innovative control measures.

Effective population sizes of a major vector of human diseases, Aedes aegypti.

The effective population size (Ne ) is a fundamental parameter in population genetics that determines the relative strength of selection and random genetic drift, the effect of migration, levels of inbreeding, and linkage disequilibrium. In many cases where it has been estimated in animals, Ne is on the order of 10%-20% of the census size. In this study, we use 12 microsatellite markers and 14,888 single nucleotide polymorphisms (SNPs) to empirically estimate Ne in Aedes aegypti, the major vector of yellow fever, dengue, chikungunya, and Zika viruses. We used the method of temporal sampling to estimate Ne on a global dataset made up of 46 samples of Ae. aegypti that included multiple time points from 17 widely distributed geographic localities. Our Ne estimates for Ae. aegypti fell within a broad range (~25-3,000) and averaged between 400 and 600 across all localities and time points sampled. Adult census size (Nc) estimates for this species range between one and five thousand, so the Ne /Nc ratio is about the same as for most animals. These Ne values are lower than estimates available for other insects and have important implications for the design of genetic control strategies to reduce the impact of this species of mosquito on human health.

[Toxicity of pesticides used in chrysanthemum crops to eggs and nymphs of Orius insidiosus (Say) (Hemiptera: Anthocoridae)]. / Toxicidade de produtos fitossanitários utilizados na cultura do crisântemo para ovos e ninfas de Orius insidiosus (Say) (Hemiptera: Anthocoridae).

The objective of this study was to evaluate the toxicity of some pesticides used in chrysanthemum crops to eggs and nymphs of Orius insidiosus (Say). The bioassays were carried out at 25 +/- 2 degrees C, 70 +/- 10% RH and 12h photophase. For the tests with eggs, stems of Bidens pilosa L. previously exposed to predator oviposition were dipped for five seconds in aqueous dilution of the pesticides, using 40 eggs per treatment. The pesticides were applied on nymphs using a Potter's tower. Forty first-instar and twenty second-instar nymphs of O. insidiosus were used per treatment in the tests with nymphs. The adults from eggs and nymphs treated were grouped in couples to study the pesticides effects on its reproductive parameters. None tested pesticide affected the viability of treated eggs. Azoxystrobin, benomyl, imibenconazole, iprodione, metalaxyl + mancozeb and triforine were harmless to first- and second-instar nymphs of O. insidiosus, whereas abamectin, acephate and chlorfenapyr were shown to be harmful to nymphs of both first and second instars. The pre-oviposition period, the daily number of eggs, number of eggs in ten days, and egg viability were not affected by azoxystrobin, benomyl, imibenconazole, iprodione, metalaxyl + mancozeb and triforine. These pesticides, for showing low toxicity to the predator, can be recommended in disease management programs for chrysanthemum crops, in association with O. insidiosus.

Toxicidade de produtos fitossanitários utilizados na cultura do crisântemo para ovos e ninfas de Orius insidiosus ( Say ) ( Hemiptera: Anthocoridae ) / Toxicity of pesticides used in chrysanthemum crops to eggs and nymphs of Orius insidiosus ( Say ) ( Hemiptera: Anthocoridae )

O objetivo do presente estudo foi avaliar a toxicidade de alguns produtos fitossanitários utilizados na cultura do crisântemo para ovos e ninfas de Orius insidiosus (Say). Os bioensaios foram conduzidos em condições de laboratório a 25 ± 2°C, UR de 70 ± 10 por cento e fotofase de 12h. O contato dos produtos com os ovos foi realizado pela imersão de hastes de picão-preto (Bidens pilosa L.), previamente expostas para oviposição, nas caldas químicas dos produtos por um período de cinco segundos. Os produtos foram aplicados sobre ninfas por meio de torre de Potter. Foram utilizadas 40 ninfas de primeiro ínstar e 20 ninfas de segundo ínstar de O. insidiosus por tratamento. Adultos oriundos de ovos e ninfas tratados foram agrupados em casais para estudar o efeito dos produtos sobre seus parâmetros reprodutivos. Nenhum dos compostos avaliados afetou a viabilidade dos ovos tratados. Azoxistrobim, benomil, imibenconazole, iprodione, metalaxil + mancozebe e triforine foram seletivos para os insetos de primeiro e segundo ínstares de O. insidiosus tratados, enquanto abamectina, acefato e clorfenapir mostraram-se tóxicos para indivíduos de ambos os ínstares. O período de pré-oviposição, o número médio diário de ovos colocados, o número total de ovos por dez dias e a viabilidade de ovos também não foram afetados negativamente por azoxistrobim, benomil, imibenconazole, iprodione, metalaxil + mancozebe e triforine. Esses compostos, devido à baixa toxicidade apresentada, podem ser recomendados em programas de manejo de doenças na cultura do crisântemo, em associação com O. insidiosus.

Seletividade de inseticidas para ovos e ninfas de Orius insidiosus ( Say ) ( Hemiptera: Anthocoridae ) / Selectivity of inseticides to eggs and nymphs of Orius insidiosus ( Say ) ( Hemiptera: Anthocoridae )

O predador Orius insidiosus (Say) alimenta-se de tripes, afídeos, moscas-brancas, ácaros e pequenas lagartas, contribuindo para a regulação populacional dessas pragas em diferentes agroecossistemas. Este trabalho teve por objetivo avaliar a seletividade dos inseticidas abamectina, cartape, ciromazina, fempropatrina e imidaclopride, registrados para a cultura do crisântemo, para ovos e ninfas de 1°, 2° e 3° instares de O. insidiosus. Os produtos foram pulverizados em torre de Potter, sendo utilizadas as maiores doses recomendadas para o controle de pragas na cultura do crisântemo. Após a pulverização, os ovos e ninfas foram mantidos em condições controladas, com temperatura de 25 ± 1°C, UR de 70 ± 10 por cento e fotofase de 12h. Avaliaram-se a duração do período embrionário, a viabilidade dos ovos e a duração e sobrevivência de ninfas. Os ovos de O. insidiosus foram tolerantes a todos os inseticidas. Cartape e ciromazina foram seletivos às ninfas de 1°, 2° e 3° ínstares, enquanto que os demais produtos foram tóxicos. Fempropatrina provocou 100 por cento de mortalidade de O. insidiosus nos três ínstares avaliados. Os inseticidas cartape e ciromazina podem ser recomendados para uso em programas de manejo integrado de pragas na cultura do crisântemo.

Toxicidade de produtos fitossanitários utilizados na cultura do cafeeiro a larvas de Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) e efeitos sobre as fases subseqüentes do desenvolvimento do predador / Toxicity of pesticides used in coffee crops to larvae of Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) and their effects on subsequent stages of the predator

Avaliou-se a seletividade fisiológica de alguns produtos fitossanitários utilizados em cafeeiro a larvas de Chrysoperla externa (Hagen) e seus reflexos nas fases subseqüentes do desenvolvimento do predador. Os tratamentos avaliados, em g i.a./L de água foram: 1- endosulfam (Thiodan 350 CE - 1,75), 2- clorpirifós (Lorsban 480 CE - 1,2), 3- betaciflutrina (Turbo 50 CE - 0,013), 4- enxofre (Kumulus 800 PM - 4,0), 5- azociclotina (Peropal 250 PM - 0,31), 6- oxicloreto de cobre (Cuprogarb 500 PM - 5,0) e 7- testemunha (água). As pulverizações foram realizadas em larvas de primeiro, segundo e terceiro ínstares de C. externa, por meio de torre de Potter. Em seguida, as larvas foram individualizadas em tubos de vidro e mantidas em câmara climatizada regulada a 25 ± 2°C, UR de 70 ± 10 por cento e fotofase de 12h. A toxicidade dos produtos foi calculada em função do seu efeito total (E) e categorizada conforme escala proposta pela IOBC. Clorpirifós e betaciflutrina foram nocivos a larvas de primeiro ínstar (E > 99 por cento) e os demais foram seletivos. Clorpirifós foi também tóxico a larvas de segundo e terceiro ínstares, sendo os demais compostos inócuos ao predador (E < 30 por cento). Nenhum dos produtos avaliados afetou a duração e sobrevivência de pupas, ou a razão sexual e fase adulta dos indivíduos provenientes de larvas tratadas. Endosulfam, enxofre, azociclotina e oxicloreto de cobre foram seletivos para larvas de primeiro, segundo e terceiro ínstares de C. externa e não afetaram as fases subseqüentes do desenvolvimento desse crisopídeo, podendo ser utilizados no manejo de pragas na cultura do cafeeiro.

The objective was to evaluate the selectivity of pesticides used in coffee crops to larvae of Chrysoperla externa (Hagen) and their effects on the subsequent developmental stages of the predator. The treatments in g a.i./L of water were: 1 - endosulfan (Thiodan 350 CE - 1.75), 2 - chlorpyrifos (Lorsban 480 CE - 1.2), 3 - betacyfluthrin (Turbo 50 CE - 0.013), 4 - sulphur (Kumulus 800 PM - 4.0), 5 - azocyclotin (Peropal 250 PM - 0.31), 6 - copper oxichloride (Cuprogarb 500 PM - 5.0) and 7 - control (water). The products were sprayed on first, second and third-instar larvae using a Potter's tower. The larvae were individualized in glass tubes and maintained at 25 ± 2°C, RH of 70 ± 10 percent and 12h photophase. The toxicity of the pesticides was calculated based in their total effect (E) and classified according to recommendations of IOBC. Chlorpyrifos and betacyfluthrin were harmful to first-instar larvae (E > 99 percent). Endosulfan, sulphur, azocyclotin and copper oxichloride were harmless to first-instar larvae and the others were selective. Chlorpyrifos was also toxic to second and third-instar larvae, and the other compounds were selective (E < 30 percent). None of the pesticides affected the duration and survival rate of pupae or the sex ratio of the adults originated from treated larvae. Endosulfan, sulphur, azocyclotin and copper oxichloride were harmless to the larval stage of C. externa and did not affect the subsequent stages, so that they can be recommended in IPM programs for the coffee crop.

Seletividade de seis inseticidas utilizados em citros a pupas e adultos de Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) / Selectivity of six insecticides used in citrus crops on pupae and adults of Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae)

The selectivity of the insecticides abamectin, lufenuron, fenbutatin oxide, tebufenozide, thiacloprid and deltamethrin used in citrus crops was evaluated for pupae and adults of Chrysoperla externa (Hagen). The experiments were conducted in the Entomology Department of the Universidade Federal de Lavras, MG, Brazil. The spraying was accomplished by means of Potter tower with volume ofapplication of 1.5 ± 0.5 mg/cm2. After spraying, the pupae were kept in test tubes in a climatic chamber and the adults in PVC cages in a room at 25 ± 2oC, 70 ± 10% RH and 12h photophase. A completely randomized experimental design was used, with six products and ten replicates, each one composed of three pupae or a pair of adults. The action of lufenuron on males or females of C. externa was also evaluated under acompletely randomized design with three treatments and ten replicates, each one composed of one pair. The insecticides were classified following the method established by the International Organization for Biological and Integrated Control of Noxious Animals and Plants (IOBC). All compounds were selective to the pupae (E < 30% of mortality). However, thiacloprid and deltamethrin were toxic to the adults (E > 99% of mortality), whereas fenbutatin oxide and tebufenozide were selective. Lufenuron reduced the survival rate of the egg when sprayed on the females. Thus, the results indicate that only fenbutatin oxide and tebufenozide could be used with C. externa in integrated pest management programs in citrus crops.

Avaliou-se a seletividade dos inseticidas abamectina, lufenurom, óxido de fenbutatina, tebufenozide, tiaclopride e deltametrina utilizados em citros para pupas e adultos de Chrysoperla externa (Hagen). Os experimentos foram conduzidos no Departamento de Entomologia da UFLA, Lavras, MG. As pulverizações foram realizadas por meio de torre de Potter utilizando-se 1,5 ± 0,5 mg/ cm2. Após a pulverização, as pupas foram colocadas em tubos de vidro e mantidas em câmara climática,e os adultos em gaiolas de PVC em sala climatizada (25 ± 2oC, 70 ± 10% UR e fotofase de 12h). O delineamento experimental foi inteiramente casualizado com seis inseticidas e dez repetições, sendo cada uma formada por três pupas ou um casal de adultos. Também foi avaliado o efeito do lufenurom na capacidade reprodutiva quando pulverizado sobre machos ou fêmeas desse predador. Os produtosforam enquadrados em classes de toxicidade seguindo metodologia estabelecida pela Organização Internacional para Controle Biológico e Integrado de Animais e Plantas Nocivos (IOBC). Todos os produtos foram seletivos para pupas (E < 30% de mortalidade). Tiaclopride e deltametrina foram tóxicos aos adultos (E > 99% de mortalidade), sendo que óxido de fenbutatina e tebufenozide mostraram-seseletivos. Quando pulverizado somente sobre fêmeas de C. externa, lufenurom reduziu significativamente a viabilidade de ovos. Os produtos óxido de fenbutatina e tebufenozide, em função da baixa toxicidade apresentada, podem ser recomendados no manejo integrado de pragas na cultura dos citros emassociação com C. externa.

Seletividade de inseticidas utilizados na cultura dos citros para ovos e larvas de Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) / Selectivity of insecticides used in citrus crops to eggs and larvae of Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae)

The objective of this work was to evaluate the selectivity of abamectin (0.0054 g a.i. L-1), deltamethrin (0.0125 g a.i. L-1), fenbutatin oxide (0.4 g a.i. L-1), lufenuron (0.0375 g a.i. L-1), tebufenozide (0.12 g a.i. L-1) and thiacloprid (0.036 g a.i. L-1) to eggs and larvae of Chrysoperla externa (Hagen). Commercial formulations of the insecticides were diluted in water and sprayed, using a Potter’s tower,at 1.5 ± 0.5 mg.cm-2, either on eggs or on glass plates, where first, second and third-instar larvae were placed to assess the contact action on them. Egg viability, survival of larvae, pupae and adults, and the effects of the compounds on the reproductive capacity of individuals were evaluated. The total toxic effect (E) of the insecticides was calculated according to the standard methodology established by IOBC. All tested insecticides were selective for eggs of C. externa. Lufenuron and deltamethrin were highly toxic to first, second and third-instar larvae of C. externa (E > 99% of mortality). Abamectin, fenbutatin oxide, tebufenozide and thiacloprid were moderately toxic to larvae of C. externa. First-instar larvae were the most sensitive to the compounds. All tested insecticides need to be tested undergreenhouse and field conditions, to further evaluate their suitability for IPM programs in citrus crops.

Objetivou-se neste trabalho avaliar a seletividade dos inseticidas abamectina (0,0054 g i.a. L-1), deltametrina (0,0125 g i.a. L-1), óxido de fenibutatina (0,4 g i.a. L-1), lufenurom (0,0375 g i.a. L-1), tebufenozide (0,12 g i.a. L-1) e tiaclopride (0,036 g i.a. L-1) para ovos e larvas de Chrysoperla externa (Hagen). Os inseticidas foram pulverizados, por meio de torre de Potter, garantindo a aplicação de 1,5± 0,5 mg/cm2, nos ovos ou em placas de vidro, sobre as quais foram colocadas larvas de primeiro, segundo e terceiro ínstares. Avaliaram-se a viabilidade dos ovos, a sobrevivência de larvas, pupas eadultos e o efeito dos inseticidas na capacidade reprodutiva dos indivíduos oriundos de ovos e de larvas tratadas. A toxicidade dos inseticidas foi calculada em função do seu efeito total (E), conforme metodologia padrão estabelecida pela “IOBC”. Todos os inseticidas foram seletivos para ovos de C. externa. Lufenurom e deltametrina foram altamente nocivos a larvas de primeiro, segundo e terceiro ínstares de C. externa (E > 99% de mortalidade). Abamectina, óxido de fenibutatina, tebufenozide e tiaclopride apresentaram toxicidade intermediária à fase larval de C. externa. O primeiro ínstar dessepredador foi o mais susceptível à ação dos produtos avaliados. Recomenda-se avaliar os efeitos dos inseticidas testados para larvas de C. externa em condições de casa de vegetação e campo para confirmação de sua toxicidade e possível utilização em programas de manejo integrado de pragas em citros.