Impact of Agriculture on the Selection of Insecticide Resistance in the Malaria Vector Anopheles gambiae : A Multigenerational Study in Controlled Conditions.

Resistance of mosquitoes to insecticides is mainly attributed to their adaptation to vector control interventions. Although pesticides used in agriculture have been frequently mentioned as an additional force driving the selection of resistance, only a few studies were dedicated to validate this hypothesis and characterise the underlying mechanisms. While insecticide resistance is rising dramatically in Africa, deciphering how agriculture affects resistance is crucial for improving resistance management strategies. In this context, the multigenerational effect of agricultural pollutants on the selection of insecticide resistance was examined in Anopheles gambiae. An urban Tanzanian An. gambiae population displaying a low resistance level was used as a parental strain for a selection experiment across 20 generations. At each generation larvae were selected with a mixture containing pesticides and herbicides classically used in agriculture in Africa. The resistance levels of adults to deltamethrin, DDT and bendiocarb were compared between the selected and non-selected strains across the selection process together with the frequency of kdr mutations. A microarray approach was used for pinpointing transcription level variations selected by the agricultural pesticide mixture at the adult stage. A gradual increase of adult resistance to all insecticides was observed across the selection process. The frequency of the L1014S kdr mutation rose from 1.6% to 12.5% after 20 generations of selection. Microarray analysis identified 90 transcripts over-transcribed in the selected strain as compared to the parental and the non-selected strains. Genes encoding cuticle proteins, detoxification enzymes, proteins linked to neurotransmitter activity and transcription regulators were mainly affected. RT-qPCR transcription profiling of candidate genes across multiple generations supported their link with insecticide resistance. This study confirms the potency of agriculture in selecting for insecticide resistance in malaria vectors. We demonstrated that the recurrent exposure of larvae to agricultural pollutants can select for resistance mechanisms to vector control insecticides at the adult stage. Our data suggest that in addition to selected target-site resistance mutations, agricultural pollutants may also favor cuticle, metabolic and synaptic transmission-based resistance mechanisms. These results emphasize the need for integrated resistance management strategies taking into account agriculture activities

Toll-8/Tollo Negatively Regulates Antimicrobial Response in the Drosophila Respiratory Epithelium

Barrier epithelia that are persistently exposed to microbes have evolved potent immune tools to eliminate such pathogens. If mechanisms that control Drosophila systemic responses are well-characterized, the epithelial immune responses remain poorly understood. Here, we performed a genetic dissection of the cascades activated during the immune response of the Drosophila airway epithelium i.e. trachea. We present evidence that bacteria induced-antimicrobial peptide (AMP) production in the trachea is controlled by two signalling cascades. AMP gene transcription is activated by the inducible IMD pathway that acts non-cell autonomously in trachea. This IMD-dependent AMP activation is antagonized by a constitutively active signalling module involving the receptor Toll-8/Tollo, the ligand Spätzle2/DNT1 and Ect-4, the Drosophila ortholog of the human Sterile alpha and HEAT/ARMadillo motif (SARM). Our data show that, in addition to Toll-1 whose function is essential during the systemic immune response, Drosophila relies on another Toll family member to control the immune response in the respiratory epithelium

Gene silencing of the kynurenine pathway and melanotic lesions in the malaria mosquito vector anopheles gambiae

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Melanotic Pathology and Vertical Transmission of the Gut Commensal <i>Elizabethkingia</i><i> meningoseptica</i> in the Major Malaria Vector <i>Anopheles gambiae</i>

<div><p>Background</p><p>The resident gut flora is known to have significant impacts on the life history of the host organism. Endosymbiotic bacterial species in the <i>Anopheles</i> mosquito gut are potent modulators of sexual development of the malaria parasite, <i>Plasmodium</i>, and thus proposed as potential control agents of malaria transmission.</p> <p>Results</p><p>Here we report a melanotic pathology in the major African malaria vector <i>Anopheles gambiae</i>, caused by the dominant mosquito endosymbiont <i>Elizabethkingia</i><i>meningoseptica</i>. Transfer of melanised tissues into the haemolymph of healthy adult mosquitoes or direct haemolymph inoculation with isolated <i>E</i><i>. meningoseptica</i> bacteria were the only means for transmission and <i>de</i><i>novo</i> formation of melanotic lesions, specifically in the fat body tissues of recipient individuals. We show that <i>E</i><i>. meningoseptica</i> can be vertically transmitted from eggs to larvae and that <i>E</i><i>. meningoseptica</i>-mono-associated mosquitoes display significant mortality, which is further enhanced upon <i>Plasmodium</i> infection, suggesting a synergistic impact of <i>E</i><i>. meningoseptica</i> and <i>Plasmodium</i> on mosquito survival.</p> <p>Conclusion</p><p>The high pathogenicity and permanent association of <i>E</i><i>. meningoseptica</i> with <i>An. Gambiae</i> through vertical transmission constitute attractive characteristics towards the potential design of novel mosquito/malaria biocontrol strategies.</p> </div

Induction of lesions by injection of melanotic tissues in <i>Anopheles</i> species.

<p>(<b>A</b>) Melanotic fat body tissues induce lethality in injected mosquitoes. Adult females were injected with abdomen-derived fat body tissues of melanotic lesion-bearing or of control adult females. Melanotic fat body extracts (FBE) were injected using two dilutions (1XFBE crude extract or 10-fold diluted extract 0.1XFBE). Survival rate was monitored daily, and represented as bars with standard error, as a percentage for each group. Three biologically independent injection assays were performed with 15-20 mosquitoes per condition. Points indicated by *** are very highly significantly different (P<0.05) between FBE control and 1XFBE or 0.1XFBE values.(<b>B</b>) Light micrographs of fat body tissues derived from FBE-injected female mosquitoes. Melanotic lesions in <i>An</i>. <i>gambiae</i> (<i>upper </i><i>panel</i>; scale bar 0.05mm), and <i>An</i>. <i>stephensi</i> (<i>lower </i><i>panel</i>; scale bar 0.5mm) mosquito species, resembling melanotic aggregates in the fat body of the affected ‘donor’ mosquito (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077619#pone-0077619-g001" target="_blank">Figure 1</a>).</p

Melanotic phenotypes throughout <i>An</i><i>gambiae</i> developmental stages.

<p>(<b>A</b>) Melanotic lesions in the mosquito fat body throughout the developmental stages (<i>left </i><i>panels</i>; scale bar ~1mm). Variation in shape and size of lesions with clusters and multiple melanised cells in a trail-like progression (<i>right </i><i>panel</i>; scale bar ~0.5mm) (<b>B</b>) Phenotypic larval lesions. Light micrographs (left panels) and fixed samples (right panels). Melanotic lesions diffused throughout the larval body (<i>upper </i><i>panels</i>; arrows). Lesions specific to abdominal segments (<i>middle </i><i>left </i><i>panel</i>; white arrow head) visible through the cuticle below the siphon (S). Fixed abdominal segments showing complete melanisation of the 8^th segment (<i>middle </i><i>left </i><i>panel</i>; dotted area). Thoracic melanotic lesions (T) (<i>lower </i><i>left </i><i>panel</i>; white arrows), and a fixed larva with four lesions (lowest right panel) (black white arrows); H, head; T, thorax. Scale bar ~1mm. (<b>C</b>) Prevalence of melanotic phenotypes throughout the mosquito development is indicated as bars corresponding to the mean value +/- SD of 3 experiments. Abdominal, Abd; Diffused, Diff; Thoracic, Thorax. (<b>D</b>) Diffused phenotype in pupae. A light micrograph of a non-affected pupa (upper panel) and a fixed affected pupa with the diffused phenotype (lowest panel) showing melanotic lesions throughout the thorax (T) and abdomen (A) (black arrowheads). Scale bar ~1mm. (<b>E</b>) Lesions in adult mosquitoes. Melanotic abdominal lesions are observed at the junction between the 7^th and 8^th abdominal segments of female and male mosquitoes (<i>upper </i><i>panels</i>; white arrows). Partially dissected abdominal segments from the same specimens (lowest panels) revealing melanotic aggregates (white arrows). Scale bar ~1mm. (<b>F</b>) Lesion-bearing mosquitoes survive poorly after thoracic injury. Groups of 40-60 female mosquitoes with lesions (L1, L2, L3) and corresponding controls without lesions (C1, C2, C3) were injured in the thorax below the base of the wing. Survival rate was monitored at 1, 3 and 6 days post-injury. Points indicated by *** are statistically very highly significant (P<0.05) between L and C.</p

Executive Committee - Agenda, 6/6/1991

Background Resistance of mosquitoes to insecticides is a growing concern in Africa. Since only a few insecticides are used for public health and limited development of new molecules is expected in the next decade, maintaining the efficacy of control programmes mostly relies on resistance management strategies. Developing such strategies requires a deep understanding of factors influencing resistance together with characterizing the mechanisms involved. Among factors likely to influence insecticide resistance in mosquitoes, agriculture and urbanization have been implicated but rarely studied in detail. The present study aimed at comparing insecticide resistance levels and associated mechanisms across multiple Anopheles gambiae sensu lato populations from different environments. Methods Nine populations were sampled in three areas of Tanzania showing contrasting agriculture activity, urbanization and usage of insecticides for vector control. Insecticide resistance levels were measured in larvae and adults through bioassays with deltamethrin, DDT and bendiocarb. The distribution of An. gambiae sub-species and pyrethroid target-site mutations (kdr) were investigated using molecular assays. A microarray approach was used for identifying transcription level variations associated to different environments and insecticide resistance. Results Elevated resistance levels to deltamethrin and DDT were identified in agriculture and urban areas as compared to the susceptible strain Kisumu. A significant correlation was found between adult deltamethrin resistance and agriculture activity. The subspecies Anopheles arabiensis was predominant with only few An. gambiae sensu stricto identified in the urban area of Dar es Salaam. The L1014S kdr mutation was detected at elevated frequency in An gambiae s.s. in the urban area but remains sporadic in An. arabiensis specimens. Microarrays identified 416 transcripts differentially expressed in any area versus the susceptible reference strain and supported the impact of agriculture on resistance mechanisms with multiple genes encoding pesticide targets, detoxification enzymes and proteins linked to neurotransmitter activity affected. In contrast, resistance mechanisms found in the urban area appeared more specific and more related to the use of insecticides for vector control. Conclusions Overall, this study confirmed the role of the environment in shaping insecticide resistance in mosquitoes with a major impact of agriculture activities. Results are discussed in relation to resistance mechanisms and the optimization of resistance management strategies

Open Access

Insecticide resistance mechanisms associated with different environments in the malaria vecto

Contrasting patterns of tolerance between chemical and biological insecticides in mosquitoes exposed to UV-A

International audienc

UV light and urban pollution: Bad cocktail for mosquitoes?

International audienc