Evaluation of the larvicide effect of an aqueous extract of Persea americana (Miller, 1768), Lauraceae,on Anopheles gambine (Giles, 1902), Diptera Culicidae

Summary

In-laboratory evaluation of the larvicide effect of an aqueous extract of Persea americana (Miller 1768) on the various larval stages of Anopheles gambiae (Giles 1902) has shown that larvae at all stages are sensitive to this extract. Inversely proportional to the larval stage, their sensitivity proved to depend on the level of concentration: the higher the latter, the higher the former. Indeed, after a 24-h exposure, concentrations of 510 μg/ml resulted in the death of 100% of larvae at stages 1 and 2, whereas for the same time of exposure there was need to resort to concentrations of 850 μg/ml to kill them at stages 3 and 4. The aqueous extract of Persea americana has therefore a poisonous effect on larvae of Anopheles gambiae. This extract has direct lethal effects and acts as an inhibitor of larval development at sublethal concentration levels.     

Malaria entomological risk factors in relation to land cover in the Lower Caura River Basin,Venezuela

To explore the effects of deforestation and resulting differences in vegetation and land cover on entomological parameters, such as anopheline species composition, abundance, biting rate, parity and entomological inoculation rate (EIR), three villages were selected in the Lower Caura River Basin, state of Bolívar, Venezuela. All-night mosquito collections were conducted between March 2008-January 2009 using CDC light traps and Mosquito Magnet^(r) Liberty Plus. Human landing catches were performed between 06:00 pm-10:00 pm, when anophelines were most active. Four types of vegetation were identified. The Annual Parasite Index was not correlated with the type of vegetation. The least abundantly forested village had the highest anopheline abundance, biting rate and species diversity. Anopheles darlingi and Anopheles nuneztovari were the most abundant species and were collected in all three villages. Both species showed unique biting cycles. The more abundantly forested village of El Palmar reported the highest EIR. The results confirmed previous observations that the impacts of deforestation and resulting changes in vegetation cover on malaria transmission are complex and vary locally.     

Increased presence of the thermophilic mosquitoes and potential vectors Anopheles hyrcanus (Pallas 1771) and Culex modestus Ficalbi 1889 in Central Europe’s lower Dyje River basin (South Moravia,Czech Republic)

The presence of the thermophilic species Anopheles hyrcanus in the lower Dyje River basin has been regularly monitored since 2008. Mosquito trapping has been conducted mainly in summer using EVS traps with CO₂ as attractant. Anopheles hyrcanus and Culex modestus were studied in a group of ponds near the Czech–Austrian border. At the Sedlec location, occurrence of An. hyrcanus was low during 2008–2011, with around 1–9 individuals/trap/collection day. At the Lednice location on the edge of Mlýnský Pond, the first capture of An. hyrcanus occurred in 2010. In 2013, there was a sudden increase in the An. hyrcanus mosquito at all monitored locations. The largest presence was recorded at Sedlec and reached 524.4 individuals/trap/collection day. Culex modestus was one of the predominant species throughout the period. At Sedlec, the smallest finding was in 2009 (at 9.6 individuals) while the greatest was in 2010 (at 988.6 individuals/trap/collection day). At Lednice, the smallest finding was in 2011 (at 56.3 individuals) while the largest was in 2013 (at 3850 individuals/trap/collection day).     

Lethal effects of Gliocladium virens,Beauveria bassiana and Metarhizium anisopliae on the malaria vector Anopheles albimanus (Diptera: Culicidae)

Control of Anopheles albimanus, the main vector of malaria on the coast of the State of Chiapas, is based mainly on application of chemical insecticides, which has resulted in resistance to most registered insecticides. Strategies for biological control may provide sustainable alternatives. We report on the lethal effects of a native isolate of Gliocladium virens on An. albimanus larvae and adults, compared to that of strains of Beauveria bassiana and Metarhizium anisopliae. Conidial suspensions of G. virens, B. bassiana and M. anisopliae cultured on Sabouraud agar were tested in bioassays with An. albimanus larvae and adults. Mosquito larvae were more susceptible to all fungi, compared to adults. On early and late instar larvae, M. anisopliae showed the most pathogenic effect (LC₅₀ of 1.4×10⁵ conidia/mL in early instars; 1.1×10⁵ conidia/mL in late instars), followed by G. virens (LC₅₀ of 3.3×10⁵ conidia/mL in early instars and 3.5×10⁶ conidia/mL in late instars). Metarhizium anisopliae sensu lato and the native G. virens could be considered good choices for An. albimanus control in southern Mexico.     

A novel mechanism of ligand binding and release in the odorant binding protein 20 from the malaria mosquito Anopheles gambiae

Anopheles gambiae mosquitoes that transmit malaria are attracted to humans by the odor molecules that emanate from skin and sweat. Odorant binding proteins (OBPs) are the first component of the olfactory apparatus to interact with odorant molecules, and so present potential targets for preventing transmission of malaria by disrupting the normal olfactory responses of the insect. AgamOBP20 is one of a limited subset of OBPs that it is preferentially expressed in female mosquitoes and its expression is regulated by blood feeding and by the day/night light cycles that correlate with blood‐feeding behavior. Analysis of AgamOBP20 in solution reveals that the apo‐protein exhibits significant conformational heterogeneity but the binding of odorant molecules results in a significant conformational change, which is accompanied by a reduction in the conformational flexibility present in the protein. Crystal structures of the free and bound states reveal a novel pathway for entrance and exit of odorant molecules into the central‐binding pocket, and that the conformational changes associated with ligand binding are a result of rigid body domain motions in α‐helices 1, 4, and 5, which act as lids to the binding pocket. These structures provide new insights into the specific residues involved in the conformational adaptation to different odorants and have important implications in the selection and development of reagents targeted at disrupting normal OBP function.     

Transstadial immune activation in a mosquito: Adults that emerge from infected larvae have stronger antibacterial activity in their hemocoel yet increased susceptibility to malaria infection

Larval and adult mosquitoes mount immune responses against pathogens that invade their hemocoel. Although it has been suggested that a correlation exists between immune processes across insect life stages, the influence that an infection in the hemocoel of a larva has on the immune system of the eclosed adult remains unknown. Here, we used Anopheles gambiae to test whether a larval infection influences the adult response to a subsequent bacterial or malaria parasite infection. We found that for both female and male mosquitoes, a larval infection enhances the efficiency of bacterial clearance following a secondary infection in the hemocoel of adults. The adults that emerge from infected larvae have more hemocytes than adults that emerge from naive or injured larvae, and individual hemocytes have greater phagocytic activity. Furthermore, mRNA abundance of immune genes—such as cecropin A, Lysozyme C1, Stat‐A, and Tep1—is higher in adults that emerge from infected larvae. A larval infection, however, does not have a meaningful effect on the probability that female adults will survive a systemic bacterial infection, and increases the susceptibility of females to Plasmodium yoelii, as measured by oocyst prevalence and intensity in the midgut. Finally, immune proficiency varies by sex; females exhibit increased bacterial killing, have twice as many hemocytes, and more highly express immune genes. Together, these results show that a larval hemocoelic infection induces transstadial immune activation—possibly via transstadial immune priming—but that it confers both costs and benefits to the emerged adults.     

Plasmodium yoelii: the effect of second blood meal and anti-sporozoite antibodies on development and gene expression in the mosquito vector, Anopheles stephensi

The sporogonic development of the malaria parasite takes place in the mosquito and a wide range of factors modulates it. Among those, the contents of the blood meal can influence the parasite development directly or indirectly through the mosquito response to the infection. We have studied the effect of a second blood meal in previously infected mosquitoes and the effect of anti-sporozoite immune serum on parasite development and mosquito response to the infection. The prevalence and intensity of infection and gene expression of both Plasmodium yoelii and Anopheles stephensi was analyzed. We verified that a second blood meal and its immune status interfere with parasite development and with Plasmodium and mosquito gene expression.     

New selenoproteins identified in silico from the genome of Anopheles gambiae

Selenoprotein is biosynthesized by the incorporation of selenocysteine into proteins,where the TGA codon in the open reading frame does not act as a stop signal but is translated into selenocysteine.The dual functions of TGA result in mis-annotation or lack of selenoproteins in the sequenced genomes of many species.Available computational tools fail to correctly predict selenoproteins.Thus,we devel-oped a new method to identify selenoproteins from the genome of Anopheles gambiae computationally.Based on released genomic information,several programs were edited with PERL language to identify selenocysteine insertion sequence(SECIS)element,the coding potential of TGA codons,and cys-teine-containing homologs of selenoprotein genes.Our results showed that 11365 genes were termi-nated with TGA codons,918 of which contained SECIS elements.Similarity search revealed that 58 genes contained Sec/Cys pairs and similar flanking regions around in-frame TGA codons.Finally,7 genes were found to fully meet requirements for selenoproteins,although they have not been anno-tated as selenoproteins in NCBI databases.Deduced from their basic properties,the newly found se-lenoproteins in the genome of Anopheles gambiae are possibly related to in vivo oxidation tolerance and protein regulation in order to interfere with anopheles' vectorial capacity of Plasmodium.This study may also provide theoretical bases for the prevention of malaria from anopheles transmission.