Permethrin-impregnated bednets: behavioural and killing effects on mosquitoes

Permethrin-treated pieces of netting and simulated bednets were evaluated against Anopheles gambiae Giles and Aedes aegypti (L.) in the laboratory. When female mosquitoes were allowed to feed on a human arm through pieces of impregnated netting fastened at the end of tubes, doses above 2 g/m2 were required to stop blood-feeding of both An. gambiae and Ae. aegypti. A much lower dose prevented Ae. aegypti from feeding on mice through impregnated netting. When mosquitoes were released in a room and a human subject sat under a permethrin-impregnated (0.2 g/m2) bednet with an arm pressed against the net (mesh 1.5 mm), mosquitoes failed to bite through the net. All the mosquitoes trying to bite through or entering the net through holes cut in it were knocked down within 30 min of release and ultimately died. Permethrin-impregnated wide-mesh (4 or 8 mm) bednets similarly prevented entry and caused high mortality-rates of An. gambiae.     

Ovicidal and larvicidal activity against Aedes aegypti and Anopheles gambiae complex mosquitoes of essential oils extracted from three spontaneous plants of Burkina Faso

Essential oils extracted from dried leaves of three spontaneous plants naturally growing in Burkina Faso, i.e. Cymbopogon proximus, Lippia multiflora and Ocimum canum, exhibited larvicidal activity by the WHO standard protocol against 3rd and 4th instar F1-larvae of field-collected mosquitoes vectors of human disease, namely Aedes aegypti and members of the Anopheles gambiae complex, An. arabiensis and An. gambiae. The median lethal concentration (LC50) for Ae. aegypti and An. gambiae s.l. larvae ranged between 53.5-258.5 ppm and 61.9-301.6 ppm, respectively. The LC90 estimates ranged 74.8-334.8 ppm for Ae. aegypti, and 121.6-582.9 ppm for An. gambiae s.l. Ovicidal activity against eggs of An. gambiae s.l. was also demonstrated. The LC50 values for An. gambiae s.l. eggs ranged between 17.1-188.7 ppm, while LC90 values ranged between 33.5-488 ppm. Lippia multiflora showed the highest activity against An. gambiae s.l. eggs and Ae. aegypti larvae, whereas no difference was found among C. proximus and L. multiflora in their activity against An. gambiae s.l. larvae. Of the three plants, essential oils from O. canum had the lowest activity against both eggs and larvae. Eggs were more susceptible than larvae. Ae. aegypti larvae were more susceptible than larvae of An. gambiae s.l.     

Laboratory and field evaluation of commercial repellent formulations against mosquitoes (Diptera: Culicidae) in Queensland, Australia

Abstract  Laboratory tests of commercial repellent formulations were conducted against Anopheles farauti Laveran, Culex annulirostris Skuse, Ochlerotatus vigilax (Skuse) and Stegomyia aegypti (L.). The majority of repellent formulations tested contain N,N ,-diethyl- 3 -methylbenzamide (also known as diethyl- m -toluamide, commonly called deet). Two formulations containing picaridin (1-piperidinecarboxylate acid, 2-(2-hydroxyethyl)-1-methylpropylester, also known as KBR 3023), one containing ethyl butylacetylaminopropionate (EBAP) and two formulations containing essential oils (e.g. Citronella oil) were also tested. In the laboratory tests, repellent formulations containing deet provided the best protection, and picaridin and EBAP also provided good protection. Citronella oil provided only limited protection. Two field trials to compare commercially available repellent formulations containing picaridin and deet against mosquitoes at Redcliffe, Queensland, were conducted. In the first, Autan Repel, containing 9.3% picaridin, RID, containing 10% deet, and Bushman Ultra, containing 80% deet in a gel, were compared. In the second, Autan Repel Army 20, containing 19.2% picaridin, OFF! Skintastic, containing 7% deet, and Aerogard, containing 12% deet, were compared. The predominant mosquito in both tests was Cx. annulirostris . Bushman provided >95% protection against all mosquitoes for at least 8 h when tests ceased. The other deet repellents also provided good protection against mosquitoes, with RID providing 5 h, Skintastic 4 h and Aerogard 2 h protection. The Autan repel (9.3% picaridin) provided >95% protection for 3 h, and Autan Repel Army (19.2% picaridin) provided 4 h protection. These studies have shown that commercial formulations of both deet and picaridin provide good protection against Cx. annulirostris , an important vector of arboviruses in Australia.     

Comparative repellency of commercial formulations of deet, permethrin and citronellal against the mosquito Aedes aegypti, using a collagen membrane technique compared with human arm tests

A collagen membrane technique, based on the membrane blood-feeding system of Cosgrove et al . (1994) , was used to compare repellents against Aedes aegypti mosquitoes. Repellency was defined in terms of inhibition of probing (ED₅₀ and ED₉₀) after 5 min exposure. A direct comparison was made with repellency from probing after 5 min on five male volunteers.
Four repellent products were compared with technical DEET as the standard. The liquid formulations tested were: Autan^® (20% deet; Bayer); Repel Plus^® (20% deet plus 0.05% permethrin; Boots); permethrin (Zeneca) and citronellal (Sigma) .
Membrane and arm tests gave similar results. Deet formulations required less active compound than citronellal for the same degree of repellency. Pure deet and Autan gave similar results, dose for dose. Permethrin was highly repellent at very low doses, but Repel Plus did not enhance the immediate repellency of deet. A technique using the same membrane system was developed to evaluate persistence of Autan, which declined to 75% after 1 h against Ae. aegypti , and to about 50% after 2–4 h.     

QSAR study of mosquito repellents using Codessa Pro

Protection times provided by 31 synthetic repellents against Aedes aegypti mosquitoes were correlated with the chemical structures of these repellents using Codessa Pro software. Two statistically significant quantitative models with R2 values of ca. 0.80 are presented and discussed.     

Experimental hut trials of bednets impregnated with synthetic pyrethroid or organophosphate insecticide for mosquito control in The Gambia

1. Nylon bednets impregnated with different insecticides were evaluated in 1988 against wild adult mosquito populations, mostly Mansonia africana (Theobald) and Anopheles gambiae Giles sensu lato, entering experimental verandah-trap huts in The Gambia. Each bednet had six 10 x 10 cm holes made in the walls to simulate torn conditions and permit female mosquitoes to enter and feed on sleepers. 2. Individual net treatments, determined by gas chromatography of net samples from before and after 12 weeks use of the bednets, were: permethrin 670 +/- 159 and 405 +/- 190 mg/m2 (40% loss), cypermethrin 37 +/- 8 and 16 +/- 9 mg/m2 (57% loss), deltamethrin 10 +/- 7 and 10 +/- 8 mg/m2 (no loss), lambda-cyhalothrin 2.6 +/- 0.9 and 1.6 +/- 0.5 mg/m2 (38% loss), pirimiphos-methyl 4017 +/- 117 and 1160 +/- 319 mg/m2 (71% loss). 3. Washing three times in the traditional manner with local cow-fat soap reduced the initial dosages by about 85% of cypermethrin and lambda-cyhalothrin, 99.8% of pirimiphos-methyl and left no detectable residues of deltamethrin or permethrin. 4. The unwashed permethrin-treated bednet reduced the number of mosquitoes entering a hut by 60% of An.gambiae s.l. and 68% of Mansonia spp. This deterrency was less pronounced with the other insecticides and was lost by washing the bednets. 5. Each insecticide, especially lambda-cyhalothrin and pirimiphosmethyl, caused significant mortality rates of mosquitoes that entered huts with impregnated bednets, and prevented the majority of An. gambiae s.l. and Mansonia females from bloodfeeding. Washing completely removed the efficacy of deltamethrin and permethrin treated bednets, whereas nets treated with cypermethrin, lambda-cyhalothrin or pirimiphos-methyl remained significantly insecticidal after washing. 6. Aerial toxicity from the pirimiphos-methyl treated bednet killed 80% of An.gambiae s.l. confined overnight in the hut at the end of the trial, whereas the pyrethroid-treated bednets gave negligible mortality rates of mosquitoes. 7. Sleepers using the bednets had no medical symptoms significantly associated with any of the treatments. On the contrary, from 216 interviews, 4/10 complaints were associated with the use of untreated nets (P approximately 0.05), perhaps because sleepers were kept awake by mosquitoes and became more aware of any ailments. 8. It is concluded that permethrin tends mainly to deter mosquitoes from house-entry, enhancing personal protection, whereas the other insecticides kill higher proportions of the endophilic mosquitoes, which would give better community protection against malaria transmission.     

Medium for the production of primary powder of Bacillus thuringiensis subsp. israelensis

Five media, formulated from the seeds of five legume varieties, dried cow blood, and mineral salts, were assessed for the growth and production of insecticidal properties of Bacillus thuringiensis subsp. israelensis. Bacterial powders prepared from the broth cultures were assayed against the larvae of Aedes aegypti, Culex quinquefasciatus, and Anopheles gambiae. A standard primary powder of B. thuringiensis subsp. israelensis (IPS78) was included in the assay for comparison. Good growth was obtained in all the media, and all powders were effective against the three types of mosquito larvae. The powder containing ground seeds of Voandzeia subterranean was the most effective and compared favorably with the standard (IPS78). The concentrations required to kill 50% of the larvae of Aedes aegypti, C. quinquefasciatus, and Anopheles gambiae were 1.13 X 10(-2) +/- 1.79 X 10(-3), 1.83 X 10(-2) +/- 2.55 X 10(-3), and 2.25 X 10(-2) +/- 1.88 X 10(-3) micrograms/ml, respectively. This investigation shows that the medium containing V. subterranean can be used for the production of B. thuringiensis subsp. israelensis primary powder.     

Medium for the production of primary powder of Bacillus thuringiensis subsp. israelensis.

Five media, formulated from the seeds of five legume varieties, dried cow blood, and mineral salts, were assessed for the growth and production of insecticidal properties of Bacillus thuringiensis subsp. israelensis. Bacterial powders prepared from the broth cultures were assayed against the larvae of Aedes aegypti, Culex quinquefasciatus, and Anopheles gambiae. A standard primary powder of B. thuringiensis subsp. israelensis (IPS78) was included in the assay for comparison. Good growth was obtained in all the media, and all powders were effective against the three types of mosquito larvae. The powder containing ground seeds of Voandzeia subterranean was the most effective and compared favorably with the standard (IPS78). The concentrations required to kill 50% of the larvae of Aedes aegypti, C. quinquefasciatus, and Anopheles gambiae were 1.13 X 10(-2) +/- 1.79 X 10(-3), 1.83 X 10(-2) +/- 2.55 X 10(-3), and 2.25 X 10(-2) +/- 1.88 X 10(-3) micrograms/ml, respectively. This investigation shows that the medium containing V. subterranean can be used for the production of B. thuringiensis subsp. israelensis primary powder.     

Olyset Net efficacy against pyrethroid-resistant Anopheles gambiae and Culex quinquefasciatus after 3 years' field use in C te d'Ivoire

Pyrethroid-impregnated bednets are advocated for personal protection against malaria vectors. To avoid the need for periodic re-treatment, it would be advantageous to have nets that retain insecticidal efficacy for years and withstand repeated washing. Such a type of commercially produced bednet with permethrin 2% incorporated in polyethylene fibres (trademark Olyset Net supplied by Sumika Life-Tech Co., Osaka, Japan) was evaluated against mosquitoes in veranda-trap huts at Yaokoffikro, near Bouaké, C te d'Ivoire, by standard WHOPES phase II procedures. Four Olyset Nets were compared with a standard untreated polyester net as control. They comprised three examples previously used in a village for over 3 years (one washed, one dirty, one very dirty) and a previously unused Olyset Net, newly unwrapped, from the same original batch. Bioassays with 3 min exposure of susceptible Anopheles gambiae Giles (Diptera: Culicidae) gave >99% mortality of female mosquitoes tested on the 'new' Olyset Net. The used Olyset Nets gave mortality rates averaging 83% for the washed net, 85% for the dirty net and 55% for the very dirty net (within 24-h following 3 min exposure). Thus, Olyset Nets were found to remain remarkably effective against susceptible An. gambiae for at least 3 years under field conditions. Wild pyrethroid-resistant populations of Culex quinquefasciatus Say and An. gambiae (savanna cytotype with 96% kdr) were assessed during June-August 1999 for their responses to sleepers protected by nets in the experimental huts. With regard to hut entry by foraging female mosquitoes, Olyset Nets showed some deterrency against An. gambiae (44% reduction by the new net, approximately 20% by the dirty nets, none by the washed net), but not against Cx. quinquefasciatus. Among mosquitoes entering the hut with untreated control net, 30-34% tried to leave (exophily) but were caught in the verandah trap. The permethrin repellency of Olyset Nets increased exophily by 19% for An. gambiae and 14% for Cx. quinquefasciatus. Blood-feeding rates were 16% An. gambiae and 35% Cx. quinquefasciatus in the hut with sleeper under the untreated net (showing considerable prevention of biting), 22-26% of both species in huts with washed or dirty used Olyset Nets (not significantly different from control), while the biting success rate of Cx. quinquefasciatus (but not kdr An. gambiae) was more than halved by the 'new' Olyset Net. Mortality rates of pyrethroid-resistant An. gambiae and Cx. quinquefasciatus from the huts were, respectively, 3% and 8% with the untreated polyester net, 27.5% and 17% with the 'new' Olyset, 15% and 17.5% with the washed Olyset, 16-25% and 17-20% with dirty old Olyset Nets. Kill differences between nets are significantly different for both An. gambiae and Cx. quinquefasciatus. Unfortunately the washed used Olyset Net showed least activity against resistant mosquitoes, despite its greatest activity against susceptible An. gambiae. In each case there was evidence that a high proportion of mosquitoes failed to feed through the net (many of them dying from starvation when they could not leave the closed hut), with indications that dirty Olyset nets enhanced this protective value.     

Synergistic effects of essential oil-based cream formulations against Culex quinquefasciatus Say and Aedes aegypti L. (Diptera: Culicidae)

Mosquitoes are major arthropod vectors responsible for several pathogenic diseases. In recent years, repellents of botanical origin, particularly essential oils, have been used against mosquitoes and have been found effective and safe. In this study, five different repellent cream formulations (CF1–5) were prepared using combinations of essential oils, including camphor, cinnamon, citronella, lemongrass, lime, orange, neem, basil, Vitex, Lantana, eucalyptus, and clove, and their repellency was tested using Culex quinquefasciatus Say and Aedes aegypti L. under laboratory conditions and compared to the standard synthetic repellent N,N-diethyl-meta-toluamide (DEET-12%, w/w). Among the five cream formulations, CF2 at a dose of 5 mg/cm² showed the longest protection time of 4.18 h and 3.31 h against C. quinquefasciatus and A. aegypti, respectively, under laboratory conditions. CF3 at a dose of 5 mg/cm² was moderately effective, with protection times of 3.42 h and 2.58 h against C. quinquefasciatus and A. aegypti, respectively, under laboratory conditions. CF2 at a dose of 5 mg/cm² was also tested in the field against wild mosquitoes for 3 h, and 100% protection was observed for the entire study period. Thus, CF2 could be used in developing an effective natural repellent as an alternative to the existing synthetic repellents to C. quinquefasciatus and A. aegypti.     

Thanaka (Limonia acidissima) and deet (di-methyl benzamide) mixture as a mosquito repellent for use by Karen women

The prevention and treatment of drug-resistant malaria is becoming increasingly difficult. On the Thai–Myanmar border multi-drug resistant strains of falciparum malaria are increasing and, because the malaria vector Anopheles bite outdoors during early evening, insecticide house-spraying or impregnated bednets provide only limited protection. Therefore, the protective efficacy of repellent formulations containing di-methyl benzamide (deet) and permethrin against local vectors was estimated, when applied to the skin, and their acceptability amongst pregnant Karen women who are at relatively high risk from malaria was assessed. Human landing catches of mosquitoes showed that almost complete protection was achieved using different formulations of 20% deet and 0.5% permethrin for up to 6 h. All-night collections from human subjects indicated that this repellent combination reduced exposure to malaria parasites by at least 65 and 85% for those transmitted by Anopheles minimus and An. maculatus , respectively, the two principal vectors in this area. Pregnant women in the camps preferred repellents which were mixed with 'thanaka', a root paste made from pulp of the wood apple tree, Limonia acidissima , used locally as a cosmetic. Apart from a temporary warming sensation where repellent thanaka was applied to the skin, the repellents were well tolerated. An intervention trial is currently in progress to determine whether deet mixed with thanaka can protect pregnant women against malaria in this part of the world. Bioassays using a laboratory strain of Aedes aegypti demonstrated that thanaka is itself slightly repellent at high dosages and the mixture with deet provides protection for over 10 h. This treatment would therefore also provide some personal protection against dengue, which is increasing locally, transmitted by Ae. aegypti and Ae. albopictus biting during the daytime.     

Switchover to the mated state by spermathecal activation in female Anopheles gambiae mosquitoes

Both Aedes aegypti and Anopheles gambiae mosquitoes undergo physiological and behavioral changes after the females mate, but unlike Ae. aegypti, the mated state in An. gambiae is not attained through the action of male accessory gland substances. Experiments in which the spermathecae of mated females were manipulated suggest that a spermatheca filled with sperm is responsible for triggering oviposition behavior. An estimated 48% of the previously mated An. gambiae females mated again when the interval between encounters with males was less than 24h. Unlike male Ae. aegypti that can inseminate up to seven females after their testes are removed, An. gambiae do not store sperm in the vas deferens and without testes would be unable to inseminate any females.     

Production of Bacillus sphaericus strain 1593 primary powder on media made from locally obtainable Nigerian agricultural products

Five media, formulated from dried cow blood, mineral salts, and seeds from four species of legumes, were assessed for growth, sporulation, and insecticidal properties of Bacillus sphaericus strain 1593. Bacterial powders, prepared from broth, were assayed against Culex quinquefasciatus, Anopheles gambiae, and Aedes aegypti. Good growth and sporulation were obtained with all the media. The highest number of viable cells and spores per mililitre (8.6 X 10(8) and 8.1 X 10(8] were obtained in media containing ground seeds of Vignia unguiculata, Voandzeia subterranean, and Arachis hypogea. All powders were effective against C. quinquefasciatus and A. gambiae. Powders from media containing Arachis hypogea were the most effective with LC50's of 4.344 X 10(-3) +/- 1.650 X 10(-4) and 0.193 +/- 1.376 X 10(-2) micrograms/mL for C. quinquefasciatus and A. gambiae, respectively. Aedes aegypti larvae were only slightly susceptible to the powders. This investigation shows that these media can be used for the production of B. sphaericus 1593 primary powder.     

Lethal and behavioural effects of three synthetic repellents (DEET, IR3535 and KBR 3023) on Aedes aegypti mosquitoes in laboratory assays

The knock-down, mortality and 'irritancy' effects of three synthetic repellents (DEET, IR3535 and KBR 3023) on Aedes aegypti (L) (Diptera: Culicidae) were evaluated in the laboratory in the absence of animal bait. Filter paper tests were carried out to assess the knock-down effect (KDt(50) and KDt(95)) and mortality (LC(50) and LC(95)) induced by each repellent. 'Irritancy' tests were carried out to compare the flight response (time to first take-off, or FT) to increasing concentrations of repellents (2-7%) and at five distances from the treated surface (0-40 mm). DEET had an insecticidal effect (KDt(50) = 9.7 min at 7%; CL(50)= 1165 mg/m(2)), whereas IR3535 and KBR 3023 did not. Relative to an untreated control, IR3535 was an irritant (relative irritancy or RI > 1) at doses of 5% and 7% (RI = 17.7 and 9.9, respectively), whereas DEET was an irritant at lower concentrations (RI = 12.3 at 2% DEET). KBR 3023 was the weakest irritant over the same range of concentrations (RI(max) = 3.6 at 6%). DEET was more of an irritant (RI(20) = 9.4) than IR3535 (RI(20) = 2.9) over a range of distances (0-20 mm), and KBR 3023 was not an irritant unless mosquitoes made contact with the treated surface. All three repellents had a significant effect on mosquitoes, but DEET exhibited a more complex mode of action than the others due to its insecticidal properties. The repellents do not behave as a single class of compounds with a common mode of action, but most probably affect different physiological systems in insects. The physiological and molecular mechanisms of repellents, especially DEET, should be investigated to ensure a better use of these molecules for skin applications and/or for treating materials against mosquitoes.     

Feeding and survival of the malaria vector Anopheles gambiae on plants growing in Kenya

The propensity of the malaria vector mosquito Anopheles gambiae Giles (Diptera: Culicidae) to ingest sugars from various plants, and subsequent survival rates, were assessed with laboratory-reared males and females offered eight species of plants commonly cultivated and/or growing wild in western Kenya. In cages (no-choice bioassay), mosquitoes given the opportunity to feed on castorbean (Ricinus communis L.) had the longest survival times (mean and median survival time of 6.99 +/- 0.23 and 5.67 +/- 0.17 days, respectively), comparable to mosquitoes given 6% glucose (mean and median survival time of 8.70 +/- 0.23 and 6.67 +/- 0.33 days, respectively). Survival rates of An. gambiae were low on the other plants, comparable to mosquitoes given only water. Three plants: sweet potato (Ipomoea batatas L.), wild sage (Lantana camara L.) and castorbean provided levels of sugar ingestion by both sexes of An. gambiae detectable using the cold anthrone method, showing a positive correlation between median survival and sugar consumption (Spearman rank correlation coefficient = 0.905, P < 0.0001). Equal numbers of males and females were released in an enclosed semi-field screenhouse system containing a range of local plants, but no host for blood, and allowed to feed ad libitum: 6.7 +/- 0.5% (11/64) of those recaptured were found to contain detectable fructose (all females). Common plants are clearly a viable source of nutrition for adult female An. gambiae, as well as males, and may constitute and important resource for this important malaria vector.     

市售长叶松油和锡兰肉桂油对登革热媒蚊埃及伊蚊的灭幼效果(英文)

松油和桂皮油由于具有芳香性气味, 因而成为良好的成虫驱避剂, 但是关于它们对蚊虫的杀幼虫作用研究不多。为揭示市售的长叶松Pinus longifolia油和锡兰肉桂Cinnamomum zeylanicum油对来源于印度德里的埃及伊蚊Aedes aegypti 4龄幼虫的毒杀潜力, 我们进行了室内研究, 以幼虫死亡率及行为改变和形态改变等指标评估其杀幼虫潜力。结果表明： 两种油对埃及伊蚊4龄幼虫均具有毒杀作用, 且松油的灭幼效果优于桂皮油。松油的LC₅₀和LC₇₀ 值分别为0.33093 mg/L 和0.54476 mg/L, 而桂皮油的LC₅₀和LC₇₀ 值分别为0.63159 mg/L和0.77736。进一步观察发现, LC₉₀剂量下桂皮油的杀幼虫潜力强于松油, 其LC₉₀为1.11879 mg/L, 而松油的LC₉₀为 1.04915 mg/L。在处理的幼虫中观察到行为改变, 如兴奋、 坐立不安、 颤抖、 痉挛然后瘫痪, 说明这两种油可能对其神经肌肉系统产生了影响。显微观察处理幼虫的形态改变发现, 与对照相比, 大多数器官的外观正常, 只是肛鳃略为内收缩而引起结构畸形, 提示肛腮可能是这两种油的作用位点, 腮的功能异常引起了幼虫死亡。这两种油品可开发用作防治蚊虫的新型杀幼虫药剂。     

The relative efficacy of repellents against mosquito vectors of disease

Laboratory tests of insect repellents by various different methods showed that An.stephensi Liston was consistently more susceptible than An.gambiae Giles, An.albimanus Wiedemann or An.pulcherrimus Theobald. The six repellents tested were di-ethyl toluamide (deet), di-methyl phthalate (DMP), ethyl-hexanediol, permethrin, citronella and cedarwood oil. Testing systems in which the mosquitoes were presented with a choice gave consistently lower ED50 values than when there was no choice, i.e. the standards of tolerance are not absolute but depend on the options available. In field tests in an experimental hut a curtain with a high dose of di-ethyl toluamide (deet) reduced biting in the hut but had to be re-impregnated frequently. Deet-impregnated anklets gave about 84% protection against Culex quinquefasciatus Say for 80 days after one impregnation, in a trial in which the anklets were brought out of sealed storage and tested for 2 h nightly. Similar protection was found against An.funestus Giles but the protection against An.gambiae s.l., An. coustani Laveran and Mansonia spp. was not as good. There were highly significant differences between the four collectors' mosquito attractiveness but this varied highly significantly between the mosquito species.     

Responses of Anopheles gambiae, Anopheles stephensi, Aedes aegypti, and Culex pipiens mosquitoes (Diptera: Culicidae) to cool and humid refugium conditions

Like all terrestrial arthropods, mosquitoes must cope with the threat of desiccation. To gain insight into their survival strategies, we recorded the behavioral responses of Anopheles gambiae, Anopheles stephensi, Aedes aegypti, and Culex pipiens offered zones of different microclimatic conditions in laboratory cages. The cooled refugium was at 25.6 degrees C, 86% RH and the control was at 28.5 degrees C, 75% RH, i.e., a difference in saturation deficit of 3.9 mm Hg between the two zones. We show that newly-emerged adults, with no access to water or sugar, prefer the cooler and more humid refugium with a saturation deficit half that in the control and where the mosquitoes could reduce their metabolic rate. This response is delayed in Ae. aegypti, perhaps because the energy reserves accumulated as larvae are higher in this species. This study shows that mosquitoes under stress can use their thermohygroreceptor cells to guide them to locations that facilitate survival.     

Molecular cloning and characterization of the complete acetylcholinesterase gene (Ace1) from the mosquito Aedes aegypti with implications for comparative genome analysis

Insensitive acetylcholinesterase (AChE) has been shown to be responsible for resistance to organophosphates and carbamates in a number of arthropod species. Some arthropod genomes contain a single Ace gene, while others including mosquitoes contain two genes, but only one confers insecticide resistance. Here we report the isolation of the full-length cDNA and characterization of the complete genomic DNA sequence for the Ace1 gene in the yellow fever mosquito, Aedes aegypti. The Ace1 homolog in other mosquito species has been associated with insecticide resistance. The full-length cDNA consists of 2721bp and contains a 2109bp open reading frame that encodes a 702 amino acid protein. The amino acid sequence is highly conserved with that of other mosquitoes, including greater than 90% identity with Culex spp. and about 80% identity with Anopheles gambiae. The genomic DNA sequence includes 138,970bp and consists of eight exons with seven introns ranging from 59 to 114,350bp. Exons 2 and 8 show reduced amino acid conservation across mosquito species, while exons 3-7 are highly conserved. The Ace1 introns in Ae. aegypti reflect a high frequency of repetitive sequences that comprise about 45% of the total intron sequence. The Ace1 locus maps to the p-arm of chromosome 3, which corresponds to the orthologous genome regions in Culex spp. and An. gambiae.     

Evolution and horizontal transfer of a DD37E DNA transposon in mosquitoes

ITmD37E, a unique class II transposable element (TE) with an ancient origin, appears to have been involved in multiple horizontal transfers in mosquitoes as ITmD37E sequences from 10 mosquito species of five genera share high nucleotide (nt) identities. For example, ITmD37E sequences from Aedes aegypti and Anopheles gambiae, which have an estimated common ancestor of 145-200 million years ago, display 92% nt identity. The comparison of ITmD37E and host mosquito phylogenies shows a lack of congruence. The wide distribution of conserved ITmD37Es in mosquitoes and the presence of intact copies suggest that this element may have been recently active.