N-substituted methyl maleamates as larvicidal compounds against Aedes aegypti (Diptera: Culicidae)

Parasitology Research - Severe human arboviral diseases can be transmitted by the mosquito Aedes aegypti (L.), including dengue, chikungunya, zika, and yellow fever. The use of larvicides in...     

Utilization of human blood and sugar as nutrients by female Aedes aegypti (Diptera: Culicidae)

We examined the utilization of sugar and human blood as nutrient sources for small and large female Aedes aegypti (L.) when they were fed blood 2 or 5 d after emergence. Laboratory-reared mosquitoes were fed human blood alone or sugar plus human blood and assayed at 4, 12, 24, and 48 h after the blood meal. Starved and well-fed mosquitoes were obtained by holding teneral females (< or = 1 d old) with 0, 5, 10, and 15% sucrose solutions ad libidum from emergence. Both small and large mosquitoes increased their glycogen and sugar levels significantly by feeding on blood only or on blood plus sugar when they imbibed a human blood meal on day 2 after emergence. Mosquitoes only fed blood on day 2 had the highest lipid levels of any treatment group. Both size classes and all feeding regimes failed to increase the total amount of glycogen, lipid, or sugar when they fed on blood 5 d after emergence. We conclude that there is an energetic advantage to Ae. aegypti when they feed on blood early in adult life (< or = day 2 after emergence).     

Knockdown and larvicidal activity of six monoterpenes against Aedes aegypti (Diptera: Culicidae) and their structure-activity relationships

The relationships between physicochemical parameters of majority components of Eucalyptus essential oils and their insecticide effect were evaluated on Aedes aegypti (L.) (Diptera: Culicidae). The octanol–water partition coefficients of the monoterpenes were estimated by the atom/fragment contribution method and the vapor pressures were determined by our laboratory in previous studies. The larvicidal activity (LC_{50 (ppm)}) and knockdown effect (KT_{50 (min)}) of each component was determined. The results show that the toxicity of EOs main components of Eucalyptus on adults and larvae of A. aegypti is strongly related to their physicochemical properties (vapor pressure and Log P). However, the interaction of both variables (vapor pressure * Log P) explains the toxicological phenomenon more precisely. The regression models were expressed as follows: KT _50(min)?=????10.9?+?3.7?*?Log P?+?1.9?*?1/P_vapor (R²?=?0.80;?F?=?42.5) and LC _50(ppm)?=????94.3?+?438.6?*? 1/Log P?+?2.8?*? 1/P_vapor (F?=?57.8;?R²?=?0.85). The six evaluated components present different functional groups. Therefore, it was considered to evaluate the monoterpenes as a group and separated in two groups: oxygenated monoterpenes (α-terpineol, 4-terpineol, and 1,8-cineole) and terpene hydrocarbons (γ-terpinene, p-cymene, and α-pinene). The results show the regression models for each group as follows: (A) oxygenated terpenes: KT _50(min)?=???515.3?+?1613.2???1/Log P?+?5,?2???1/P_vapor (F?=?3176.7?R²?=?0.99) and LC _50(ppm) ?=????1679.4?+?5402.1???1/Log P?+?12.7??? 1/P_vapor (F?=?282.9;?R²?=?0.99). (B) Hydrocarbons terpenes: KT _50(min)?=?18.2???58.3?*?1/Log P?+?2.7?*?1/P_vapor (F?=?171.7;? R²?=?0.97) and LC _50(ppm)?=???21.1?+?174.9???1/Log P???14.3???1/P_vapor (F?=?410.0;?R²?=?0.99). The association between the toxic effect of the evaluated monoterpenes against A. aegypti and the physicochemical properties can be better described when they are separated into functional groups (hydrocarbons vs. oxygenated terpenes).     

Aedes aegypti (Diptera: Culicidae) age determination by cuticular hydrocarbon analysis of female legs

We previously described methods for age-grading female Aedes aegypti (L.) by gas chromatographic (GC) analysis of whole-body cuticular hydrocarbon patterns. Two regression models were developed that were based on the age-dependent, relative abundance of 2 cuticular hydrocarbons, pentacosane (GC peak 1) and nonacosane (GC peak 5). We have refined this method so that only the legs are required to age individual females. Two new regression models were developed that also use the relative abundance of a 3rd cuticular hydrocarbon, octacosane (GC peak 4). These models improve the overall accuracy of the cuticular hydrocarbon method for aging female mosquitoes, especially for older females from 132 to 165 degree-days (DD) of age (12-15 calendar days at 28 degrees C). The correlation coefficients (R2) for the best-fitted linear regression models for aging females from 0 to 132 and 0-165 DD were 0.80 and 0.81, respectively (P < 0.001 in all cases). The use of leg cuticular hydrocarbons for estimating the age of female Ae. aegypti has a significant advantage over whole-body extracts as indicated by the decreased variability associated with the relative abundance of pentacosane and the expanded range over which the models were able to predict age accurately by the addition of the relative abundance of octacosane.     

Invertebrate carcasses as a resource for competing Aedes albopictus and Aedes aegypti (Diptera: Culicidae)

Terrestrial invertebrate carcasses are an important resource for insects developing in pitcher plants. However, little is known of the role of these carcasses in other containers, which also receive leaf fall and stemflow inputs. This experiment investigated effects of accumulated invertebrate carcasses as a resource for two competing mosquitoes, Aedes albopictus (Skuse) and Aedes aegypti (L.), whether either species differentially benefited from accumulated carcasses, and if such a benefit affected interspecific competition. First, we measured accumulation of invertebrate carcasses in standard containers at a field site. We then used a replacement series with five different species ratios at the same total density, and varied the input of invertebrate carcasses [dead Drosophila melanogaster (Meigen) ] in three levels: none, the average input from our field site, or the maximum input recorded at our field site. Survivorship, development time, and mass were measured for each mosquito species as correlates of population growth, and were used to calculate a population performance index, lambda'. There were strong positive effects of invertebrate carcass additions on all growth correlates and lambda'. Differences in performance between species were pronounced in small or no carcass additions and absent in large inputs of invertebrate carcasses, but there was little evidence that inputs of invertebrate carcasses altered the competitive advantage in this system. These results suggest that terrestrial invertebrate carcasses may be an important resource for many types of container communities, and large accumulations of dead invertebrates may reduce resource competition between these mosquitoes, thus favoring coexistence. We propose that the total amount of resource, including accumulated invertebrate carcasses, may explain observed patterns of replacement involving these mosquitoes.     

Oral toxicity of Photorhabdus luminescens and Xenorhabdus nematophila (Enterobacteriaceae) against Aedes aegypti (Diptera: Culicidae)

Dengue fever is an important vector-borne disease, mainly transmitted by Aedes aegypti. To date, there are no vaccines or effective drugs available against this arboviral disease. As mosquito control is practically the only method available to control dengue fever, alternative and cost-effective pest control strategies need to be explored. The gram-negative enteric bacteria Xenorhabdus and Photorhabdus are symbiotically associated with nematode parasites, which themselves are highly pathogenic for insect larvae. Here, we evaluate the oral toxicity of these entomopathogenic bacteria in A. aegypti larvae. The susceptibility of larvae (third late or fourth early instars) was assessed by exposing them to suspensions containing Photorhabdus luminescens or Xenorhabdus nematophila, respectively. Two diet treatments were tested with larvae fed on pet food and unfed larvae. After 24 h, larvae began to die when exposed to the bacteria. Exposure to P. luminescens killed 73 % of the fed and 83 % of the unfed larvae, respectively. In comparison, X. nematophila was less pathogenic, killing 52 % of the larvae in the fed and 42 % in the unfed treatment. Remarkably, cannibalism was observed in all bioassays after exposing larvae to either of the bacterial species. To our knowledge, this is the first report demonstrating the efficiency of these entomopathogenic bacteria for oral A. aegypti killing. Our results provide a promising basis for using these bacteria as bioinsecticides for mosquito control in the future.     

Pathogenicity of some hypocrealean fungi to adult Aedes aegypti (Diptera: Culicidae)

The pathogenicity of 19 hypocrealean entomopathogenic fungi from seven different genera in adult Aedes aegypti was tested. All fungi proved to be pathogenic, and Isaria fumosorosea, Lecanicillium muscarium, Lecanicillium psalliotae, Metarhizium anisopliae, Metarhizium lepidiotae, Metarhizium majus, Metarhizium frigidum, Paecilomyces carneus, and Paecilomyces lilacinus caused total mortality within 15 days of exposure of mosquitoes to the fungal culture. All fungi developed on dead individuals. The high susceptibility of adults to most tested strains underlines the interest of entomopathogenic fungi—especially those of the genera Metarhizium, Isaria, Paecilomyces and Lecanicillium—for biological control of A. aegypti.     

Larvicidal activity of Copaifera sp. (Leguminosae) oleoresin microcapsules against Aedes aegypti (Diptera: Culicidae) larvae

Studies have demonstrated the potential of Copaifera sp. oleoresin to control Aedes aegypti proliferation. However, the low water solubility is a factor that limits its applicability. Thus, the micro- or nanoencapsulation could be an alternative to allow its use in larval breeding places. The purpose of this study was to evaluate if achievable lethal concentrations could be obtained from Copaifera sp. oleoresin incorporated into polymers (synthetic or natural) and, mainly, if it can be sustained in the residual activity compared to the pure oil when tested against the A. aegypti larvae. Microcapsules were prepared by the process of emulsification/precipitation using the polymers of cellulose acetate (CA) and poly(ethylene-co-methyl acrylate) (PEMA), yielding four types of microcapsules: MicPEMA₁ and MicPEMA₂, and MicCA₁ and MicCA₂. When using only Copaifera sp. oleoresin, the larvicidal activity was observed at concentrations of LC₅₀ = 48 mg/L and LC₉₉ = 149 mg/L. For MicPEMA₁, the LC₅₀ and LC₉₉ were 78 and 389 mg/L, respectively. Using MicPEMA₂, the LC₅₀ was 120 mg/L and LC₉₉ >500 mg/L. For microcapsules MicCA₁ and MicCA₂, the LC₅₀ and LC₉₉ were 42, 164, 140, and 398 mg/L, respectively. For a dose of 150 mg/L of pure oleoresin, the residual activity remained above 20% for 10 days, while the dose of 400 mg/L remained above 40% for 21 days. The MicPEMA₁ microcapsules showed a loss in residual activity up to the first day; however, it remained in activity above 40% for 17 days. The microcapsules of MicCA₁ showed similar LC₅₀ of pure oil with 150 mg/L.     

Mosquitocidal properties of nereistoxin against Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae)

Emergence of resistance among mosquitoes is a recent problem. Safe and eco-friendly agents from biological origins are the need of the hour. Nereistoxin, a naturally occurring substance, was first isolated from the marine annelid Lumbriconereis heteropoda and stored in the freezer. In the present study, the toxicity of nereistoxin was evaluated against vector mosquitoes. The larvicidal, ovicidal and adulticidal activities of nereistoxin were assayed for their toxicity against three important vector mosquitoes, viz., Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae). The nereistoxin was inversely proportional to the concentration and directly proportional to the mosquitoes. The larvicidal activity after 24 h LC₅₀ value was observed at 0.467, 0.535 and 0.601 ppm for A. stephensi, A. aegypti and C. quinquefasciatus, respectively. The ovicidal activity after 120 h zero percentage of egg hatchability was observed at a concentration of 0.8 ppm for A. stephensi and 1.0 ppm for A. aegypti and C. quinquefasciatus. The results of the adulticidal activity after 24 h LD₅₀ value were observed at 0.022, 0.028 and 0.034 ppm for A. stephensi, A. aegypti and C. quinquefasciatus, respectively. The extracted nereistoxin was characterized and identified by ultraviolet, infrared, nuclear magnetic resonance, mass spectroscopic methods and high pressure liquid chromatography. These results clearly reveal that the nereistoxin served as a potential larvicidal, ovicidal and adulticidal activity against vector mosquitoes.     

Wing shape as an indicator of larval rearing conditions for Aedes albopictus and Aedes aegypti (Diptera: Culicidae)

Estimating a mosquito's vector competence, or likelihood of transmitting disease, if it takes an infectious bloodmeal, is an important aspect of predicting when and where outbreaks of infectious diseases will occur. Vector competence can be affected by rearing temperature and inter- and intraspecific competition experienced by the individual mosquito during its larval development. This research investigates whether a new morphological indicator of larval rearing conditions, wing shape, can be used to distinguish reliably temperature and competitive conditions experienced during larval stages. Aedes albopictus (Skuse) and Aedes aegypti (L.) (Diptera: Culicidae) larvae were reared in low intraspecific, high intraspecific, or high interspecific competition treatments at either 22 or 32 degrees C. The right wing of each dried female was removed and photographed. Nineteen landmarks and 20 semilandmarks were digitized on each wing. Shape variables were calculated using geometric morphometric software. Canonical variate analysis, randomization multivariate analysis of variance, and visualization of landmark movement using deformation grids provided evidence that although semilandmark position was significantly affected by larval competition and temperature for both species, the differences in position did not translate into differences in wing shape, as shown in deformation grids. Two classification procedures yielded success rates of 26 - 49%. Accounting for wing size produced no increase in classification success. There seemed to be a significant relationship between shape and size. These results, particularly the low success rate of classification based on wing shape, show that shape is unlikely to be a reliable indicator of larval rearing competition and temperature conditions for Ae. albopictus and Ae. aegypti.     

Myco-synthesis of silver nanoparticles using Beauveria bassiana against dengue vector,Aedes aegypti (Diptera: Culicidae)

The efficacy of silver synthesized biolarvicide with the help of entomopathogenic fungus, Beauveria bassiana, was assessed against the different larval instars of dengue vector, Aedes aegypti. The silver nanoparticles were observed and characterized by a scanning electron microscope (SEM) and energy-dispersive X-ray (EDX). A surface plasmon resonance band was observed at 420 nm in UV-vis spectrophotometer. The characterization was confirmed by shape (spherical), size 36.88–60.93 nm, and EDX spectral peak at 3 keV of silver nanoparticles. The synthesized silver nanoparticles have been tested against the different larval instars of Ae. aegypti at different concentrations for a period of 24 h. Ae. aegypti larvae were found more susceptible to the synthesized silver nanoparticles. The LC₅₀ and LC₉₀ values are 0.79 and 1.09 ppm with respect to the Ae. aegypti treated with B. bassiana (Bb) silver nanoparticles (AgNPs). First and second instar larvae of Ae. aegypti have shown cent percent mortality while third and fourth instars found 50.0, 56.6, 70.0, 80.0, and 86.6 and 52.4, 60.0, 68.5, 76.0, and 83.3 % mortality at 24 h of exposure in 0.06 and 1.00 ppm, respectively. It is suggested that the entomopathogenic fungus synthesized silver nanoparticles would be appropriate for environmentally safer and greener approach for new leeway in vector control strategy through a biological process.     

Biosynthesis of silver nanoparticles using Bacillus thuringiensis against dengue vector, Aedes aegypti (Diptera: Culicidae)

The present study reveals the larvicidal activity of silver nanoparticles (AgNPs) synthesized by Bacillus thuringiensis (Bt) against Aedes aegypti responsible for the diseases of public health importance. The Bt-AgNPs were characterized by using UV–visible spectrophotometer followed by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. A surface plasmon resonance spectrum of AgNps was obtained at 420 nm. The particle sizes were measured through SEM imaging ranging from 43.52 to 142.97 nm. The Bt-AgNPs has also given a characteristic peak at 3 keV in EDX image. Interestingly, the mortality rendered by Bt-AgNPs was comparatively high than that of the control against third-instar larvae of A. aegypti (LC₅₀ 0.10 ppm and LC₉₀ 0.39 ppm) in all the tested concentrations, viz. 0.03, 0.06, 0.09, 0.12, and 0.15 ppm. Hence, Bt-AgNPs would be significantly used as a potent mosquito larvicide against A. aegypti.     

Larvicidal activity of saponin from Achyranthes aspera against Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae)

The acetone, chloroform, ethyl acetate, hexane and methanol leaf extracts of Acalypha indica, Achyranthes aspera, Leucas aspera, Morinda tinctoria and Ocimum sanctum were studied against the early fourth-instar larvae of Aedes aegypti L and Culex quinquefasciatus Say. The larval mortality was observed after 24 h exposure. All extracts showed moderate larvicidal effects; however, the highest larval mortality was found in the ethyl acetate extract of A. aspera. In the present study, bioassay-guided fractionation of A. aspera led to the separation and identification of a saponin as a potential mosquito larvicidal compound, with LC₅₀ value of 18.20 and 27.24 ppm against A. aegypti and C. quinquefasciatus, respectively. ¹H NMR, ¹³C NMR and mass spectral data confirmed the identification of the active compound. This is the first report on the mosquito larvicidal activity of the saponin from the ethyl acetate extract of A. aspera. This study investigates the potential of crude extracts from commonly used medical herbs in India as an environmentally safe measure to control the vector of dengue and lymphatic filariasis.     

Larvicidal activity of some Euphorbiaceae plant extracts against Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae)

Larvicidal activity of ethyl acetate, butanol, and petroleum ether extracts of five species of Euphorbiaceae plants, Jatropha curcas, Pedilanthus tithymaloides, Phyllanthus amarus, Euphorbia hirta, and Euphorbia tirucalli, were tested against the early fourth instar larvae of Aedes aegypti L. and Culex quinquefasciatus (Say). The larval mortality was observed after 24 h of exposure. All extracts showed low larvicidal effects; however, the highest larval mortality was found in petroleum ether extract. The LC₅₀ value of petroleum ether extracts of J. curcas, P. tithymaloides, P. amarus, E. hirta, and E. tirucalli were 8.79, 55.26, 90.92, 272.36, and 4.25 ppm, respectively, against A. aegypti and 11.34, 76.61, 113.40, 424.94, and 5.52 ppm, respectively, against C quinquefasciatus. Of the various ratios tested, the petroleum ether extracts of J. curcas and E. tirucalli were observed to be more efficient than the other plant extracts. It is, therefore, suggested that E. tirucalli can be applied as an ideal potential larvicide against A. aegypti and C. quinquefasciatus. This is an ideal ecofriendly approach for the control of the dengue vector, A. aegypti, and the lymphatic filariasis vector, C. quinquefasciatus.     

Vertebrate hosts of Aedes aegypti and Aedes mediovittatus (Diptera: Culicidae) in rural Puerto Rico

The distribution of Aedes (Stegomyia) aegypti (L.), the main vector of dengue viruses (DENV) worldwide, overlaps with Aedes (Gymnometopa) mediovittatus (Coquillett), the Caribbean treehole mosquito, in urban, suburban, and rural areas. Ae. mediovittatus is a competent vector of DENV with high rates of vertical DENV transmission in the laboratory. This study determined whether Ae. mediovittatus feeds on humans and compared its feeding patterns with co-occurring Ae. aegypti in two rural communities of Puerto Rico. Adult mosquitoes were captured for three consecutive days every week from July 2009 to May 2010 using BG-Sentinel traps with skin lures that were placed in the front yard of houses in both communities. Three methods were used to identify the 756 bloodmeals obtained in this study: a multiplex polymerase chain reaction (PCR) for humans and dogs targeting cytochrome b; a PCR targeting the 16S rRNA; and a nested PCR targeting cytochrome b. Ae. mediovittatus fed mostly on humans (45-52%) and dogs (28-32%) but also on cats, cows, horses, rats, pigs, goats, sheep, and chickens. Ae. aegypti fed mostly on humans (76-79%) and dogs (18-21%) but also on cats, horses, and chickens. Our results indicate that Ae. mediovittatus may have a relatively high rate of vector-human contact, which might facilitate virus transmission or harborage in rural areas of Puerto Rico.