Behavioral responses of Aedes aegypti,Aedes albopictus,Culex quinquefasciatus,and Anopheles minimus against various synthetic and natural repellent compounds

The behavioral responses of colony populations of Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, and Anopheles minimus to four essential oils (citronella, hairy basil, catnip, and vetiver), two standard repellents (DEET and picaridin), and two synthetic pyrethroids (deltamethrin and permethrin) were conducted in the laboratory using an excito‐repellency test system. Results revealed that Cx. quinquefasciatus and An. minimus exhibited much stronger behavioral responses to all test compounds (65–98% escape for contact, 21.4–94.4% escape for non‐contact) compared to Ae. aegypti (3.7–72.2% escape (contact), 0–31.7% (non‐contact)) and Ae. albopictus (3.5–94.4% escape (contact), 11.2–63.7% (non‐contact)). In brief, essential oil from vetiver elicited the greatest irritant responses in Cx. quinquefasciatus (96.6%) and An. minimus (96.5%) compared to the other compounds tested. The synthetic pyrethroids caused a stronger contact irritant response (65–97.8% escape) than non‐contact repellents (0–50.8% escape for non‐contact) across all four mosquito species. Picaridin had the least effect on all mosquito species. Findings from the current study continue to support the screening of essential oils from various plant sources for protective properties against field mosquitoes.     

Synergistic repellent and irritant effect of combined essential oils on Aedes aegypti (L.) mosquitoes

This study was designed to compare the behavioral responses of Aedes aegypti to a single essential oil and to a mixture of two or three essential oils using an excito‐repellency test chamber. Mixtures were prepared from essential oils extracted from Litsea cubeba (LC), Litsea salicifolia (LS), and Melaleuca leucadendron (ML). In general, the mixture of essential oils produced a much stronger escape response by Ae. aegypti, regardless of the test conditions. No significant difference in escape responses was seen when the mixture of oils was compared with a standard commercial product containing DEET. Greater contact irritancy was seen from mixed oils of LC and LS than with other mixed oils. Mixtures of LC and LS at 0.075% showed the highest synergistic action (65.5% escaped) compared to that with unmixed oil alone at the same concentration (LC/20% and LS=32.2%). In addition, mixtures of LC and LS at 0.075% demonstrated the highest non‐contact repellency (62.7%) and showed a greater effect than the use of LC (20%) or LS (20.3%) alone. We conclude that mixtures of two essential oils show potential as active ingredients for mosquito repellents.     

Spatial repellency and other effects of transfluthrin and linalool on Aedes aegypti and Aedes albopictus

In the present study, the effects of two spatial repellents (SR) were determined for Aedes aegypti and Ae albopictus, the main vectors of dengue, Chikungunya, and Zika fever. The modular high‐throughput screening system (HITSS ) was used to evaluate the response of both species to transfluthrin and linalool SR at different concentrations. The highest spatial repellency results for Ae. aegypti were obtained by transfluthrin to 0.001% with 37.50 ± 4.33%, and for linalool to 10% with 77.50 ± 3.90%. For Ae. albopictus, the highest spatial repellency percentages for transfluthrin 0.01% were 45.00 ± 3.78%, and linalool at 1% and 10% were 56.25 ± 7.06% and 56.25 ± 6.46%, respectively. Transfluthrin caused high levels of mortality with 71.25 ± 6.66%, 79.75 ± 8.65%, and 100% to Ae. aegypti and 70.00 ± 5.98% and 98.75 ± 0.82% to Aedes albopcitus. With the results of this study, we concluded that both the transfluthrin and linalool could be used as protection measures against the bite of Ae. aegypti and Ae. albopictus in the integral strategies for the control of vectors in Mexico.     

Chemistry matters: biological activity of Eucalyptus essential oils on mosquito larval mortality

The mosquito Aedes aegypti L. (Diptera: Culicidae) is a vector of arboviral diseases such as dengue fever. Currently, the main approach to mosquito control is the application of synthetic insecticides, which can lead to negative environmental impacts and insecticide resistance in mosquito populations. As such, there has been increased interest in developing alternative methods for control of vector populations such as utilizing plant compounds that act as larvicides. The aim of this work is to evaluate the effectiveness of Eucalyptus sp. (Myrtaceae) essential oils for control of Ae. aegypti larvae. The essential oils of seven Eucalyptus species and hybrids were extracted by hydrodistillation and analyzed by gas chromatography coupled to mass spectrometry. The essential oils were further diluted in water with acetone (0.40%) at the following concentrations: 100, 50, 25, and 10 μg ml⁻¹. Mortality trials were conducted in plastic containers with a solution of ultrapure water and 200 μl of diluted oil for a total volume of 50 ml per treatment. The experiments for each Eucalyptus species/hybrid and concentration were performed in triplicate, using a control containing only water and acetone. Twenty larvae were added to each container and mortality was recorded at 1, 2, 4, and 24 h. The Eucalyptus essential oils showed larvicidal activity in most of the evaluated concentrations, mainly at 50 and 100 μg ml⁻¹. Eucalyptus benthamii Maiden & Cambage and the hybrid Urograndis displayed the highest larvicidal potential (100% at 24 h) in the 100 μg ml⁻¹ treatment. Larval mortality of Ae. aegypti showed a positive correlation with the compounds γ-, o-cymol, o-cymene, terpineol, 3-dodecylfuran-2,5-dione, α-pinene, globulol, and ledol. The most abundant compounds identified in the essential oils were 1,8-cineole and α-pinene. These results highlight the potential of using Eucalyptus essential oils for the isolation of natural larvicidal products.     

Excito‐repellency of essential oils against an Aedes aegypti (L.) field population in Thailand

An investigation of the behavioral responses of Aedes aegypti (= Stegomyia aegypti) to various concentrations of essential oils (2.5, 5, and 10%) extracted from hairy basil (Ocimum americanum Linn), ginger (Zingiber officinale Roscoe), lemongrass (Cymbopogon citratus Stapf), citronella grass (Cymbopogon nardus Rendle), and plai (Zingiber cassumunar Roxb) were performed using an excito‐repellency test chamber. Results showed that Ae. aegypti exhibited varying levels of escape response in both the contact and noncontact chambers in response to different essential oils. The magnitude of the behaviors changed in a dose‐response fashion depending on the percent volume to volume concentration of oil used. A 2.5% concentration of hairy basil oil produced a significantly greater escape response compared to the other extracts at the same concentration (P< 0.05). Oils of ginger, lemongrass, and citronella produced stronger irritant and repellent responses at the median 5% concentration compared to the lowest and highest concentrations. There was marked suppression of escape for both contact and noncontact tests using 10% concentrations of hairy basil, lemongrass, and citronella, with high knockdown for all three oils after 30 min. Hairy basil and lemongrass had the highest insecticidal activity to Ae. aegypti, with LC₅₀ values of 6.3 and 6.7 percent, respectively. We conclude that the essential oils from native plants tested, and likely many other extracts found in plants, have inherent repellent and irritant qualities that should to be screened and optimized for their behavior‐modifying properties against Ae. aegypti and other biting arthropods of public health and pest importance.     

Chronology of sodium channel mutations associated with pyrethroid resistance in Aedes aegypti

Aedes aegypti is the primary mosquito vector of dengue, yellow fever, Zika and chikungunya. Current strategies to control Ae. aegypti rely heavily on insecticide interventions. Pyrethroids are a major class of insecticides used for mosquito control because of their fast acting, highly insecticidal activities and low mammalian toxicity. However, Ae. aegypti populations around the world have begun to develop resistance to pyrethroids. So far, more than a dozen mutations in the sodium channel gene have been reported to be associated with pyrethroid resistance in Ae. aegypti. Co-occurrence of resistance-associated mutations is common in pyrethroid-resistant Ae. aegypti populations. As global use of pyrethroids in mosquito control continues, new pyrethroid-resistant mutations keep emerging. In this microreview, we compile pyrethroid resistance-associated mutations in Ae. aegypti in a chronological order, as they were reported, and summarize findings from functional evaluation of these mutations in an in vitro sodium channel expression system. We hope that the information will be useful for tracing possible evolution of pyrethroid resistance in this important human disease vector, in addition to the development of methods for global monitoring and management of pyrethroid resistance in Ae. aegypti.     

Laboratory Evaluation of Controlled-release Repellent Treated Pulp Fabric on Human Volunteers Against Mosquito Vectors

Three controlled‐release personal‐use pulp fabric impregnated insect repellent formulations of 5% N, N‐diethyl‐3‐methylbenzamide (DEET), and 10% and 15% neem oils were evaluated in an environmental chamber on volunteers for their repellent efficacy against three mosquito species, Culex pipiens pallens, Aedes aegypti and Ochlerotatus togoi. The 5% DEET formulation showed significant repellency in pulp fabric (5 mm in width) against Culex pipiens pallens and Aedes aegypti (P < 0.05), providing an average repellency of 88.0%, 66.3%, and 46.8% of Cx. pipiens pallens, Ae. Aegypti and O. togoi bites, respectively, during the 6 hours of exposure period. Against night‐biting mosquitoes Cx. pipiens pallens, the DEET formulation provided mostly complete protection for at least 4 hours after the application. In pulp fabric of 10 mm in width, the 5% deet formulation showed significantly the highest repellency among the repellents against O. togoi (P<0.05), providing an average repellency of 52.3% during the 6 hours of exposure period. However, the pulp fabrics treated with 10% and 15% neem oil were less effective than 5% DEET against three mosquito species. This study demonstrated the potential of 5% DEET as pulp fabric repellent against both day‐ and night‐biting mosquitoes.     

Environmentally-Friendly Pesticidal Activities of Callicarpa and Karomia Essential Oils from Vietnam and Their Microemulsions

There is an ongoing interest to identify alternative pesticidal agents to avoid the chronic problems associated with synthetic pesticides. Essential oils have shown promise as botanical pest control agents. In the present study, the essential oils of four members of the Lamiaceae (Callicarpa candicans, C. erioclona, C. macrophylla, and Karomia fragrans; Vietnamese names: Nàng nàng, Tu châu lông mem, Tu châu lá to and Cà diện, respectively), obtained from wild populations in Vietnam, have been obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry. The essential oils were formulated into microemulsions and the essential oils and their microemulsions were screened for mosquito larvicidal activity against Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, and for molluscicidal activity against Pomacea canaliculata. Atractylone and (E)-caryophyllene dominated the volatiles of C. candicans (CCEO) and C. erioclona (CEEO), while the major component in C. macrophylla (CMEO) and K. fragrans (KFEO) was (E)-caryophyllene. The essential oils and microemulsions of both C. candicans and C. erioclona exhibited excellent larvicidal activity against all three mosquito species (Ae. aegypti, Ae. albopictus, and Cx. quinquefasciatus) with LC₅₀ values <10 μg/mL. Additionally, the larvicidal activity of the microemulsions were significantly improved compared with their free essential oils, especially for C. candicans and C. erioclona. All four essential oils and their microemulsions showed excellent molluscicidal activity with LC₅₀ <10 μg/mL. In most cases, the essential oils and microemulsions showed greater pesticidal activity against target organisms than the non-target freshwater fish, Oreochromis niloticus. The in silico studies on physicochemical and ADMET properties of the major components in the studied essential oils were also investigated and most of the compounds possessed a favorable ADMET profile. Computational modeling studies of the studied compounds demonstrated a favorable binding interaction with the mosquito odorant-binding protein target and support atractylone, β-selinene, and caryophyllene oxide as potential inhibitors. Based on the observed pesticidal activities of the essential oils and their microemulsions, the Callicarpa species and K. fragrans should be considered for potential cultivation and further exploration as botanical pesticidal agents.     

Evaluation of boric acid as toxic sugar bait against resistant Aedes aegypti mosquitoes

Current methods of broad area application of contact insecticides used in mosquito control are becoming less effective, primarily due to resistance within mosquito populations. New methods that can deliver ingestible insecticides are being investigated as a means to mitigate resistance. This study evaluated insecticide delivery through toxic sugar baits (TSB) and resulting mortality of susceptible and resistant strains of Aedes aegypti. Two Ae. aegypti strains were evaluated using a 1% boric acid TSB: the susceptible Orlando 1952 (ORL) strain and the resistant Puerto Rican (PR) strain. The TSB resulted in high mortality for both ORL and PR strain of Ae. aegypti. Average mortality of female mosquitoes given TSB was 90.8% for PR and 99.3% for ORL. Our study suggests that targeting resistant mosquitoes with ingestible insecticides through TSBs could be a viable alternative to current mosquito control strategies and should be considered when developing an integrated vector management program.     

Contact irritancy and spatial repellency behaviors in Anopheles albimanus Wiedemann (Diptera: Culicidae) collected in Orange Walk,Belize, C.A.

Anopheles albimanus Wiedemann is a vector of malaria in northern Belize. Previous studies have identified behavioral responses in this species when exposed to certain chemicals. We used a high throughput screening system to evaluate the contact irritant and spatial repellency responses exhibited by An. albimanus collected from Orange Walk, Belize, Central America. Anopheles albimanus behavior was significantly altered by a number of key public health insecticides. Significant irritant responses to alphacypermethrin, deltamethrin, permethrin, DDT, and propoxur were recorded, while spatial repellency responses were only elicited by DDT. Malathion resulted in neither a contact irritant or spatial repellency response. These results are in congruence with behavioral patterns previously observed for An. albimanus and for Aedes aegypti in the same system. This study produced baseline data on the behaviors of An. albimanus and confirms that the majority of compounds used as indoor residual sprays may induce premature exiting by An. albimanus in addition to killing the mosquito. This effect would decrease contact with humans and thus disrupt malaria transmission.     

Maintenance of mosquito vectors: effects of blood source on feeding,survival, fecundity,and egg hatching rates

Artificial membrane‐feeding techniques have replaced direct feeding on animals for the maintenance of malaria and arbovirus vectors in many laboratories. Membrane feeding facilitates controlled experimentation of pathogen transmission during mosquito feeding. Sheep blood is commonly used due to its availability and low cost. We evaluated the impact of blood source (human, guinea pig, sheep, and hamster via direct feeding) on feeding rates, adult survival, fecundity, hatching rates, and developmental times for five species of laboratory‐colonized mosquitoes (Anopheles dirus, An. cracens, An. minimus, An. sawadwongporni, and Ae. aegypti). We found that feeding rates differ among blood sources within mosquito species. Survival, fecundity, and hatching rates were lower in all Anopheles species and Ae. aegypti after membrane feeding on sheep blood. Survival rates seven days post‐feeding on sheep blood were significantly lower (P<0.05) for An. dirus (84.2%), An. minimus (67.2%), An. sawadwongporni (51.5%), and An. cracens (35.5%) relative to other blood sources. An. minimus and An. sawadwongporni laid no eggs by seven days post‐feeding with sheep blood, while An. dirus and An. cracens produced significantly fewer numbers of eggs and demonstrated significantly lower hatching rates relative to what was observed with the other blood sources. These findings support the conclusion that sheep blood is not a suitable blood source for laboratory rearing of Anopheles spp.     

Electrophysiological and behavioural response of Aedes albopictus to n‐heinecosane,an ovipositional pheromone of Aedes aegypti

Aedes aegypti (L.) and Aedes albopictus (Skuse) (Diptera: Culicidae) are highly anthropophilic mosquito species and potential vectors of dengue and yellow fever. The location of suitable sites for oviposition requires a set of visual, tactile, and olfactory cues that influence females before they lay their eggs. In this study, the effect of n‐heneicosane, a recognized oviposition pheromone of Ae. aegypti, on the olfactory receptors of the antennae of Ae. aegypti and Ae. albopictus was studied using electroantennographic detection coupled to gas chromatography (GC‐EAD). A significant electroantennographic response to n‐heneicosane in adult females of both mosquito species was observed. In addition, gravid Ae. albopictus females laid more eggs in substrate treated with n‐heneicosane at 0.1, 1, or 10 p.p.m. than in the control, denoting oviposition attractancy. Conversely, at 30, 50, 100, and 200 p.p.m., more eggs were laid in the control substrate, indicating oviposition repellency. Analysis of the larval cuticle by GC and mass spectrometry confirmed the presence of n‐heneicosane in the cuticles of Ae. albopictus larvae. The species‐specific role of n‐heneicosane as an oviposition pheromone in Ae. aegypti and its significance as a behaviour modifier of Ae. albopictus in breeding sites is discussed.     

Co-occurrence Patterns of the Dengue Vector Aedes aegypti and Aedes mediovitattus, a Dengue Competent Mosquito in Puerto Rico

Aedes aegypti is implicated in dengue transmission in tropical and subtropical urban areas around the world. Ae. aegypti populations are controlled through integrative vector management. However, the efficacy of vector control may be undermined by the presence of alternative, competent species. In Puerto Rico, a native mosquito, Ae. mediovittatus, is a competent dengue vector in laboratory settings and spatially overlaps with Ae. aegypti. It has been proposed that Ae. mediovittatus may act as a dengue reservoir during inter-epidemic periods, perpetuating endemic dengue transmission in rural Puerto Rico. Dengue transmission dynamics may therefore be influenced by the spatial overlap of Ae. mediovittatus, Ae. aegypti, dengue viruses, and humans. We take a landscape epidemiology approach to examine the association between landscape composition and configuration and the distribution of each of these Aedes species and their co-occurrence. We used remotely sensed imagery from a newly launched satellite to map landscape features at very high spatial resolution. We found that the distribution of Ae. aegypti is positively predicted by urban density and by the number of tree patches, Ae. mediovittatus is positively predicted by the number of tree patches, but negatively predicted by large contiguous urban areas, and both species are predicted by urban density and the number of tree patches. This analysis provides evidence that landscape composition and configuration is a surrogate for mosquito community composition, and suggests that mapping landscape structure can be used to inform vector control efforts as well as to inform urban planning.     

Genetic evidence for the origin of Aedes aegypti,the yellow fever mosquito,in the southwestern Indian Ocean

Aedes aegypti is among the best‐studied mosquitoes due to its critical role as a vector of human pathogens and ease of laboratory rearing. Until now, this species was thought to have originated in continental Africa, and subsequently colonized much of the world following the establishment of global trade routes. However, populations of this mosquito on the islands in the southwestern Indian Ocean (SWIO), where the species occurs with its nearest relatives referred to as the Aegypti Group, have received little study. We re‐evaluated the evolutionary history of Ae. aegypti and these relatives, using three data sets: nucleotide sequence data, 18,489 SNPs and 12 microsatellites. We found that: (a) the Aegypti Group diverged 16 MYA (95% HPD: 7–28 MYA) from its nearest African/Asian ancestor; (b) SWIO populations of Ae. aegypti are basal to continental African populations; (c) after diverging 7 MYA (95% HPD: 4–15 MYA) from its nearest formally described relative (Ae. mascarensis), Ae. aegypti moved to continental Africa less than 85,000 years ago, where it recently (<1,000 years ago) split into two recognized subspecies Ae. aegypti formosus and a human commensal, Ae. aegypti aegypti; (d) the Madagascar samples form a clade more distant from all other Ae. aegypti than the named species Ae. mascarensis, implying that Madagascar may harbour a new cryptic species; and (e) there is evidence of introgression between Ae. mascarensis and Ae. aegypti on Réunion, and between the two subspecies elsewhere in the SWIO, a likely consequence of recent introductions of domestic Ae. aegypti aegypti from Asia.     

Structure–Activity Relationship Studies on Derivatives of Eudesmanolides from Inula helenium as Toxicants against Aedes aegypti Larvae and Adults

An Aedes aegypti larval toxicity bioassay was performed on compounds representing many classes of natural compounds including polyacetylenes, phytosterols, flavonoids, sesquiterpenoids, and triterpenoids. Among these compounds, two eudesmanolides, alantolactone, and isoalantolactone showed larvicidal activities against Ae. aegypti and, therefore, were chosen for further structure–activity relationship study. In this study, structural modifications were performed on both alantolactone and isoalantolactone in an effort to understand the functional groups necessary for maintaining and/or increasing its activity, and to possibly lead to more effective insect‐control agents. All parent compounds and synthetic modification reaction products were evaluated for their toxic activities against Ae. aegypti larvae and adults. Structure modifications included epoxidations, reductions, catalytic hydrogenations, and Michael additions to the α,β‐unsaturated lactones. None of the synthetic isomers synthesized and screened against Ae. aegypti larvae were more active than isoalantolactone itself which had an LC₅₀ value of 10.0 μg/ml. This was not the case for analogs of alantolactone for which many of the analogs had larvicidal activities ranging from 12.4 to 69.9 μg/ml. In general, activity trends observed from Ae. aegypti larval screening were not consistent with observations from adulticidal screening. The propylamine Michael addition analog of alantolactone was the most active adulticide synthesized with an LC₅₀ value of 1.07 μg/mosquito. In addition, the crystal structures of both alantolactone and isoalantolactone were determined using CuK_α radiation, which allowed their absolute configurations to be determined based on resonant scattering of the light atoms.     

Frequency of pyrethroid resistance in Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Thailand

Thirty‐two Aedes aegypti populations collected throughout Thailand and five populations of Aedes albopictus from southern Thailand were subjected to standard WHO contact bioassays to assess susceptibility to three commonly used synthetic pyrethroids: permethrin, deltamethrin, and lambda‐cyhalothrin. A wide degree of physiological response to permethrin was detected in Ae. aegypti, ranging from 56.5% survival (Lampang, northern Thailand) to only 4% (Kalasin in northeastern and Phuket in southern Thailand). All 32 populations of Ae. aegypti were found to have evidence of incipient resistance (62.5%) or levels of survival deemed resistant (37.5%) to permethrin. Four populations of Ae. albopictus were found with incipient resistance (97 – 80% mortality) and one with resistance (< 80%) to permethrin. The majority of Ae. aegypti populations (68.7%) was susceptible (> 98% mortality) to deltamethrin, with incipient resistance (observed 97–82% mortality) in other localities. In contrast, all populations of Ae. aegypti were completely susceptible (100% mortality) to the recommended operational dosage of lambda‐cyhalothrin. All five populations of Ae. albopictus were found completely susceptible to both deltamethrin and lambda‐cyhalothrin. Evidence of defined incipient or resistance to synthetic pyrethroids mandates appropriate response and countermeasures to mitigate further development and spread of resistance. In light of these findings, we conclude that routine and comprehensive susceptibility monitoring of dengue mosquito vectors to synthetic pyrethroids should be a required component of resistance management policies and disease control activities.     

Pre‐treatment of Stegomyia aegypti mosquitoes with a sublethal dose of imidacloprid impairs behavioural avoidance induced by lemon oil and DEET

The present study was conducted to determine whether imidacloprid can impair the avoidance behaviour of the mosquito Stegomyia aegypti. Laboratory investigations using a T‐maze apparatus showed that St. aegypti mosquitoes present long term avoidance behaviour when they are exposed to repetitive trials with lemon oil and DEET. The present study tested the effect of a sublethal dose of imidacloprid on the avoidance behaviour of St. aegypti mosquitoes over a 48 h period. Data suggest that 0.5 ng of imidacloprid/mosquito reduces the avoidance behaviour of mosquitoes exposed to lemon oil, on the first day of exposure, after the second trial; whereas imidacloprid affected DEET repellency only the first day of exposure, after the second trial. Imidacloprid was toxic against St. aegypti mosquitoes, and at sublethal doses was able to impair the repellency induced by lemon oil and DEET. The present data were consistent with the finding that St. aegypti mosquitoes exhibit long term avoidance behaviour, and treatment of mosquitoes with a sublethal dose of imidacloprid under DEET application can affect the repellency of DEET against St. aegypti.     

Aedes species in treeholes and fruit husks between dry and wet seasons in southeastern Senegal

During the dry season in February, 2010 and the wet season in September, 2011 we sampled mosquito larvae and eggs from treeholes of seven native hardwood species and the husks of Saba senegalensis in 18 sites in the PK‐10 forest in southeastern Senegal. Larvae were reared to adults for species identification. In the dry season, we recovered 408 Aedes mosquitoes belonging to seven species. Aedes aegypti s.l. comprised 42.4% of the collection, followed by Ae. unilineatus (39%). In contrast to reports from East Africa, both Ae. aegypti aegypti and Ae. aegypti formosus were recovered, suggesting that both subspecies survive the dry season in natural larval habitats in West Africa. In the wet season, 455 mosquitoes were collected but 310 (68.1%) were the facultatively predaceous mosquito Eretmapodites chrysogaster. The remaining 145 mosquitoes consisted of ten Aedes species. Aedes aegypti s.l. comprised 55.1% of these, followed by Ae. apicoargenteus (15.2%) and Ae. cozi (11.7%). Similar to East Africa, most (90%) of Ae. aegypti s.l. in the wet season were subspecies formosus.     

Lantana camara Essential Oils from Vietnam: Chemical Composition,Molluscicidal, and Mosquito Larvicidal Activity

Lantana camara is a troublesome invasive plant introduced to many tropical regions, including Southeast Asia. However, the plant does hold promise as a source of essential oils that may be explored for potential use. Fresh water snails such as Pomacea canaliculata, Gyraulus convexiusculus, and Tarebia granifera can be problematic agricultural pests as well as hosts for parasitic worms. Aedes and Culex mosquitoes are notorious vectors of numerous viral pathogens. Control of these vectors is of utmost importance. In this work, the essential oil compositions, molluscicidal, and mosquito larvicidal activities of four collections of L. camara from north-central Vietnam have been investigated. The sesquiterpene-rich L. camara essential oils showed wide variation in their compositions, not only compared to essential oils from other geographical locations (at least six possible chemotypes), but also between the four samples from Vietnam. L. camara essential oils showed molluscicidal activities comparable to the positive control, tea saponin, as well as other botanical agents. The median lethal concentrations (LC₅₀) against the snails were 23.6–40.2 μg/mL (P. canaliculata), 7.9–29.6 μg/mL (G. convexiusculus), and 15.0–29.6 μg/mL (T. granifera). The essential oils showed good mosquito larvicidal activities with 24-h LC₅₀ values of 15.1–29.0 μg/mL, 26.4–53.8 μg/mL, and 20.8–59.3 μg/mL against Ae. aegypti, Ae. albopictus, and Cx. quinquefasciatus, respectively. The essential oils were more toxic to snails and mosquito larvae than they were to the non-target water bug, Diplonychus rusticus (24-h LC₅₀=103.7–162.5 μg/mL). Sesquiterpene components of the essential oils may be acting as acetylcholinesterase (AChE) inhibitors. These results suggest that the invasive plant, L. camara, may be a renewable botanical pesticidal agent.     

Making generalizations about vectors: Is there a physiology of “the mosquito”?

Many of the generalizations made about mosquito behavior and physiology are based on the extensive research on the yellow fever mosquito, Aedes aegypti (L.). However, sufficient differences exist among the numerous species of mosquitoes that make many of these generalizations unwarranted. Some of the specific differences between Ae. aegypti and other mosquito species, particularly the important malaria vector Anopheles gambiae, are discussed.