Insect Growth Regulator (IGR) novaluron is an alternative to synthetic neuro-inhibitory insecticides. Present study was designed to assess appropriate dosages of novaluron for dengue vector control. ...Larvae of Aedes aegypti and Ae. albopictus were exposed to a concentration series of novaluron (Rimon EC10) for two fixed exposure periods of 7-days and 14-days to determined LC
and LC
values. Inhibition of adult emergence (IE
and IE
) was determined by a 14-day exposure. Semi-field experiments were conducted by exposing cohorts of Ae. aegypti larvae to IE
, 2 × IE
and 10 × IE
novaluron concentrations in water storage buckets (10 L) and plastic barrels (200 L). For the 7-day exposure, LC
values were 0.047-0.049 ppm and LC
were 0.144-0.151 ppm. For 14-day exposure, these values were 0.002-0.005 ppm and 0.006-0.01 ppm respectively. For both species, IE
was 0.001 ppb under semi-field conditions, and was effective for nearly 2 months. Novaluron concentration 0.01 ppb was effective up to 3 months, with an IE of 89-95%. Authorities should critically review a reduction of the presently recommended field dosage of 200 ppm novaluron by × 100 or more. This would provide the same efficacy but mitigate environmental pollution, development of vector resistance, and financial losses.
We investigated the physicochemical properties and the biotic interactions of breeding sites of tropical mosquito species. Field sampling was done in 12 study areas in Sri Lanka covering areas with ...secondary natural forests and human settlements. A total of 226 breeding sites were investigated to determine the biotic interactions and physiochemical properties of breeding water (pH, Conductivity, Dissolved Oxygen, Total Dissolved Solids and Temperature). A total of 80.5% of breeding sites from both habitats were positive for mosquito larvae of seven genera and 24 species. Orthopodomyia flavithorax (297) and Aedes albopictus (295) were dominated in tree holes of Alstonia macrophylla, Vateria copallifera and Artocarpus nobilis. Diversity indices showed that the diversity of mosquitoes is high in wet zone habitats of Sri Lanka compared to dry and intermediate zone habitats. Aedes albopictus coexisted with 11 different mosquito species while it avoided larvae of Culex fuscanus, Cx. uniformis and Tripteroides affinis. Strong positive associations were reported between Ae. albopictus and Ar. subalbatus while larvae of Or. flavithorax mosquitoes were not co‐occurred with the larvae of Ae. vittatus, Ae. aegypti, Cx. sitiens, Ar. subalbatus, Anopheles spp and Tr. affinis. The findings identified the breeding adaptability and tolerance to a wide range of physiochemical properties of tropical mosquito communities.
Tropical mosquitoes tolerate a wider range of physiochemical properties (Temperature from 19.8 to 36.8°C, pH between 4.2 and 8.4).
Tree holes of Alstonia macrophylla, Vateria copallifera and Artocarpus nobilis are preferred by Orthopodomyia flavithorax and Aedes albopictus.
Aedes albopictus mostly coexists with larvae of Armigeres subalbatus and avoids the larvae of Culex fuscanus, Cx uniformis and Tripteroides affinis.
The tropical bed bug, Cimex hemipterus, is a serious indoor public health pest in tropical regions causing intense physical discomfort and mental distress to humans. At present, the application of ...insecticides is the major control strategy. The present study was designed to evaluate the development of resistance and resistance mechanisms in Cimex hemipterus from Kandy district, Sri Lanka.
The resistance status of the collected bed bugs was determined against the discriminative dosages of DDT, malathion, propoxur, deltamethrin and permethrin by conducting bioassays according to World Health Organization guidelines. Activities of insecticide metabolizing enzymes, i.e. esterases, glutathione S-transferases (GST) and monooxygenases, and the insensitivity of organophosphate/carbamate target site acetylcholinesterase (AChE), were evaluated by biochemical assays. Regions of the gene of the pyrethroid/DDT target site, the voltage-gated sodium channel regulatory protein (VGSC), were sequenced for possible kdr mutations.
Survival percentages of bed bug population were 71, 68 and 51% for DDT, malathion and propoxur respectively. KT
and KT
values, calculated using log-probit mortality curves for deltamethrin were 62.55 and 123.96 h, respectively. These values were much higher for permethrin where KT
was 201.10 h and the KT
was beyond the detectable range. Results were compared with previous values reported for the same population in 2002. Resistance to propoxur has increased significantly from 11 to 51% with about a 20-fold increase in the number of individuals with elevated esterase mechanism. No significant change has occurred in malathion and DDT resistance, in GST and monooxygenase activities, and in AChE sensitivity for the past 14 years. Six kdr associated mutations (Y/L995H, V1010L, I1011F, L1014F, V1016E, L1017F/S) and a non-kdr associated mutation (A1007S mutation) were found from the α-region of the VGSC gene. Out of the kdr type mutations, only L1014F has been reported previously form C. hemipterus while the others have been reported from other insects.
The bed bug population has developed high resistance to propoxur with increased esterase activities. KT
for deltamethrin and permethrin has increased 125- and 20-fold, respectively, over the period 2002 to 2016. To the authors' knowledge, this is the first time that the possible involvement of a kdr type mutation in developing pyrethroid resistance in C. hemipterus has been shown in Sri Lanka.
Dengue is an important vector-borne disease transmitted by the mosquitoes Aedes aegypti and Ae. albopictus. In the absence of an effective vaccine, vector control has become the key intervention tool ...in controlling the disease. Vector densities are significantly affected by the changing weather patterns of a region. The present study was conducted in three selected localities, i.e., urban Bandaranayakapura, semiurban Galgamuwa, and rural Buluwala in the Kurunegala district of Sri Lanka to assess spatial and temporal distribution of dengue vector mosquitoes and to predict vector prevalence with respect to changing weather parameters. Monthly ovitrap surveys and larval surveys were conducted from January to December 2019 and continued further in the urban area up to December 2021. Aedes aegypti was found moderately in the urban area and to a lesser extent in semiurban but not in the rural area. Aedes albopictus had the preference for rural over urban areas. Aedes aegypti preferred indoor breeding, while Ae. albopictus preferred both indoor and outdoor. For Ae. albopictus, ovitrap index (OVI), premise index (PI), container index (CI), and Breteau index (BI) correlated with both the rainfall (RF) and relative humidity (RH) of the urban site. Correlations were stronger between OVI and RH and also between BI and RF. Linear regression analysis was fitted, and a prediction model was developed using BI and RF with no lag period (R2 (sq) = 86.3%; F = 53.12; R2 (pred) = 63.12%; model: Log10 (BI) = 0.153 + 0.286∗ Log10 (RF); RMSE = 1.49). Another prediction model was developed using OVI and RH with one month lag period (R2 (sq) = 70.21%; F = 57.23; model: OVI predicted = 15.1 + 0.528∗ Lag 1 month RH; RMSE = 2.01). These two models can be used to monitor the population dynamics of Ae. albopictus in urban settings to predict possible dengue outbreaks.
Aedes aegypti and Ae. albopictus are important vectors of human diseases such as dengue, chikungunya, and zika. In Sri Lanka, they have been responsible for transmitting dengue virus. One of the most ...important parameters influencing the likelihood of arbovirus transmission is the age structure of the mosquito population. However, mosquito age is difficult to measure with accuracy. This study aims to construct multivariate calibration models using the transcriptional abundance of three age-responsive genes: Ae15848 (calcium-binding protein), Ae8505 (structural component of cuticle), and Ae4274 (fizzy cell cycle/cell division cycle 20).
The transcriptional age-grading technique was applied to determine the chronological age of Ae. aegypti and Ae. albopictus female mosquito populations from Sri Lanka using the age-responsive genes Ae15848, Ae8505, and Ae4274. Furthermore, Ae. aegypti samples obtained from colonies reared at two temperatures (23 and 27 °C) were used to investigate the influence of temperature on this age-grading technique. Expression levels of these three genes were quantified using reverse transcription qualitative PCR (qRT-PCR), and results were normalized against the housekeeping gene ribosomal gene S17 (RpS17).
The expression of Ae15848 and Ae8505 decreased with the age of mosquitoes and showed the most significant and consistent change while expression of Ae4274 increased with age. The multivariate calibration models showed > 80% correlation between expression of these age-responsive genes and the age of female mosquitoes at both temperatures. At 27 °C the accuracy of age predictions using the models was 2.19 (± 1.66) days and 2.58 (± 2.06) days for Ae. aegypti and Ae. albopictus females, respectively. The accuracy of the model for Ae. aegypti at 23 °C was 3.42 (± 2.74) days.
An adult rearing temperature difference of 4 °C (23-27 °C) did not significantly affect the age predictions. The calibration models created during this study could be successfully used to estimate the age of wild Ae. aegypti and Ae. albopictus mosquitoes from Sri Lanka.
1. Resource partitioning is a critical component in competing species that coexist in a community. The biting behaviour of coexisting frog‐biting mosquito species associated with a tropical anuran ...community is investigated.
2. Monthly samplings were taken for 2 years at two study sites in central Sri Lanka to collect frog‐biting mosquitoes, anuran abundance, environmental data, and interactions between mosquitoes and anuran hosts. Mosquitoes were collected using mouth‐operated aspirators and sound traps broadcasting anuran calls. Mosquitoes were identified using taxonomic keys and DNA barcodes.
3. A total of 1079 frog‐biting mosquitoes from four species belonging to two genera were collected Uranotaenia rutherfordi (5%), Ur. morphotype 1 (67%), Ur. morphotype 2 (21%), and Mansonia uniformis (7%). Species‐specific interactions between Uranotaenia mosquitoes and their anuran host were found. Uranotaenia morphotype 1, the most common species, was mainly attracted (99%) to Duttaphrynus melanostictus. Uranotaenia rutherfordi was mainly attracted (95%) to Pseudophilautus rus, while Ur. morphotype 2 was attracted (97%) to Polypedates cruciger. These Uranotaenia species are active at different hours at night that correspond to the peak calling activity of their anuran host. Each Uranotaenia species was active at heights that coincide with the calling sites of their host. In contrast, Ma. uniformis was non‐specific in host choice and was equally distributed in space and time with respect to host feeding.
4. Here, previously unknown feeding patterns of co‐occurring frog‐biting mosquito species and their interactions with anurans present in their community are reported, highlighting the existence of complex behavioural patterns of these mosquito communities.
Four frog‐biting mosquito species are abundant (Uranotaenia rutherfordi, Ur. morphotype 1, Ur. morphotype 2, and Mansonia uniformis) and commonly attack frogs in Kandy District, Sri Lanka.
These Sri Lankan mosquitoes show phonotaxis behaviour, demonstrating the use of anuran mating calls to locate their
host.
High species specificity of Uranotaenia mosquitoes results in high temporal and spatial niche partitioning among these species.
Avian blood parasites have been shown to have significant health effects on avifauna worldwide. Sri Lanka, a tropical island rich with resident and migratory birds, has not been properly evaluated ...for avian blood parasites or their vectors. We investigated the presence of avian haemoparasites in Sri Lankan birds and the potential mosquito vectors of those pathogens. Blood samples were collected from local/migratory birds captured by standard mist nets from Anawilundawa bird sanctuary, Hanthana mountain range, and the University of Peradeniya park. Mosquitoes were collected from Halgolla forest reserve and the forest patches in Kurunegala and Gampola areas in addition to the above mist-netting localities. Part of the mitochondrial cytochrome b (
cytb
) gene was amplified and sequenced to detect the presence of haemoparasites from avian blood samples (86) and mosquito samples (480). Blood parasites of the two genera, i.e.,
Haemoproteus
(4 species;
Haemoproteus
sp. 1-4) and
Plasmodium
(5 species;
Plasmodium
sp. 1-5) were identified from seven bird species (four resident and three migratory). Among these, three bird species (Red-vented bulbul (3/16), Asian Brown flycatcher (1/1), and India pitta (1/1)) were positive for
Plasmodium
spp., while four (Yellow-browed bulbul (1/4), oriental white-eye (1/4), brown-headed Barbet (1/4), and Indian blue robin (1/1)) were positive for
Haemoproteus
spp. Two mosquito species were also positive for
Plasmodium
(3) and
Haemoproteus
(1) species. Phylogenetic analysis and haplotype networks created using positive sequences of haemoparasites showed that a
Plasmodium
clade was shared by
Cx nigropunctatus
mosquitoes and the migratory bird, Indian pitta. The majority (85%) of the
Plasmodium
and
Haemoproteus
sequences of this study were not linked to the well-characterized species suggesting the distinct nature of the lineages. Associations between mosquito species and blood parasites of birds suggest the possible vector status of these mosquitoes.
Elimination of vector mosquito larvae and their breeding environments is an effective strategy in dengue disease control. Present study examined larval density and water quality in breeding habitats ...and container preference of dengue vectors Ae. aegypti and Ae. albopictus. Larval surveys were conducted monthly in urban, semiurban, and rural sites in Kurunegala, Sri Lanka, from January 2019 to December 2021. Larval densities were recorded under the following three categories: type of container (16 types), type of material (6 types), and location (indoor/outdoor). Breeding preference ratios (BPRs) were calculated using Index of Available Containers and the Index of Contribution to Breeding Sites. Out of 19,234 wet containers examined, larval stages were found in 1,043 habitats. Ae. albopictus larvae were in all three areas whereas Ae. aegypti larvae were restricted to urban areas. Highest number of wet containers and highest positivity were reported from urban followed by semiurban. In general, discarded nondegradable items were the most frequent and mostly positive breeding sites. For Ae. aegypti, the most preferred breeding sites were gutters and concrete slabs. Ae. albopictus mostly preferred concrete slabs in urban areas and tyres in semiurban and rural areas. Material types such as rubber and concrete were mostly preferred by Ae. aegypti whereas ceramic was preferred by Ae. albopictus. Although plastic was the most available material type in all study sites, preference to plastic was low except for urban Ae. albopictus. Both species preferred urban indoor breeding habitats although outdoor breeding was preferred by Ae. albopictus in rural areas. Larval densities of Ae. aegypti and semiurban Ae. albopictus significantly correlated with the BPR of the container type and material type. Dengue vector larvae were found in a 6.7–9.4 pH range. Total dissolved solids and alkalinity positively correlated with preference. Information generated can be successfully used in waste management and public education for effective vector control.
Wolbachia are a group of maternally inherited intracellular bacteria known to be widespread among arthropods. Infections with Wolbachia cause declines of host populations, and also induce host ...resistance to a wide range of pathogens. Over the past few decades, researchers were curious to use Wolbachia as a biological tool to control mosquito vectors. During the present study, assessment of the prevalence of Wolbachia infections among wild mosquito populations in Sri Lanka where mosquito-borne diseases are a major health concern, was carried out for the first time. DNA was extracted from the abdomens of mosquitoes, collected from seven provinces, and screened for the presence of Wolbachia by PCR using wsp and groE primers. Group-specific and strain-specific primers were used to classify Wolbachia into the supergroups A and B, and into the strains Mel, AlbA and Pip.
A total of 330 individual mosquitoes belonging to 22 species and 7 genera were screened. Eighty-seven mosquitoes (26.36%) belonging to four species (i.e. Aedes albopictus, Culex quinquefasciatus, Armigeres subalbatus and Mansonia uniformis) were positive for Wolbachia infections. Primary vector of the dengue fever, Ae. aegypti was negative for Wolbachia infections while the secondary vector, Ae. albopictus, showed a very high infection rate. The filarial vector C. quinquefasciatus had a relatively high rate of infection. Japanese encephalitis vectors C. gelidus and C. triteaneorynchus, and the Anopheles vectors of malaria were negative for Wolbachia infections. Nine sequences of Wolbachia-positive PCR products were deposited in the GenBank and compared with other available data. Aedes albopictus was infected with both Wolbachia strains A (AlbA) and B (Pip) supergroups. Phylogenetic analysis of the wsp sequences showed two major branches confirming identities obtained from the PCR screening with strain-specific primers.
Wolbachia infections were found only among four mosquito species in Sri Lanka: Aedes albopictus, Culex quinquefasciatus, Armigeres subalbatus and Mansonia uniformis. Sequence data showed high haplotype diversity among the Wolbachia strains.
Most mosquito and midge species use hearing during acoustic mating behaviors. For frog-biting species, however, hearing plays an important role beyond mating as females rely on anuran calls to obtain ...blood meals. Despite the extensive work examining hearing in mosquito species that use sound in mating contexts, our understanding of how mosquitoes hear frog calls is limited. Here, we directly investigated the mechanisms underlying detection of frog calls by a mosquito species specialized on eavesdropping on anuran mating signals: Uranotaenia lowii. Behavioral, biomechanical and neurophysiological analyses revealed that the antenna of this frog-biting species can detect frog calls by relying on neural and mechanical responses comparable to those of non-frog-biting species. Our findings show that in Ur. lowii, contrary to most species, males do not use sound for mating, but females use hearing to locate their anuran host. We also show that the response of the antennae of this frog-biting species resembles that of the antenna of species that use hearing for mating. Finally, we discuss our data considering how mosquitoes may have evolved the ability to tap into the communication system of frogs.
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