Mosquito Oviposition Research Articles

Pesticide‐mediated trophic cascade and an ecological trap for mosquitoes

AbstractBroad‐spectrum pesticides can have immediate toxic effects both on target pest species and on non‐target species. They may also have positive residual effects on mosquitoes after pesticide degradation, by altering the community structure, that is, by reducing abundances of mosquito competitors and predators, and via a trophic cascade, which may increase food resources for mosquito larvae. Alternatively, if a pesticide‐mediated trophic cascade results in toxic or inedible algae, the pesticide can act as an ecological trap for some taxa by attracting oviposition in sites where algae are abundant but unsuitable. The present study assessed mosquito oviposition habitat selection, mosquito larval performance, and community structure alterations after applications of various pesticides. The experiment was conducted in outdoor mesocosms assigned to one of four treatments: (1) control, no pesticides; (2) Bacillus thuringiensis var. israelensis (Bti), a narrow‐spectrum bacterium well known for its larvicidal activity on mosquitoes and other dipterans; (3) temephos, an organophosphate mosquito larvicide with community‐wide spectrum effects; and (4) pyriproxyfen, a pyridine‐based insect growth regulator (IGR) class with wide‐spectrum effects. Soon after pesticide application, Culex pipiens oviposition was highest in the control pools. Invertebrate species richness and abundance were strongly reduced in the broad‐spectrum pesticide treatments (temephos and pyriproxyfen) when compared to control. One month after pesticide application, Cx. pipiens oviposition was highest in the pyriproxyfen‐treated pools, although larval survival remained lowest in the pyriproxyfen‐treated pools. Our results suggest that pyriproxyfen causes a chemically mediated trophic cascade and provides an ecological trap, that is, attracting mosquito oviposition due to an altered community structure, but causing high mosquito larval mortality.

The effect of pond dyes on oviposition and survival in wild UK Culex mosquitoes.

British Culex pipiens complex [Culex pipiens sensu lato) mosquito distribution, abundance, and potential for disease transmission are intimately linked to their environment. Pond and lake dyes that block light to restrict algal photosynthesis are a relatively new product assumed to be an environmentally friendly since they are based on food dyes. Their use in urban garden ponds raises questions linked to mosquito oviposition, since coloured water can be an attractant. Culex (mostly pipiens) is commonly found in UK gardens and is a potential vector of viruses including the West Nile Virus (WNV). Any factors that significantly change the distribution and population of Cx pipiens could impact future risks of disease transmission. A gravid trap was used to catch female Cx pipiens mosquitoes for use in oviposition choice tests in laboratory and semi-field conditions. Two types of pond dye, blue and shadow (which looks slightly red), were tested for their impact on oviposition and survival of wild caught Cx pipiens. There were no significant differences in the number of egg batches laid when gravid mosquitoes were given a choice between either blue dye and clear water or shadow dye and clear water indicating that these dyes are not attractants. Larvae hatched from egg batches laid by wild-caught gravid females were used to measure survival to adulthood with or without dye, in a habitat controlled to prevent further colonisation. The experiment was run twice, once in the summer and again in the autumn, whereas the dyes had no impact on emergence in the summer, there were highly significant reductions in emergence of adults in both dye treated habitats in the autumn. Containers with or without shadow dye were placed outside to colonise naturally and were sampled weekly for larvae and pupae over a 6 month period through summer and autumn. There was a significant negative effect of shadow dye on pupal abundance in a three week period over the summer, but otherwise there was no effect. It is likely that population abundance and food was a more powerful factor for mosquito survival than the dye.

Impacts of Meteorological Parameters on the Abundance of Malaria Vector in Batticaloa District, Sri Lanka

Malaria is one of the most widespread Vector-BorneDiseases (VBDs) in the world causing serious losses to the health and economy. Out of many factors, meteorological parameters effects on malaria distribution significantly. Conditions including higher temperature, lower relative humidity and higher wind velocity are found to be affecting on mosquito oviposition, propagation and survival. In Sri Lanka, Batticaloawas considered as one of the malaria endemicdistrictsduring recentpast. Control and effective management in these areas had been difficult due to the lack of reliable data, human resource and the deterioration of the infrastructure caused by years of armed conflict. This study was carried out to identify the relationships exist between different malaria vectors and meteorological parameters in the district of Batticaloa.Entomological surveillance was carried out in three potential malaria sensitive areas (Vakarai, Vakaneri and Mandur) with a radius of 20km in the district of Batticaloa from April 2013 to July 2014. Adult mosquito samples were collected monthly by WHO standard method; Cattle Baited Net Collection (CBNT). Monthly meteorological parameters (T: mean temperature, RF: total rainfall, WS: wind speed and RH: Relative humidity) during the study period were also collected from the Department of Meteorology. Data were analyzed using SPSS version 15.0. Pearson’s correlation coefficients (r) at 0.05 probability were used to investigate the relationships among meteorological variables of the current month along with lag time period of two months and vector densities. The most dominant mosquito species in the area was An. subpictuswith a relative abundance of 31.56% while An. nigerrimuswas the second highest (21.22%). Significant relationships were only observed with RH and WS where, An. nigerrimus showed a negative moderate relationship (r=0.372; p=0.03) while An. subpictus showed a positive relationship (r= 0.375; p=0.029) with RH. In addition, An. subpictusalsoshowed a negative relationship with one month lagged time of WS. The findings of the study reveal that the relationships that exist between the vector and the meteorological parameters are complicated and unpredictable. Neither patterns nor consistencies were observed in these relationships. The adaptation of vector and the influence of other environmental and anthropological factors on the vector mosquito could be the reason for this behaviour. Keywords:Malaria, Vector, Abundance, Relative humidity, Wind speed

Exploiting oviposition pheromone-an innovative way to control mosquitoes

Mosquitoes have tremendous impact on both human and animal health as vectors of serious diseases. The mosquito oviposition pheromone (MOP, caproic acid), can be employed in an ‘attract and kill’ strategy as an alternative approach in control of mosquitoes. MOP (1 ppm) was impregnated in both vapour patch and Whatmann no.1 filter paper as well as encapsulated in calcium alginate beads for sustained release. The impregnated vapour patch as well as filter paper were air dried and placed in plastic cups containing 250 ml of water and left undisturbed indoors for a period of 24 hours. Similarly, plain vapour patch and plain filter paper without pheromone impregnation were kept as control. The number of mosquito egg rafts in cups containing pheromone lure as well as control was monitored and counted. The egg rafts were removed and destroyed by drying in the sun. An ovi-trap was designed and field trials were carried out to assess its efficacy. In-vitro trials for a period of one month revealed 89.28%, 3.57%, 7.14% of Culex spp. egg rafts deposited by adult mosquitoes in containers with pheromone impregnated vapour patches, filter paper and calcium alginate encapsulated with 1 ppm concentration of MOP, respectively whereas, no Culex egg raft was observed in the controls. These ovi-traps can be effectively used for the control of mosquitoes.

Regional Survey of Mosquito Control Knowledge and Usage In North Carolina.

Mosquitoes are a nuisance and can transmit pathogens to humans and other animals, resulting in notable morbidity and mortality. Organized mosquito control programs conduct surveillance, source reduction, treatment of mosquito oviposition sites, and adulticiding to protect public health. However, in some regions, there has been a decline in county and municipal mosquito control programs, and homeowners increasingly contract with private mosquito control companies or address mosquito-related issues themselves at the household level. The extent to which these services are being used, the potential for mosquito and/or insecticide exposure around the home, and the access to these services by individuals of different socioeconomic categories are not known. We conducted regional (western, central, eastern) assessments of public perception and knowledge of mosquito control services in a variety of communities of different socioeconomic categories (low, moderate, high) and types (urban, suburban, rural) in 3 North Carolina counties. We also assessed the respondents' basic knowledge of mosquito-borne diseases. Most respondents thought mosquito control was important to protect against both nuisance mosquitoes and mosquito-borne disease. The majority of people would pay ≤$50/year for mosquito control and most thought this should be covered by municipal/county taxes. Many respondents (31%, 95% confidence interval [CI] 26-35%) personally undertake mosquito control on their properties, but only 5.3% (95% CI 3.1-7.5%) contract with professional mosquito control services, with no significant differences between region, community type, or socioeconomic category in the proportion using private mosquito control services. While there were significant differences between factor levels (3 regions, 3 community types, 3 socioeconomic categories) in some responses, there were no significant differences observed between respondents, regardless of factor level, in the willingness to contribute funds to a community-based mosquito control program.

Complex Effects of Superior Competitors and Resources on Culex restuans (Diptera: Culicidae) Oviposition.

A growing body of literature on mosquito oviposition behavior supports the hypothesis that females place eggs in habitats that provide best available opportunity for growth, development, and maturation of their offspring. We conducted a field experiment to evaluate Culex oviposition behavior in response to the interspecific competitor Aedes triseriatus (Say) (Diptera: Culicidae) larvae, and resources in the form of quantity of plant detritus, and dissolved nitrogen (TN) and phosphorus (TP) derived from that detritus. We tested a set of specific predictions: 1) As a poorer competitor, Culex will avoid ovipositing in containers with superior interspecific competitors; 2) Culex choose oviposition habitats that contain greater amount of resources for the microbial food of their offspring; 3) Sufficiently high resource abundance can override avoidance of oviposition in containers with interspecific competitors. Culex restuans Theobald (Diptera: Culicidae) was the only species ovipositing, and the oviposition responses changed over time. The effect of resources was more important in driving oviposition decisions at the beginning and end of the experiment. The amount of resources, as manifest by TN and TP concentrations, had differential effects on oviposition. At the beginning females laid more eggs in containers with low detritus, which had the highest TN. After that, females preferred those containers with high detritus, which had low TN and high TP. The effect of competitors was important only during the middle of the experiment. Paradoxically, even as a poorer competitor Cx. restuans preferentially oviposited in containers with late-instar Ae. triseriatus, suggesting that the presence of successful heterospecifics indicates a good quality larval habitat.

Effects of flash flooding on mosquito and community dynamics in experimental pools.

Pulsed disturbances of larval mosquito sites are likely to have a direct negative effect on mosquitoes but may also have indirect effects due to the alteration of community structure. These altered communities may become attractive to gravid mosquitoes searching for oviposition sites when the disturbances decrease the abundance of mosquito antagonists such as competitors, which often results in an increase in mosquito food resources. However, flash flood disturbances in intermittent riverbeds can also remove mosquito food resources such as algae, so that the net effect of flash floods could be either to increase or decrease mosquito abundance. We conducted an outdoor mesocosm experiment to assess the effects of flash floods on mosquito oviposition habitat selection and larval abundance during the post-disturbance period of community recovery. Mesocosms were artificially flooded. Mosquito oviposition, immature abundance, invertebrate species diversity, chlorophyll a, and abiotic parameters were monitored. Our results showed that the flash flood negatively affected phytoplankton and zooplankton, leading to a decrease of mosquito oviposition in flooded mesocosms compared to non-flooded mesocosms. More broadly, this study indicates how disturbances influence mosquito oviposition habitat selection due to the loss of food resources in ephemeral pools, and it highlights the importance of considering the effects of disturbances in management, habitat restoration, and biodiversity conservation in temporary aquatic habitats.

Modelling the impact of the long-term use of insecticide-treated bed nets on Anopheles mosquito biting time

BackgroundEvidence of changing in biting and resting behaviour of the main malaria vectors has been mounting up in recent years as a result of selective pressure by the widespread and long-term use of insecticide-treated bed nets (ITNs), and indoor residual spraying. The impact of resistance behaviour on malaria intervention efficacy has important implications for the epidemiology and malaria control programmes. In this context, a theoretical framework is presented to understand the mechanisms determining the evolution of feeding behaviour under the pressure of use of ITNs.MethodsAn agent-based stochastic model simulates the impact of insecticide-treated bed nets on mosquito fitness by reducing the biting rates, as well as increasing mortality rates. The model also incorporates a heritability function that provides the necessary genetic plasticity upon which natural selection would act to maximize the fitness under the pressure of the control strategy.ResultsThe asymptotic equilibrium distribution of mosquito population versus biting time is shown for several daily uses of ITNs, and the expected disruptive selection on this mosquito trait is observed in the simulations. The relative fitness of strains that bite at much earlier time with respect to the wild strains, when a threshold of about 50% of ITNs coverage highlights the hypothesis of a behaviour selection. A sensitivity analysis has shown that the top three parameters that play a dominant role on the mosquito fitness are the proportion of individuals using bed nets and its effectiveness, the impact of bed nets on mosquito oviposition, and the mosquito genetic plasticity related to changing in biting time.ConclusionBy taking the evolutionary aspect into account, the model was able to show that the long-term use of ITNs, although representing an undisputed success in reducing malaria incidence and mortality in many affected areas, is not free of undesirable side effects. From the evolutionary point of view of the parasite virulence, it should be expected that plasmodium parasites would be under pressure to reduce their virulence. This speculative hypothesis can eventually be demonstrated in the medium to long-term use of ITNs.

Mosquito female response to the presence of larvivorous fish does not match threat to larvae

1. Several species with complex life‐history traits such as amphibians and insects with aquatic immature stages and terrestrial adults avoid ovipositing in pools containing larvivorous fish. This avoidance response was assumed to be a general one for most fish species.2. The generality of ovipositing Culex to the presence of three, widespread larvivorous fish species was tested in a set of field experiments with artificial oviposition pools using caged fish.3. Larval performance was further examined under actual predation by these three fish species.4. Results show that ovipositing females responded strongly to the presence of caged mosquitofish, Gambusia affinis, while showing no significant response to the presence of caged green sunfish, Lepomis cyanellus, or the pirate perch, Aphredoderus sayanus. All three fish species consumed similar amounts of larvae.5. This is the first example of species‐specific response differences to predators during mosquito oviposition habitat selection. These results point to the existence of predator‐released kairomones affecting mosquito behaviour. These kairomones may either be species‐specific or vary in concentration among fish, and probably have an important role in the understanding of mosquito spatial distribution.

Mosquito distribution in a saltmarsh: determinants of eggs in a variable environment

Two saltmarsh mosquitoes dominate the transmission of Ross River virus (RRV, Togoviridae: Alphavirus), one of Australia's most prominent mosquito-borne diseases. Ecologically, saltmarshes vary in their structure, including habitat types, hydrological regimes, and diversity of aquatic fauna, all of which drive mosquito oviposition behavior. Understanding the distribution of vector mosquitoes within saltmarshes can inform early warning systems, surveillance, and management of vector populations. The aim of this study was to identify the distribution of Ae. camptorhynchus, a known vector for RRV, across a saltmarsh and investigate the influence that other invertebrate assemblage might have on Ae. camptorhynchus egg dispersal. We demonstrate that vegetation is a strong indicator for Ae. camptorhynchus egg distribution, and this was not correlated with elevation or other invertebrates located at this saltmarsh. Also, habitats within this marsh are less frequently inundated, resulting in dryer conditions. We conclude that this information can be applied in vector surveillance and monitoring of temperate saltmarsh environments and also provides a baseline for future investigations into understanding mosquito vector habitat requirements.

Zingiber cernuum (Zingiberaceae) essential oil as effective larvicide and oviposition deterrent on six mosquito vectors, with little non-target toxicity on four aquatic mosquito predators.

Mosquitoes are responsible for the transmission of many pathogens and parasites, which cause serious diseases in humans and animals. Currently, botanical products have been suggested as alternative tools in the fight against arthropod vectors. In this study, the essential oil (EO) extracted from Zingiber cernuum was tested as larvicide and oviposition deterrent on six mosquito species of public health relevance, including malaria and Zika virus vectors. The EO showed high toxicity on third instar larvae of Anopheles stephensi (LC50=41.34μg/ml), Aedes aegypti (LC50=44.88μg/ml), Culex quinquefasciatus (LC50=48.44μg/ml), Anopheles subpictus (LC50=51.42μg/ml), Aedes albopictus (LC50=55.84μg/ml), and Culex tritaeniorhynchus (LC50=60.20μg/ml). In addition, low doses of Z. cernuum EO reduced oviposition rates in six mosquito species. The acute toxicity of Z. cernuum EO on four mosquito predators was scarce; LC50 ranged from 3119 to 11,233μg/ml. Overall, our results revealed that the Z. cernuum EO can be considered for the development of effective and environmental-friendly mosquito larvicides and oviposition deterrents.

Testing the link between perceived and actual risk of predation: mosquito oviposition site selection and egg predation by native and introduced fish

SummaryAccording to the threat‐sensitivity hypothesis, prey avoidance behaviour should reflect the magnitude of predation risk. Since predation can strongly affect reproduction success, ovipositing females are expected to adaptively adjust their predator avoidance response, or local breeding patch selectivity, in accordance with the perceived level of threat posed for their progeny by specific predators. However, association between avoidance and predation can be disrupted when the prey and the predator lack spatiotemporal opportunities to co‐evolve, such as in cases of non‐native predator introductions.We examined the interactions between mosquitoes (from the genusCulex) and three species of sympatric predaceous freshwater fish, a native cyprinidBarbus paludinosus, a cichlidPseudocrenilabrus philanderand an introduced poeciliid, the western mosquitofishGambusia affinis.In an outdoor mesocosm experiment, we quantified patterns ofCulexoviposition site selection across fish species using free‐roaming, caged and fish‐free treatments. In a complementary laboratory experiment, we tested the effectiveness of each fish species as predators of mosquito eggs and larvae.Synthesis and applications. We found evidence for: (i) mosquito egg raft predation by free‐roaming fish; (ii) fish‐specific avoidance by ovipositingCulex; and (iii) a positive association between fish‐specific oviposition avoidance and fish‐specific efficiency as an egg predator. These results contribute towards a better understanding of predator–prey co‐evolution, predator‐borne cue recognition, and suggest local native fish, the southern mouthbrooderPseudocrenilabrus philander, as an alternative toGambusiafor the biocontrol ofCulexmosquitoes.

Cedrol, a malaria mosquito oviposition attractant is produced by fungi isolated from rhizomes of the grass Cyperus rotundus.

BackgroundCedrol, a sesquiterpene alcohol, is the first identified oviposition attractant for African malaria vectors. Finding the natural source of this compound might help to elucidate why Anopheles gambiae and Anopheles arabiensis prefer to lay eggs in habitats containing it. Previous studies suggest that cedrol may be a fungal metabolite and the essential oil of grass rhizomes have been described to contain a high amount of different sesquiterpenes.ResultsRhizomes of the grass Cyperus rotundus were collected in a natural malaria mosquito breeding site. Two fungi were isolated from an aqueous infusion with these rhizomes. They were identified as Fusarium falciforme and a species in the Fusarium fujikuroi species complex. Volatile compounds were collected from the headspace above fungal cultures on Tenax traps which were analysed by gas chromatography–mass spectrometry (GCMS). Cedrol and a cedrol isomer were detected in the headspace above the F. fujikuroi culture, while only cedrol was detected above the F. falciforme culture.ConclusionCedrol an oviposition attractant for African malaria vectors is produced by two fungi species isolated from grass rhizomes collected from a natural mosquito breeding site.

Fern-synthesized silver nanocrystals: Towards a new class of mosquito oviposition deterrents?

Mosquitoes act as vectors of devastating pathogens and parasites, representing a key threat for millions of humans and animals worldwide. Eco-friendly control tools are urgently required. We proposed a novel method of fern-mediated biosynthesis of silver nanoparticles (AgNP) using Dicranopteris linearis, acting as a reducing and capping agent. AgNP were characterized by UV–vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), zeta potential and particle size analysis. In mosquitocidal assays, the LC50 of D. linearis extract against Aedes aegypti ranged from 165.213 (larva I) to 255.055ppm (pupa). LC50 of D. linearis-synthesized AgNP ranged from 18.905 (larva I) to 29.328ppm (pupa). In the field, the application of D. linearis extract and AgNP (10×LC50) led to 100% larval reduction after 72h. Smoke toxicity experiments conducted against A. aegypti adults showed that D. linearis leaf-, stem- and root-based coils evoked mortality rates comparable to the permethrin-based positive control (58%, 47%, 34%, and 48% respectively). In ovicidal experiments, egg hatchability was reduced by 100% after treatment with 25ppm of AgNP and 300ppm of D. linearis extract. Interestingly, oviposition deterrent assays highlighted that 100ppm of fern extract reduced oviposition rates of more than 65%, while 10ppm of fern-fabricated AgNP reduced oviposition rates of more than 70% in A. aegypti (OAI were −0.52 and −0.55, respectively). Overall, our results highlighted that D. linearis-synthesized AgNP could be useful candidates to develop nano-formulated oviposition deterrents effective against dengue vectors.

'Nature or nurture': survival rate, oviposition interval, and possible gonotrophic discordance among South East Asian anophelines.

BackgroundMosquito survival, oviposition interval and gonotrophic concordance are important determinants of vectorial capacity. These may vary between species or within a single species depending on the environment. They may be estimated by examination of the ovaries of host-seeking mosquitoes.MethodsLanding collections, Furvela tent-trap and CDC light-trap collections were undertaken sequentially in four locations in Cambodia between February 2012 and December 2013 and samples from the collected mosquitoes were dissected to determine parity, sac stage (indicative of time spent prior to returning to feed) and egg stage.ResultsA total of 27,876 Anopheles from 15 species or species groups were collected in the four locations and 2883 specimens were dissected. Both the density and predominant species collected varied according to location and trapping method. Five species were dissected in sufficient numbers to allow comparisons between locations. Estimated oviposition interval differed markedly between species but less within species among different locations. Anopheles aconitus had the shortest cycle, which was 3.17 days (95 % CI 3–3.64), and Anopheles barbirostris had the longest cycle, which took four days (95 % CI 3.29–4). Anopheles minimus had a higher sac rate in weeks leading up to a full moon but there was apparently little effect of moon phase on Anopheles dirus. Despite the fact that many of the species occurred at very low densities, there was no evidence of gonotrophic dissociation in any of them, even during sustained hot, dry periods. The principal Cambodian malaria vector, An. dirus, was only common in one location where it was collected in miniature light-traps inside houses. It did not appear to have an exceptional survival rate (as judged by the low average parous rate) or oviposition cycle.ConclusionsDifferences in the oviposition interval were more pronounced among species within locations than within species among ecologically diverse locations. A nationwide survey using CDC light-traps for the collection of An. dirus inside houses may help in determining patterns of malaria transmission in Cambodia.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1389-0) contains supplementary material, which is available to authorized users.

The distribution and occurrence of mosquito larvae (Diptera: Culicidae) in the Tongatapu Island Group, Kingdom of Tonga

The global expansion of air, sea and land transport networks has greatly enhanced the spread of mosquitoes internationally. In the Pacific, the incidence of mosquito-borne diseases has been increasing in recent years. The Kingdom of Tonga has had numerous disease outbreaks from dengue fever and chikungunya viruses over recent years. Previous research has catalogued mosquito species occurrences and distributions throughout Tonga. However, it is unknown whether new species have arrived in Tonga, and if distribution of previously found species has changed since the last comprehensive survey in 2006. Consequently, we conducted a mosquito larval survey between November and December 2013 at 84 sites across four islands (Tongatapu, Pangaimotu, 'Oneata and 'Eua) in the Tongatapu Island Group to record the distribution and occurrence of mosquito larvae. Larvae were more frequently collected in artificial (e.g. abandoned car tyres, 55-gallon plastic drums and plastic containers) than natural (e.g. pools, ponds and tree holes) habitats. Larvae of nine mosquito species were collected in the Tongatapu Island Group: Aedes aegypti, A. albopictus, A. tongae, A. horrescens, A. vexans nocturnus, Culex annulirostris, C. albinervis, C. quinquefasciatus and C. sitiens. Eight species were collected on Tongatapu Island (A. horrescens being absent), four species on 'Oneata Island (A. albopictus, A. horrescens, C. quinquefasciatus and C. annulirostris), four species on 'Eua Island (A. aegypti, A. albopictus, A. tongae and C. quinquefasciatus) and one on Pangaimotu Island (A. aegypti). Species collected from 'Eua and 'Oneata islands represent first-time collections of these species on these islands. Aedes aegypti, A.albopictus and C. quinquefasciatus were the three most common species collected and have markedly increased their distribution since the 2006 survey. The collection of A. albopictus is the second time that this species has been recorded in Tonga; however, the spatial extent of this species throughout Tongatapu was far greater than previously recorded. Management should focus on reducing the number of artificial habitats by covering, emptying or infilling these habitats with soil to minimise mosquito oviposition. This should reduce the abundance of mosquitoes and help prevent disease outbreak in Tonga.

Oviposition of Culex tarsalis (Diptera: Culicidae) Differs on Water Conditioned by Potential Fish and Insect Predators.

The response of egg-laying Culex tarsalis Coquillett (Diptera: Culicidae) to water conditioned by three fish species used for mosquito control and three predatory aquatic insect species was examined in laboratory binary choice experiments. Oviposition by Cx. tarsalis was 72% less on water conditioned with the arroyo chub, Gila orcutti (Eigenmann & Eigenmann) (Cypriniformes: Cyprinidae) relative to control cups containing aged tap water, but no significant difference was found in the numbers of egg rafts laid on water conditioned with the fathead minnow (Pimephales promelas (Rafinesque), Cypriniformes: Cyprinidae) and the control treatment (water aged 24 h). Mosquito oviposition on water conditioned with the predominantly herbivorous/algivorous California Mozambique tilapia hybrid (Oreochromis mossambicus (Peters) × Oreochromis urolepis hornorum L. (Perciformes: Cichlidae)) or predatory insects (nymphs: Sympetrum corruptum (Hagen) (Odonata: Libellulidae); adults: Thermonectus basillaris (Harris) or Cybister fimbriolatus (Say) (Coleoptera: Dytiscidae)) did not differ significantly relative to that onto water aged for 24 h. As compared with water aged 24 h and water conditioned with diving beetles, oviposition by Cx. tarsalis was significantly lower (≥53%) when live predatory diving beetles were present in oviposition cups. Gravid Cx. tarsalis females do not respond equally to putative semiochemicals in water conditioned with the piscine or aquatic insect predators of immature mosquitoes tested here.

Bioinsecticide and leaf litter combination increases oviposition and reduces adult recruitment to create an effective ovitrap for Culex mosquitoes.

Mosquito egg traps, aquatic habitats baited with oviposition attractant and insecticide, are important tools for surveillance and control efforts in integrated vector management programs. The bioinsecticide Bacillus thuringiensis subsp. israelensis (Bti) is increasingly used as an environmentally friendly alternative to chemical insecticides and the combination of Bti with a simple oviposition attractant like leaf litter to create an effective egg trap seems appealing. However, previous research suggests that Bti may itself alter oviposition, and that leaf litter may dramatically reduce Bti toxicity. Here we present results from field experiment designed to link the effects of litter and Bti on mosquito oviposition habitat selection and post-colonization survival to production of adult mosquitoes. Tripling litter increased Culex spp. oviposition nearly nine-fold, while Bti had no effect on oviposition. Neither factor altered egg survival, thus larval abundance reflected the effects of litter on oviposition. Both Bti and litter reduced larval survival by ∼60%. We found no evidence that increased litter reduced Bti toxicity. Adult production was dependent upon both litter and Bti. In the absence of Bti, effects of litter on oviposition translated into three-fold more adults. However, in the presence of Bti, initial increases in oviposition were erased by the combined negative effects of Bti and litter on post-colonization survival. Thus, our study provides field evidence that combined litter and Bti application creates an effective ovitrap. This combined treatment had the highest oviposition and the lowest survival, and thus removed the greatest number of mosquitoes from the landscape.

Ovicidal, oviposition deterrent and larvicidal response of Anopheles stephensi Liston, 1901 to Lobophora variegata Lamouroux, 1817 from Tuticorin coast, Gulf of Mannar, India

The objective of the present study was to investigate the mosquito ovicidal, oviposition deterrent and larvicidal efficacy of hexane, benzene, chloroform, ethyl acetate and methanol extracts of, Lobophora variegata against malarial vector Anopheles stephensi. Among the five extract tested, the methanol extract was notable, which attained the 100 percent mortality at the concentration of 200.0 ppm and the hatchability rate ranged from 71.3 to 36.3 percent. In laboratory oviposition deterrent test, the extract of L. variegata greatly reduced the number of eggs deposited by gravid An. stephensi. The maximum and significant diminished fecundity in An. stephensi was observed with methanol extract which caused 76.15­–97.69% effective deterrence. Larvicidal response of An. stephensi was more susceptible in methanol extract. The LC50 ­value of methanol extract was 61.63 ppm and the Chi-square value were significant at p<0.05 level. It is concluded, that the extract of L. variegata could be used in control of malarial vector An. stephensi.

Ovicidal, oviposition deterrent and larvicidal response of Anopheles stephensi Liston, 1901 to Lobophora variegata Lamouroux, 1817 from Tuticorin coast, Gulf of Mannar, India

The objective of the present study was to investigate the mosquito ovicidal, oviposition deterrent and larvicidal efficacy of hexane, benzene, chloroform, ethyl acetate and methanol extracts of, Lobophora variegata against malarial vector Anopheles stephensi . Among the five extract tested, the methanol extract was notable, which attained the 100 percent mortality at the concentration of 200.0 ppm and the hatchability rate ranged from 71.3 to 36.3 percent. In laboratory oviposition deterrent test, the extract of L. variegata greatly reduced the number of eggs deposited by gravid An. stephensi . The maximum and significant diminished fecundity in An. stephensi was observed with methanol extract which caused 76.15­–97.69% effective deterrence. Larvicidal response of An. stephensi was more susceptible in methanol extract. The LC 50 ­value of methanol extract was 61.63 ppm and the Chi-square value were significant at p <0.05 level. It is concluded, that the extract of L. variegata could be used in control of malarial vector An. stephensi .