Hatching response of Aedes aegypti (Diptera: Culicidae) eggs at low temperatures: effects of hatching media and storage conditions

Temporal dynamics of the egg bank of Aedes aegypti (Diptera: Culicidae) in the winter-spring transition in a temperate region

In temperate regions, the populations of Aedes aegypti (L.) (Diptera: Culicidae) remain in the egg stage during the winter. In Buenos Aires, Argentina, a temperate region in the southern limit of Ae. aegypti distribution, the start of the next reproductive season and the rate of increase of the adult population depend on the egg bank that remains after the winter. This study aimed to analyze the mortality, field-hatching, and survival of eggs exposed to field conditions representative of those that occur in nature. In addition, the post-exposure hatching response of the eggs was assessed. Four egg batches were exposed to natural conditions starting in mid-winter and were recovered progressively after 3, 6, 9, and 12 weeks. One egg batch (initial control) was not exposed in the field and remained under laboratory conditions. After the exposure period, the recovered intact, collapsed, and hatched eggs were counted. Intact eggs were immersed three times in the laboratory to study their hatching response. Progressive increases in the proportion of lost (presumably by predation), dead, and hatched eggs in successive egg batches were recorded. Field-hatching was recorded from late winter onwards. The first hatchings occurred in conditions probably not favorable to complete development into reproductive adults. A progressive decrease in live eggs was observed, with 51% of the recovered eggs alive after 12 weeks of exposure. In the laboratory, the hatching response in the first immersion was low for the initial control and for the eggs exposed for 3 weeks, and increased for successive cohorts. The results confirm that the survival of Ae. aegypti eggs in the winter-spring transition ensures persistence throughout the next favorable season in Buenos Aires City. The observed inhibition to hatch of the first batches might relate to a photoperiod-induced diapause, as observed in previous studies.

Enhancing the scalability of Wolbachia-based vector-borne disease management: time and temperature limits for storage and transport of Wolbachia-infected Aedes aegypti eggs for field releases

BACKGROUND

Introgression of the bacterial endosymbiont Wolbachia into Aedes aegypti populations is a biocontrol approach being used to reduce arbovirus transmission. This requires mass release of Wolbachia-infected mosquitoes. While releases have been conducted using a variety of techniques, egg releases, using water-soluble capsules containing mosquito eggs and larval food, offer an attractive method due to its potential to reduce onsite resource requirements. However, optimisation of this approach is required to ensure there is no detrimental impact on mosquito fitness and to promote successful Wolbachia introgression.

METHODS

We determined the impact of storage time and temperature on wild-type (WT) and Wolbachia-infected (wMel or wAlbB strains) Ae. aegypti eggs. Eggs were stored inside capsules over 8 weeks at 18 °C or 22 °C and hatch rate, emergence rate and Wolbachia density were determined. We next examined egg quality and Wolbachia density after exposing eggs to 4-40 °C to determine how eggs may be impacted if exposed to extreme temperatures during shipment.

RESULTS

Encapsulating eggs for 8 weeks did not negatively impact egg viability or resulting adult emergence and Wolbachia density compared to controls. When eggs were exposed to temperatures within 4-36 °C for 48 h, their viability and resulting adult Wolbachia density were maintained; however, both were significantly reduced when exposed to 40 °C.

CONCLUSIONS

We describe the time and temperature limits for maintaining viability of Wolbachia-infected Ae. aegypti eggs when encapsulated or exposed to extreme temperatures. These findings could improve the efficiency of mass releases by providing transport and storage constraints to ensure only high-quality material is utilised during field releases.

A systematic review and meta-analysis of the effects of temperature on the development and survival of the Aedes mosquito

Introduction

The Aedes mosquito species, which are the vectors for the transmission of the dengue virus (DENV) to humans, are becoming increasingly susceptible to the formidable effects of influential factors, especially temperature. However, there are still very few studies that have systematically reviewed the existing literature. Hence, in the present study, a systematic literature review and meta-analysis was conducted into the effects of temperature on dengue vectors.

Method

Several research methodologies were incorporated into the current study, and a review was carried out using PRISMA as a guide. The publications for this study were chosen from two prominent databases, Scopus and Web of Science. All of the studies were assessed, reviewed, and evaluated independently by two reviewers. The meta-analysis tool, Review Manager (RevMan Copenhagen Version 5.4.1), was used to record the extracted data for the meta-analysis. Moran's I ² and a funnel plot were utilized to measure heterogeneity, and publication bias was investigated. A 95% confidence interval (CI) and overall risk difference (RD) were estimated using a random-effects model.

Result and discussion

As a consequence of the search efforts, a total of 46 articles were selected for inclusion in the systematic review and meta-analysis. This review was divided into five major themes, based on a thematic analysis: (i) hatching rate, (ii) development time, (iii) longevity, (iv) survival rate, and (v) wing morphology. In addition, the development time, survival rate, and wing morphology revealed significantly higher risk differences between the maximum and minimum temperatures (RD: 0.26, 95% CI: 0.16, 0.36; p = < 0.00001; RD: 0.10, 95% CI: 0.05, 0.14; p < 0.0001; and RD: 0.07, 95% CI: 0.02, 0.12; p = 0.006, respectively). This study makes several substantial contributions to the body of knowledge and to practical applications. Finally, a number of recommendations are made at the conclusion of this research for the future reference of researchers.

Photoperiod affects female life history traits in temperate populations of Aedes aegypti from South America

In many insects, short photoperiods induce females to lay diapausing eggs, which are associated with a reduction in female fecundity, and/or with an increase in their growth rate, allowing for a larger size at adulthood. The effects of short photoperiods may also differ among populations, depending on the different selection pressures imposed by the winter conditions. Thus, this study aimed to experimentally assess the effects of short photoperiods on Aedes aegypti, an invasive mosquito species that also vectors several viral diseases. We compared life history parameters of the females reared from the first larval instar under contrasting photoperiods, in two populations from the temperate region of Argentina, one with a milder winter (BA) and the other with a harsher winter (SB). The results showed a significant increase in the time to oviposition, a trend to a larger size of females (significant only for SB) and higher inhibition of egg hatching (more pronounced in SB), in response to short photoperiods. No differences in fecundity were detected among treatments. The different reaction norms of the populations in female body size and egg hatching response suggest an adaptation to local conditions, which might favour a further expansion of A. aegypti towards colder climates.

Winter survival of Aedes aegypti (Diptera: Culicidae) eggs at its southern limit distribution

Aedes aegypti (L.) (Diptera: Culicidae) survives in the egg stage under unfavorable environmental conditions. In this study, we assessed the survival of Ae. aegypti eggs under natural winter conditions as an overwintering mechanism. To address this, field collected eggs (from Buenos Aires city) were exposed for three months during the winter season in three sites of Santa Rosa and General Acha (La Pampa province, Argentina). Eggs survival and hatching response were analyzed considering two factors (site of exposure and time of oviposition). Of the 1397 analyzed eggs, 936 (67%) were viable at the end of the study. Egg survival showed to be high in all sites (between 53% and 84%), except in one site of Santa Rosa. Also, eggs survival was higher in eggs laid in May (94%) (late-fall) as compared to those laid in March (61%) and April (56%) (early- and mid-fall respectively). Eggs hatching response was only affected by the time of oviposition, being lower for eggs laid in May (33%) as compared to March (38%) and April (50%). These results provide information regarding the winter resistance of Ae. aegypti at the limit of its distribution in temperate regions. Given the high percentages of survival found in this study, we consider that the low winter temperatures would not be a limitation for its establishment in southern areas.

Oviposition dynamics of Aedes aegypti in Central Argentina

Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae) is the vector of multiple arboviruses. To evaluate the association between environmental factors and the oviposition activity of Ae. aegypti in Argentina, data on the presence and abundance of eggs were collected using ovitraps, between September of 2018 and May of 2019, in the cities of Villa María, Río Cuarto and Salsipuedes (Córdoba province, Argentina). We analysed the relationships between oviposition and five environmental factors: Temperature, precipitation, vegetation cover, human population density and distance to sites with a potential high density of larval habitats, like cemeteries and trash dumps. Environmental factors' data were collected using satellite image products. The oviposition activity was randomly distributed in three cities. Using generalized linear mixed models, we show that the house where each ovitrap was placed was a source of variability in oviposition, suggesting the relevance of microsite factors and the importance of domestic control actions. Ae. aegypti oviposition was positively correlated with night-time temperature of the previous 3 weeks, and in a context-dependent manner, it was positively correlated with human population density, vegetation cover and precipitation. The consistency and magnitude of these relationships varied between cities, indicating that oviposition is related to a complex system of environmental variables.

Effect of Parental Photoperiod on Body Size and Developmental Time of Aedes aegypti (Diptera: Culicidae) in Buenos Aires City

Many insects use photoperiod as a signal to anticipate upcoming unfavorable conditions. Photoperiod sensitivity may be a relevant factor in Aedes (Stegomyia) aegypti (L.) populations at the cool margins of the species' range, where winter conditions have a strong effect on population dynamics. In this study, we evaluated the effect of parental photoperiod on preimaginal survival and developmental time, and on wing length for the first generation of Ae. aegypti from a temperate region (Buenos Aires City, Argentina). Our experiment started with eggs from parents exposed to short-day (SD; 10:14 [L:D]) or long-day (LD; 14:10 [L:D]) photoperiods during their entire life span. Eggs were stored under the same photoperiod (SD or LD) as their parents for 91 d, until immersion. After hatching, larvae were reared until adult emergence in thermal baths at one of two constant temperatures (17 or 23°C), at a photoperiod of 12:12 (L:D) h and fed ad libitum. Survival from larva I to adult emergence was not affected either by parental photoperiod or rearing temperature. At a rearing temperature of 23°C, female offspring from the SD parental photoperiod developed faster and had shorter wings compared with those from the LD parental photoperiod. No effect of parental photoperiod was observed on female offspring reared at 17°C. In male offspring, parental photoperiod had no effect on developmental time and wing length, independently of the rearing temperature. Results indicate that the parental photoperiod may affect some offspring traits. This effect may be a characteristic of Ae. aegypti populations in temperate regions to deal with the winter conditions.

The ecophysiological plasticity of Aedes aegypti and Aedes albopictus concerning overwintering in cooler ecoregions is driven by local climate and acclimation capacity

Aedes aegypti and Aedes albopictus transmit diseases such as dengue, and are of major public health concern. Driven by climate change and global trade/travel both species have recently spread to new tropic/subtropic regions and Ae. albopictus also to temperate ecoregions. The capacity of both species to adapt to new environments depends on their ecophysiological plasticity, which is the width of functional niches where a species can survive. Mechanistic distribution models often neglect to incorporate ecophysiological plasticity especially in regards to overwintering capacity in cooler habitats. To portray the ecophysiological plasticity concerning overwintering capability, we conducted temperature experiments with multiple populations of both species originating from an altitudinal gradient in South Asia and tested as follows: the cold tolerance of eggs (-2 °C- 8 days and - 6 °C- 2 days) without and with an experimental winter onset (acclimation: 10 °C- 60 days), differences between a South Asian and a European Ae. albopictus population and the temperature response in life cycles (13 °C, 18 °C, 23 °C, 28 °C). Ecophysiological plasticity in overwintering capacity in Ae. aegypti is high in populations originating from low altitude and in Ae. albopictus populations from high altitude. Overall, ecophysiological plasticity is higher in Ae. albopictus compared to Ae. aegypti. In both species acclimation and in Ae. albopictus temperate continental origin had a huge positive effect on survival. Our results indicate that future mechanistic prediction models can include data on winter survivorship of both, tropic and subtropic Ae. aegypti, whereas for Ae. albopictus this depends on the respective temperate, tropical region the model is focusing on. Future research should address cold tolerance in multiple populations worldwide to evaluate the full potential of the ecophysiological plasticity in the two species. Furthermore, we found that Ae. aegypti can survive winter cold especially when acclimated and will probably further spread to colder ecoregions driven by climate change.

A dynamic, ensemble learning approach to forecast dengue fever epidemic years in Brazil using weather and population susceptibility cycles

Transmission of dengue fever depends on a complex interplay of human, climate and mosquito dynamics, which often change in time and space. It is well known that its disease dynamics are highly influenced by multiple factors including population susceptibility to infection as well as by microclimates: small-area climatic conditions which create environments favourable for the breeding and survival of mosquitoes. Here, we present a novel machine learning dengue forecasting approach, which, dynamically in time and space, identifies local patterns in weather and population susceptibility to make epidemic predictions at the city level in Brazil, months ahead of the occurrence of disease outbreaks. Weather-based predictions are improved when information on population susceptibility is incorporated, indicating that immunity is an important predictor neglected by most dengue forecast models. Given the generalizability of our methodology to any location or input data, it may prove valuable for public health decision-making aimed at mitigating the effects of seasonal dengue outbreaks in locations globally.

Differential inhibition of egg hatching in Aedes aegypti populations from localities with different winter conditions

In Argentina, the mosquito Aedes aegypti (L.) (Diptera: Culicidae) is distributed from subtropical to temperate climates. Here, we hypothesized that the expansion of Ae. aegypti into colder regions is favoured by high-phenotypic plasticity and an adaptive inhibition of egg hatching at low temperatures. Thus, we investigated the hatching response of eggs of three populations: one from a subtropical region (Resistencia) and two from temperate regions (Buenos Aires City and San Bernardo) of Argentina. Eggs collected in the field were raised in three experimental colonies. F1 eggs were acclimated for 7 days prior to immersion at 7.6 or 22°C (control eggs). Five immersion temperatures were tested: 7.6, 10.3, 11.8, 14.1 and 16°C (range of mean winter temperatures of the three localities). A second immersion at 22°C was performed 2 weeks later to assess the inhibition to hatch under favourable conditions. After the first immersion, we compared the proportions of hatched eggs and dead larvae among treatment levels, whereas after the second immersion we compared the hatching response among the three populations. The factors that most influenced the egg hatching response were the geographical origin of the populations and the immersion temperature, but not the acclimation temperature. The proportions of hatching and larval mortality at low temperatures were higher for Resistencia than for Buenos Aires and San Bernardo, whereas the hatching response at ambient temperature was lower for San Bernardo than for Buenos Aires and Resistencia. The results support the hypothesis that populations from colder regions show an adaptive inhibition of egg hatching.

Analysis and forecast of dengue incidence in urban Colombo, Sri Lanka

BACKGROUND

Understanding the dynamical behavior of dengue transmission is essential in designing control strategies. Mathematical models have become an important tool in describing the dynamics of a vector borne disease. Classical compartmental models are well-known method used to identify the dynamical behavior of spread of a vector borne disease. Due to use of fixed model parameters, the results of classical compartmental models do not match realistic nature. The aim of this study is to introduce time in varying model parameters, modify the classical compartmental model by improving its predictability power.

RESULTS

In this study, per-capita vector density has been chosen as the time in varying model parameter. The dengue incidences, rainfall and temperature data in urban Colombo are analyzed using Fourier mathematical analysis tool. Further, periodic pattern of the reported dengue incidences and meteorological data and correlation of dengue incidences with meteorological data are identified to determine climate data-driven per-capita vector density parameter function. By considering that the vector dynamics occurs in faster time scale compares to host dynamics, a two dimensional data-driven compartmental model is derived with aid of classical compartmental models. Moreover, a function for per-capita vector density is introduced to capture the seasonal pattern of the disease according to the effect of climate factors in urban Colombo.

CONCLUSIONS

The two dimensional data-driven compartmental model can be used to predict weekly dengue incidences upto 4 weeks. Accuracy of the model is evaluated using relative error function and the model can be used to predict more than 75% accurate data.

Diapause influenced oviposition behavior and physical egg hatch cues of Aedes atropalpus (Diptera: Culicidae): traits that may influence successful colonization of riverine rock pools

Mosquitoes have developed specialized oviposition strategies that allow them to develop in a wide variety of aquatic habitats. Environmentally cued hatching traits may also play an important role in the successful colonization of some larval habitats, but this subject has remained largely unexplored in Culicidae. Aedes atropalpus (Coquillett) is an autogenous rock pool specialist that may maintain unique adaptations for oviposition and egg hatching. We investigated the egg-laying strategies of Ae. atropalpus exposed to standard (non-diapausing) rearing conditions and diapause-inducing conditions and tested the impact of physical agitation on egg hatch rates by exposing floating and submerged eggs to physical agitation treatments. The results of the oviposition experiment indicate that Ae. atropalpus females primarily lay non-diapausing eggs directly onto the water surface and lay diapausing eggs directly on solid surfaces. The egg-hatching experiment demonstrated that physical agitation significantly increases Ae. atropalpus hatch rates. Floating and submerged eggs responded similarly to the agitation treatment. These data suggest that oviposition behaviors based on both egg diapause status and environmentally-cued hatching strategies may be important adaptations for Ae. atropalpus in riverine rock pools.

Linking Mosquito Ecology, Traits, Behavior, and Disease Transmission

Mosquitoes are considered to be the deadliest animals on Earth because the diseases they transmit claim at least a million human lives every year globally. Here, we discuss the scales at which the effects of ecological factors cascade to influence epidemiologically relevant behaviors of adult mosquitoes. In particular, we focused our review on the environmental conditions (coarse-scale variables) that shape the life-history traits of larvae and adult mosquitoes (fine-scale traits), and how these factors and their association, in turn, modulate adult behaviors to influence mosquito-borne disease transmission. Finally, we explore the integration of physical, physiological, and behavioral information into predictive models with epidemiological applications.

Effects of Constant and Fluctuating Low Temperatures on the Development of Aedes aegypti (Diptera: Culicidae) from a Temperate Region

Most studies of the effects of low temperature on the development of immature stages of Aedes aegypti (L.) have been performed at constant temperatures in the laboratory, which may not accurately reflect the variable environmental conditions in the field. Thus, the aim of this study was to assess the effect of constant temperatures (CT) and fluctuating low temperatures (FT) on the fitness of Ae. aegypti of Buenos Aires, Argentina. Three CT treatments (12, 14, and 16°C) and three FT treatments (12, 14, and 16°C ± 4°C) were performed and then survival, development time, and size of adults analyzed for each treatment. The immature stages completed development in all the treatments, with an average survival of 88% at 16°C, 85% at 14°C, and 22% at 12°C, and showed no differences between the CT and FT treatments. Development times were similar between the CT and FT treatments at 16°C (average ± SD: 22.7 ± 2.0 d) and at 14°C (average ± SD: 30.5 ± 2.5 d), whereas at 12°C, they lasted longer under CT (average ± SD: 46.6 ± 5.1 d) than under FT (average ± SD: 37 ± 6.5 d). The sizes of the adults at 12 and 14°C were similar but larger than those at 16°C, and showed no differences between the CT and FT treatments. Compared to populations of other geographical regions assessed in previous studies, the shorter development times and the high survival at 14 and 16°C, and the ability to complete development at 12°C, a fact not previously reported, suggest that the Ae. aegypti population of Buenos Aires city has a higher tolerance to these conditions.

Temperature impacts on dengue emergence in the United States: Investigating the role of seasonality and climate change

Tropical mosquito-borne viruses have been expanding into more temperate regions in recent decades. This is partly due to the coupled effects of temperature on mosquito life history traits and viral infection dynamics and warming surface temperatures, resulting in more suitable conditions for vectors and virus transmission. In this study, we use a deterministic ordinary differential equations model to investigate how seasonal and diurnal temperature fluctuations affect the potential for dengue transmission in six U.S. cities. We specifically consider temperature-dependent mosquito larval development, adult mosquito mortality, and the extrinsic incubation period of the virus. We show that the ability of introductions to lead to outbreaks depends upon the relationship between a city's temperature profile and the time of year at which the initial case is introduced. We also investigate how the potential for outbreaks changes with predicted future increases in mean temperatures due to climate change. We find that climate change will likely lead to increases in suitability for dengue transmission and will increase the periods of the year in which introductions may lead to outbreaks, particularly in cities that typically have mild winters and warm summers, such as New Orleans, Louisiana, and El Paso, Texas. We discuss our results in the context of temperature heterogeneity within and across cities and how these differences may impact the potential for dengue emergence given present day and predicted future temperatures.

Effects of multiple transmission pathways on Zika dynamics

Although the Zika virus is transmitted to humans primarily through the bite of infected female Aedes aegypti mosquitoes, it can also be sexually and vertically transmitted within both populations. In this study, we develop a new mathematical model of the Zika virus which incorporates sexual transmission in humans and mosquitos, vertical transmission in mosquitos, and mosquito to human transmission through bites. Analysis of this deterministic model shows that the secondary transmission routes of Zika increase the basic reproductive number (R0) of the virus by 5%, shift the peak time of an outbreak to occur 10% sooner, increase the initial growth of an epidemic, and have important consequences for control strategies and estimates of R0. Furthermore, sensitivity analysis show that the basic reproductive number is most sensitive to the mosquito biting rate and transmission probability parameters and reveal that the dynamics of juvenile mosquito stages greatly impact the peak time of an outbreak. These discoveries deepen our understanding of the complex transmission routes of ZIKV and the consequences that they may hold for public health officials.

Competition among Aedes aegypti larvae

Adult Aedes aegypti mosquitoes are important vectors of human disease. The size of the adult female affects her success, fitness, and ability to transmit diseases. The size of the adults is determined during the aquatic larval stage. Competition among larvae for food influences the size of the pupa and thus the adult. In these experiments, the food level (mg/larva) and the density (larvae/vial) both affect intraspecific competition, which shows up as the interaction of the two factors. Furthermore, the total food per vial affects the nature of competition among the larvae, also apparent in the interaction of food and density. Male larvae are affected by the percent of males in the vial, but females are not. Seven biologically significant dependent variables were examined, and the data analyzed by multivariate analysis of variance to gain insight into the relationships among the variables and the effects of these factors on the larvae as they grew in small containers. Male and female larvae compete differently from one another for the particulate yeast cells in this experiment; female larvae outcompete males through larger size and by retaining cells within their gut at low total food levels. Under conditions of more intense competition, the pupal masses of both males and females are smaller, so the effect of competition is a reduced apparent food level. The age at pupation is also affected by food and density. Across the twenty treatment combinations of food/larva and larvae/vial, female larvae grew as though there were six different ecological environments while male larvae grew as though there were only four different environments. No interference competition was observed. Eradication efforts aimed at adult populations of this mosquito may inadvertently increase the size and robustness of the next generation of larvae, resulting in a subsequent adult population increase in the second generation.

First report of Stegomyia aegypti (= Aedes aegypti) in Mexico City, Mexico

Stegomyia aegypti (= Aedes aegypti) (Diptera: Culicidae) is a species of mosquito that is currently widespread in Mexico. Historically, the mosquito has been distributed across most tropical and subtropical areas lower than 1700 m a.s.l. Currently, populations that are found at higher altitudes in regions with cold and dry climates suggest that these conditions do not limit the colonization and population growth of S. aegypti. During a survey of mosquitoes in September 2015, larvae of S. aegypti mosquitoes were found in two different localities in Mexico City, which is located at about 2250 m a.s.l. Mexico City is the most populous city in Mexico and has inefficient drainage and water supply systems. These factors may result in the provision of numerous larval breeding sites. Mosquito monitoring and surveillance are now priorities for the city.

Egg Hatching and Survival of Immature Stages of Aedes aegypti (Diptera: Culicidae) Under Natural Temperature Conditions During the Cold Season in Buenos Aires, Argentina

In temperate regions, the seasonal dynamics of Aedes aegypti (L.) (Diptera: Culicidae) is mainly influenced by temperature. It is assumed that, during the winter season, the population remains as eggs and that the development and population growth of surviving eggs begin during the following spring. The aim of the current study was to assess egg hatching of Ae. aegypti during the winter in Buenos Aires city (Argentina), and analyze the survival of immature stages. The experiments consisted of immersing eggs and studying the development of immature stages of cohorts from June and September under natural temperature conditions. The proportion of hatched eggs was compared between weeks of immersion and related to environmental variables. Survival was compared among cohorts and the development rate was related to the mean temperature during development. The results showed that, with few exceptions, egg hatching was over 45% during the winter period. The proportion of hatched eggs was positively associated with immersion temperature, pre-immersion temperature and photoperiod. The immature stages completed the development during the cold season, with a trend toward increased survival of late-hatching cohorts. Survival was 30% at 13.2 °C and above 90% at 20 °C, whereas the development time at low temperatures was 49.4 d at 13.2 °C and 17.7 d at 20 °C. The high hatching and survival compared with other studies suggest that the local population might be adapting to winter conditions. The anticipated emergence of adults would be adaptive if they are able to reproduce successfully in the early spring.

Coffee and its waste repel gravid Aedes albopictus females and inhibit the development of their embryos

BACKGROUND

Dengue is a prevalent arboviral disease and the development of insecticide resistance among its vectors impedes endeavors to control it. Coffee is drunk by millions of people daily worldwide, which is associated with the discarding of large amounts of waste. Coffee and its waste contain large amounts of chemicals many of which are highly toxic and none of which have a history of resistance in mosquitoes. Once in solution, coffee is brownish in colour, resembling leaf infusion, which is highly attractive to gravid mosquitoes. To anticipate the environmental issues related to the increasing popularity of coffee as a drink, and also to combat insecticide resistance, we explored the deterrence potentials of coffee leachates against the ovipositing and embryonic stages of the dengue vector, Aedes albopictus.

METHODS

In a series of choice, no-choice, and embryo toxicity bioassays, we examined changes in the ovipositional behaviours and larval eclosion of Ae. albopictus in response to coffee extracts at different concentrations.

RESULTS

Oviposition responses were extremely low when ovicups holding highly concentrated extract (HCE) of coffee were the only oviposition sites. Gravid females retained increased numbers of mature eggs until 5 days post-blood feeding. When provided an opportunity to oviposit in cups containing coffee extracts and with water, egg deposition occurred at lower rates in those containing coffee, and HCE cups were far less attractive to females than those containing water only. Females that successfully developed in a coffee environment preferentially oviposited in such cups when in competition with preferred oviposition sites (water cups), but this trait did not continue into the fourth generation. Larval eclosion occurred at lower rates among eggs that matured in a coffee environment, especially among those that were maintained on HCE-moistened substrates.

CONCLUSIONS

The observations of the present study indicate a pronounced vulnerability of Ae. albopictus to the presence of coffee in its habitats during the early phases of its life cycle. The observations that coffee repels gravid females and inhibits larval eclosion provide novel possibilities in the search for novel oviposition deterrents and anti-larval eclosion agents against dengue vectors.