Biological control of Culicidae with the copepod Mesocyclops aspericornis and larvivorous fish (Poeciliidae) in a village of French Polynesia

The copepod Mesocyclops aspericornis Daday and the larvivorous fishes Gambusia affinis (B. & G.) and Poecilia reticulata R. & B., were released into mosquito breeding sites in Tuherahera village, Tikehau atoll, French Polynesia, to control larvae of Aedes aegypti (L.), Ae.polynesiensis Marks, Culex annulirostris Skuse and Cx quinquefasciatus Say. Treatments were completed within a week, in January 1990. Fish quickly eliminated mosquito larvae from the open breeding sites (ponds, wells). The impact of copepods in water tanks, drums and covered wells was inconsistent, apparently depending on the availability of microfaunal diet for growth of copepod nauplii. As the biting rate of adult Ae.aegypti seemed to be unaffected by the biological control of larvae, this village-scale experiment was judged to be unsuccessful as a means of vector control.     

Occurrence of Toxorhynchites guadeloupensis (Dyar Knab) in oviposition trap of Aedes aegypti (L.) (Diptera: Culicidae)

Toxorhynchites guadeloupensis (Dyar Knab), a poorly known mosquito species, was observed preying upon Aedes aegypti (L.) larvae, in an oviposition trap placed for routine dengue entomological surveillance, during 2003-2004 in the urban area of Boa Vista, Roraima, Brazil. This is the first report for Tx. guadeloupensis using Ae. aegypti oviposition traps as breeding places. This finding may have important consequences in the epidemiology and local dengue control since Ae. aegypti density is a basic variable in dengue prediction. Whether predation of Ae aegypti by Tx. guadeloupensis in the Amazon is of significance, is a question to be examined. Also, larval predation may be a cause for underestimation of the actual Ae aegypti numbers. Together these hypotheses need to be better investigated as they are directly related to dengue epidemiology, to the success of any outbreak prediction and surveillance program.     

Effects of Toxorhynchites moctezuma larval predation on Aedes aegypti populations: experimental evaluation

Abstract. Predatory larvae of the mosquito Toxorhynchites moctezuma were used experimentally to control a standing crop of larvae of the dengue vector mosquito Ae.aegypti. Each week, fifty Ae.aegypti first instar larvae were introduced to each of five water-filled drums (220 litres) of the type commonly used for domestic water storage in Caribbean dwellings. At the beginning of the fourth week, a certain number (0, 1, 2, 5 or 10) of first instar Tx.moctezuma larvae were introduced to each drum and the daily yield of Ae.aegypti adults from each drum was monitored thereafter. The experiment was repeated three times. With only one or two Tx.moctezuma larvae, predation on Ae.aegypti larvae stopped the output of Ae.aegypti adults for 1 week. Five or ten Tx. moctezuma prevented any Ae.aegypti emergence for up to 16 weeks. Cannibalism among Tx. moctezuma larvae was seldom observed and appeared not to be a hindrance in using this species against Ae.aegypti. Thus Tx.moctezuma is regarded as a good candidate for the biological control of Ae.aegypti by augmentative releases.     

Larval development of Aedes aegypti and Aedes albopictus in peri-urban brackish water and its implications for transmission of arboviral diseases

Aedes aegypti (Linnaeus) and Aedes albopictus Skuse mosquitoes transmit serious human arboviral diseases including yellow fever, dengue and chikungunya in many tropical and sub-tropical countries. Females of the two species have adapted to undergo preimaginal development in natural or artificial collections of freshwater near human habitations and feed on human blood. While there is an effective vaccine against yellow fever, the control of dengue and chikungunya is mainly dependent on reducing freshwater preimaginal development habitats of the two vectors. We show here that Ae. aegypti and Ae. albopictus lay eggs and their larvae survive to emerge as adults in brackish water (water with <0.5 ppt or parts per thousand, 0.5-30 ppt and >30 ppt salt are termed fresh, brackish and saline respectively). Brackish water with salinity of 2 to 15 ppt in discarded plastic and glass containers, abandoned fishing boats and unused wells in coastal peri-urban environment were found to contain Ae. aegypti and Ae. albopictus larvae. Relatively high incidence of dengue in Jaffna city, Sri Lanka was observed in the vicinity of brackish water habitats containing Ae. aegypti larvae. These observations raise the possibility that brackish water-adapted Ae. aegypti and Ae. albopictus may play a hitherto unrecognized role in transmitting dengue, chikungunya and yellow fever in coastal urban areas. National and international health authorities therefore need to take the findings into consideration and extend their vector control efforts, which are presently focused on urban freshwater habitats, to include brackish water larval development habitats.     

Larvicide and oviposition deterrent effects of fruit and leaf extracts from Melia azedarach L. on Aedes aegypti (L.) (Diptera: Culicidae)

Aedes aegypti (L.) (Diptera: Culicidae), the main urban vector of dengue, has developed resistance to various insecticides, making its control increasingly difficult. We explored the effects of Argentine Melia azedarach L. (Meliaceae) fruit and senescent leaf extracts on Ae. aegypti larval development and survival, by rearing cohorts of first instar mosquitoes in water with different extract concentrations. We also analysed oviposition deterrent activity in choice tests with extract-treated ovitraps. The leaf extract showed a strong larvicide activity, with all larvae dying before pupation, and significantly delayed development time. It strongly inhibited oviposition by Ae. aegypti females. The fruit extract showed much weaker effects. This first report of highly effective larvicidal, growth regulating and oviposition deterrent activity of a senescent leaf extract of M. azedarach against Ae. aegypti, suggests that such extract could represent a promising tool in the management of this mosquito pest.     

State‐wide survey of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Florida

Aedes aegypti and Aedes albopictus are invasive mosquito species with geographic ranges that have oscillated within Florida since their presence was first documented. Local transmission of dengue, chikungunya, and Zika viruses serves as evidence of the public health importance of these two species. It is important to have detailed knowledge of their distribution to aid in mosquito control efforts and understand the risk of arbovirus transmission to humans. Through a partnership involving the University of Florida Institute of Food and Agricultural Sciences Cooperative Extension Service and the Florida Medical Entomology Laboratory; the Florida Department of Health; and mosquito control agencies throughout Florida, a container mosquito surveillance program involving all life stages was launched in the summer of 2016 to detect the presence of Ae. aegypti and Ae. albopictus. Results from this survey were mapped to provide a picture of the current known distribution of Ae. aegypti and Ae. albopictus in Florida. Aedes aegypti and/or Ae. albopictus were detected in the 56 counties that were part of the survey. Only Aedes albopictus was detected in 26 counties, primarily in the panhandle region of Florida. The results of this work underscore the importance of maintaining container mosquito surveillance in a state where chikungunya, dengue, and Zika viruses are present and where there is continued risk for exotic arbovirus introductions.     

Laboratory evaluation of Mesocyclops annulatus (Wierzejski, 1892) (Copepoda: Cyclopidea) as a predator of container-breeding mosquitoes in Argentina

In laboratory bioassays we tested the predatory capacity of the copepod Mesocyclops annulatus on Aedes aegypti and Culex pipiens larvae. A single adult female of M. annulatus caused 51.6% and 52.3% mortality of 50 first instar larvae of Ae. aegypti and Cx. pipiens respectively, in a 72 h test period. When alternative food was added to the containers, mortality rates declined to 16% and 10.3% for Ae. aegypti and Cx. pipiens respectively. When 50 first instar larvae of each of the two mosquito species tested were placed together with a single adult female of M. annulatus, mortality rates were 75.5% for Ae. aegypti larvae and 23.5% for Cx. pipiens larvae in a three day test period. Different density of adult females of M. annulatus ranged from 5 to 25 females produced mortality rates of Ae. aegypti first instar larvae from 50% to 100% respectively. When a single adult female of M. annulatus was exposed to an increasing number of first-instar Ae. aegypti larvae ranging from 10 to 100, 100% mortality was recorded from 1 to 25 larvae, then mortality declined to 30% with 100 larvae. The average larvae killed per 24 h period by a single copepod were 29.     

Seasonal distribution and species composition of daytime biting mosquitoes

Adults and immatures of Aedes mosquito populations were collected at temperatures between 40 and 44°C (summer), while larvae were collected at 0°C (winter). Major mosquito activities were observed from February to mid-December at various collection sites that yielded high populations of Aedes spp. from May to September, and high populations of Culex spp. and Anopheles spp. from March to September. In June to July, mosquito activity was suspended because the relative humidity was high (70%); a result of the monsoon rains. In August, with temperature ranging from 38 to 42°C, the populations of Culex , Anopheles and Aedes began to increase (36.8, 32.1 and 26.3%, respectively). Population estimates (through standard prototype Centers for Disease Control (CDC) and Biogents (BG)-sentinel) and species composition of Aedes in forest habitats indicated a rapid increase in the populations of Ae. albopictus (52.3%), Ae. aegypti (19.1%) and Ae. vittatus (28.5%) following the rainy season in July. Areas positive for Ae. albopictus had identical population levels and distribution ranges of Ae. vittatus , however, there were no Ae. aegypti in Ae. albopictus areas from August to September. The population level, seasonal distribution, habitat and areas of adult activity marked by global positioning system (GPS) coordinates are being used for reference and for species composition data of Anopheles spp. (2), Culex spp. (10) and Aedes spp. (5) in addition to associated temperature, relative humidity and physico-chemical factors of larval habitat. Global meteorological changes have caused an expansion of the active period, leading to the mosquito's possibility of being a vector of disease increasing, resulting in the spread of dengue fever.     

Population dynamics of Aedes aegypti and dengue as influenced by weather and human behavior in San Juan, Puerto Rico

Previous studies on the influence of weather on Aedes aegypti dynamics in Puerto Rico suggested that rainfall was a significant driver of immature mosquito populations and dengue incidence, but mostly in the drier areas of the island. We conducted a longitudinal study of Ae. aegypti in two neighborhoods of the metropolitan area of San Juan city, Puerto Rico where rainfall is more uniformly distributed throughout the year. We assessed the impacts of rainfall, temperature, and human activities on the temporal dynamics of adult Ae. aegypti and oviposition. Changes in adult mosquitoes were monitored with BG-Sentinel traps and oviposition activity with CDC enhanced ovitraps. Pupal surveys were conducted during the drier and wetter parts of the year in both neighborhoods to determine the contribution of humans and rains to mosquito production. Mosquito dynamics in each neighborhood was compared with dengue incidence in their respective municipalities during the study. Our results showed that: 1. Most pupae were produced in containers managed by people, which explains the prevalence of adult mosquitoes at times when rainfall was scant; 2. Water meters were documented for the first time as productive habitats for Ae. aegypti; 3. Even though Puerto Rico has a reliable supply of tap water and an active tire recycling program, water storage containers and discarded tires were important mosquito producers; 4. Peaks in mosquito density preceded maximum dengue incidence; and 5. Ae. aegypti dynamics were driven by weather and human activity and oviposition was significantly correlated with dengue incidence.     

Parasitoid-induced behavioral alterations of Aedes aegypti mosquito larvae infected with mermithid nematodes (Nematoda: Mermithidae).

A wide range of parasites are known to cause behavioral changes in their hosts and parasitized insects are especially amenable to the study of such changes. The majority of studies addressing parasite-induced behavioral alterations have focused on parasites with complex life cycles and the adaptive nature of such changes. Behavioral changes caused by parasitoids, single-host parasites that kill their host upon emergence, have been studied less and the adaptive nature of these changes is likely to be different than those in complex life cycles. I investigated behavioral alterations in Aedes aegypti mosquito larvae infected with parasitoid nematodes (family Mermithidae). I conducted several experiments in which I tested the following hypotheses: 1) Mermithid nematodes induce behavioral changes in mosquito larvae and the changes are density dependent. 2) Different species of mermithid nematodes induce similar changes in mosquito larvae behavior. 3) Behavioral alterations vary with mermithid developmental stage. 4) Mosquito larvae infected with mermithid nematodes behave similarly to uninfected food-deprived mosquito larvae. I found that 4th instar Ae. aegypti infected with Romanomermis culicivorax or Strelkovimermis spiculatus exhibited resting behaviors significantly more often than uninfected controls but that intensity of infection did not affect activity levels. In earlier instars, infected mosquito larvae were more active than uninfected control larvae in some behaviors associated with feeding. There was no significant difference between infected and uninfected food-deprived mosquitoes in nine of the ten behaviors observed. The decrease in activity of late instar Ae. aegypti larvae infected with mermithids may be a parasitoid adaptation that reduces the risk of predation and thus increases host and parasitoid survival. The increase in feeding activity in earlier instars as well as the similarity between uninfected food-deprived and infected Ae. aegypti behavior may indicate that these behaviors are adaptive for the parasitoid, increasing nutritional acquisition for successful parasitoid development.     

The first report of Aedes (Stegomyia) albopictus in Haiti

Aedes albopictus was found in six of the 10 departments of Haiti and in 14 of the 35 communes surveyed. The survey found the larvae of Ae. albopictus in 13 different types of containers. Used tires and tins were by far the most common breeding sites used by this mosquito species. At the breeding sites, Ae. albopictus was associated with other mosquito species, such as Aedes aegypti, Culex nigripalpus and Aedes mediovittatus. The highest proportion of association was with Ae. aegypti. This study represents the first report of Ae. albopictus in Haiti.     

Biochemical and cytoimmunological evidence for the control of Aedes aegypti larval trypsin with Aea-TMOF

Trypsin and chymotrypsin-like enzymes were detected in the gut of Aedes aegypti in the four larval instar and pupal developmental stages. Although overall the amount of trypsin synthesized in the larval gut was 2-fold higher than chymotrypsin, both enzymes are important in food digestion. Feeding Aea-Trypsin Modulating Oostatic Factor (TMOF) to Ae. aegypti and Culex quinquefasciatus larvae inhibited trypsin biosynthesis in the larval gut, stunted larval growth and development, and caused mortality. Aea-TMOF induced mortality in Ae. aegypti, Cx. quinquefasciatus, Culex nigripalpus, Anopheles quadrimaculatus, and Aedes taeniorhynchus larvae, indicating that many mosquito species have a TMOF-like hormone. The differences in potency of TMOF on different mosquito species suggest that analogues in other species are similar but may differ in amino acid sequence or are transported differently through the gut. Feeding of 29 different Aea-TMOF analogues to mosquito larvae indicated that full biological activity of the hormone is achieved with the tetrapeptide YDPA. Using cytoimmunochemical analysis, intrinsic TMOF was localized to ganglia of the central nervous system in larvae and male and female Ae. aegypti adults. The subesophageal, thoracic, and abdominal ganglia of both larval and adult mosquitoes contained immunoreactive cells. Immunoreactive cells were absent in the corpus cardiacum of newly molted 4th instar larvae but were found in late 4th instar larvae. In both males and females, the intrinsic neurosecretory cells of the corpus cardiacum were filled with densely stained immunoreactive material. These results indicate that TMOF-immunoreactive material is synthesized in sugar-fed male and female adults and larvae by the central nervous system cells.     

Dynamics of the "popcorn" Wolbachia infection in outbred Aedes aegypti informs prospects for mosquito vector control

Forty percent of the world's population is at risk of contracting dengue virus, which produces dengue fever with a potentially fatal hemorrhagic form. The wMelPop Wolbachia infection of Drosophila melanogaster reduces life span and interferes with viral transmission when introduced into the mosquito Aedes aegypti, the primary vector of dengue virus. Wolbachia has been proposed as an agent for preventing transmission of dengue virus. Population invasion by Wolbachia depends on levels of cytoplasmic incompatibility, fitness effects, and maternal transmission. Here we characterized these traits in an outbred genetic background of a potential target population of Ae. aegypti using two crossing schemes. Cytoplasmic incompatibility was strong in this background, and the maternal transmission rate of Wolbachia was high. The infection substantially reduced longevity of infected adult females, regardless of whether adults came from larvae cultured under high or low levels of nutrition or density. The infection reduced the viability of diapausing and nondiapausing eggs. Viability was particularly low when eggs were laid by older females and when diapausing eggs had been stored for a few weeks. The infection affected mosquito larval development time and adult body size under different larval nutrition levels and densities. The results were used to assess the potential for wMelPop-CLA to invade natural populations of Ae. aegypti and to develop recommendations for the maintenance of fitness in infected mosquitoes that need to compete against field insects.     

First report of the oriental mosquito Aedes albopictus on the West African island of Bioko,Equatorial Guinea

The invasive oriental mosquito Aedes (Stegomyia) albopictus (Skuse) (Diptera: Culicidae) was detected on Bioko Island for the first time in November 2001. It was found to be well established breeding in artificial containers at Planta, near Malabo, the capital of Equatorial Guinea. Associated species of mosquito larvae were Aedes aegypti (L.), Ae. africanus (Theobald), Culex near decens Theobald, Cx. duttoni Theobald, Cx. quinquefasciatus Say, Cx. tigripes De Grandpré & De Charmoy, Eretmapodites quinquevittatus Theobald and Mansonia africana (Theobald). This is the third tropical African country to be invaded by Ae. albopictus, which has recently spread to many parts of the Americas and Europe--with vector competence for dengue, yellow fever and other arboviruses. In the Afrotropical environment, it will be interesting to monitor the ecological balance and/or displacement between introduced Ae. albopictus and indigenous Ae. aegpyti (domestic, peri-domestic and sylvatic populations).     

Geographic genetic variation in populations of the dengue virus vector Aedes aegypti

Isoenzyme variation was assessed in 79 mosquito samples of Aedes aegypti, and susceptibility to a dengue 2 virus strain was evaluated in 83 samples. Analysis of FST values, differentiation indexes, and geographic distances separating populations revealed that genetic differences between populations depended on the species' history of migration and colonization. Three major clusters were identified: (1). the sylvan form, Ae. ae. formosus, from West Africa and some islands in the Indian Ocean; (2). the domestic form, Ae. ae. aegypti, from Southeast Asia and South America; and (3). Ae. ae. aegypti populations from the South Pacific islands. Two groups were identified on the basis of susceptibility to the dengue virus: (1). populations with high infection rates, mostly the Ae. ae. aegypti form, and (2). mosquitoes with lower infection rates, specifically Ae. ae. formosus. Other evolutionary and epidemiological implications of the genetic variability of Ae. aegypti are also discussed.     

Suppression of Aedes aegypti by predatory Toxorhynchites moctezuma in an island habitat

Larval populations of the mosquito Aedes aegypti were suppressed by predatory Toxorhynchites moctezuma mosquito larvae released systematically in a village on Union Island (Saint Vincent and the Grenadines) during March-December 1988. Eggs and larvae of Tx.moctezuma were transported from Trinidad and introduced into all semi-permanent and permanent water-holding containers in the experimental village at Clifton. The semi-isolated village of Ashton served as control. Base-line Ae.aegypti indices (house, ovitrap, Breteau, cistern/tank, drum/barrel, small containers) were obtained for the two villages over a 4-month period prior to the introduction of the predatory Tx.moctezuma mosquito larvae. After sustained releases of predators for 5 months, all indices of Ae.aegypti were lower in the treated village than in the untreated village during the last 3 months of the year.     

Cultivation of mosquito cell lines in serum-free media and their effects on dengue virus replication

Seven mosquito cell lines from five species (Aedes aegypti, Ae. albopictus, Ae. pseudoscutellaris, Culex tarsalis, and Toxorhynchites amboinensis) were adapted to three kinds of serum-free media (SEM), which were composed of equal volumes of tryptose phosphate broth and of either Leibovitz (L15) medium, Eagle's minimum essential medium, or Medium 199 with Hanks' salts. Population growth rates of the cells cultivated in the SMFs were generally slower than those of original cell cultures maintained in conventional media containing bovine sera. A karyological study showed a significant shift to heteroploidy in two of the four cell lines examined. Four SMF-adapted sublines were compared with parental cultures for replication of dengue viruses. Ae. aegypti RML-12, Ae. albopictus C6/36, Ae. pseudoscutellaris AP-61, and Tx. amboinensis TRA-171 demonstrated different levels of alteration in virus replication ranging from lower titers (as in Ae. albopictus C6/36) to comparable or higher titers (as in Ae. aegypti RML-12) when they were simultaneously inoculated with four dengue serotypes.     

Aedes aegypti survival and dengue transmission patterns in French Guiana.

Field survival of Aedes aegypti females is a key parameter for estimating the dengue transmission potential of a mosquito population. The objectives of this study were to explore the dynamics of these survival rates at different times of the year in French Guiana and to analyze the results from the perspective of dengue patterns. The mosquitoes were captured, marked, released, and recaptured during four consecutive days in six houses every month, for three to 24 months, from January 1997 to December 1998. Laboratory experiments showed no effects on female survival but some effect on the survival of males. Females' daily survival in the field varied from 0.525 to 1 but was mostly between 0.8 and 0.95 during the entire year, with a mean value of 0.913. The field survival of Ae. aegypti females in French Guiana was thus in agreement with the likely transmission of dengue and the dengue endemic patterns throughout the year. On the other hand, heavy rainfalls during this time were less favorable to Ae. aegypti survival, which may explain part of the El Ni?o effect on dengue epidemics in French Guiana. The methods and results on Ae. aegypti survival will be implemented in a global dengue surveillance network in French Guiana.     

Preliminary data on the performance of Aedes aegypti and Aedes albopictus immatures developing in water-filled tires in Rio de Janeiro

A monthly survey of Aedes aegypti and Aedes albopictus immatures in discarded tires at a site in metropolitan Rio de Janeiro showed that Ae. albopictus was much more abundant in the rainy season, but Ae. aegypti abundance showed a less clear seasonal pattern. Pupal masses for Ae. albopictus showed a seasonal trend. In contrast, Ae. aegypti pupae did not show any clear trend in weight. Large Ae. albopictus pupae were found in the warmer months, when water volume was higher, pH lower and larval abundance lower. Further studies should be carried out to assess how seasonal variations in body size may impact vector competence of these species in Brazil.     

Seasonal profiles of Aedes aegypti (Diptera: Culicidae) larval habitats in an urban area of Costa Rica with a history of mosquito control

Dengue is the most important arboviral disease worldwide and the principal vector-borne disease in Costa Rica. Control of Aedes aegypti populations through source reduction is still considered the most effective way of prevention and control, although it has proven ineffective or unsustainable in many areas with a history of mosquito control. In this study, seasonal profiles and productivity of Aedes aegypti were analyzed in the city of Puntarenas, Costa Rica, where vector control has been practiced for more than ten years. Households contained more than 80% of larval habitats identified, although presence of habitats was more likely in other locations like lots and streets. In the wet season, habitats in the "other" category, like appliances, small manholes, and miscellaneous containers, were the most frequent habitats observed as well as the most common and productive habitats for Ae. aegypti. In the dry season, domestic animal drinking containers were very common, although concrete washtubs contained 79% of Ae. aegypti pupae collected. Individually, non-disposable habitats were as likely or more likely to contain mosquito larvae, and large containers were more likely to harbor mosquito larvae than the small ones only in the dry season. Considering various variables in the logistic regressions, predictors for Ae. aegypti in a habitat were habitat type (p < 0.001), setting (p = 0.043), and disposability (p = 0.022) in the wet season and habitat capacity in the dry season (p = 0.025). Overall, traditional Ae. aegypti larval indices and pupal indices in Puntarenas were high enough to allow viral transmission during the wet season. In spite of continued vector control, it has not been possible to reduce vector densities below threshold levels in Puntarenas, and the habitat profiles show that non-household locations, as well as non-disposable containers, should be targeted in addition to the standard control activities.