Differential predation of the planarian Dugesia tigrina on two mosquito species under laboratory conditions

Two experiments were performed on the predation of the planarian Dugesia tigrina (Girard) upon 2 mosquito prey species, Aedes albopictus and Culex quinquefasciatus. Bioassays were carried out in sectioned tires with 2 liters of water. In the 1st experiment, predation was evaluated using 4, 8, and 12 mature planarians against 40 2nd-stage larvae of each mosquito species alone. In the 2nd experiment, the same 3 predator densities were used with a pool composed of 20 2nd-stage larvae of each mosquito species. In the 1st experiment, final corrected mortality of Ae. albopictus reached 89.1, 98.8, and 99.6% and final corrected mortality of Cx. quinquefasciatus reached 29.4, 48.0, and 53.0%, respectively, with 4, 8, and 12 planarians. In the 2nd experiment and when subjected to the density of 4 planarians, Ae. albopictus was more susceptible to predation, with a selectivity index of 0.87, whereas this index was 0.13 for Cx. quinquefasciatus. Predation was more intensive during the 1st 4 days of the experiments, when most larvae were in the 2nd and 3rd stages. We observed that Cx. quinquefasciatus larvae were faster than Ae. albopictus in reacting to planarian contacts, resulting in more success in escaping from the predator attacks.     

Prey-predator relationship between the cyclopoids Mesocyclops longisetus and Mesocyclops meridianus with Anopheles aquasalis larvae

Copepods from the genus Mesocyclops are considered predators and potential biological control for mosquito larvae. Two copepod species M. meridianus and M. longisetus were found in natural developmental habitat for malaria vector Anopheles aquasalis in Paria, Venezuela. Predatory potential on 1st-stage mosquito larvae An. aquasalis was evaluated under laboratory conditions for the 2 species of copepod. Further records of both copepod life cycle and body size were taken. A 2 x 3 factorial design was used, consisting of 1:1 and 10:1 prey-predator ratios with and without interspecific interactions. Despite significant body-size differences, M. longisetus and M. meridianus reached maturity 17 days after hatching with no significant differences. Life cycle span of both copepod species are described for the first time. The 2 species showed the same predatory potential despite larval (prey) abundance variation.     

Laboratory determination of efficacy of a Santalum spicatum extract for mosquito control

The activity of QN50, a sequiterpene alcohol derived from Australian sandalwood (Santalum spicatum), was tested for its effectiveness against larvae of 2 mosquito species (Culex molestus and Aedes camptorhynchus [Diptera: Culicidael), nymphs of 2 species of water boatmen (Micronecta robusta and Agraptocorixa [Hemiptera: Corixidae]), immature Daphnia sp. (Crustacea), and mosquito eggs (Cx. molestus). In a series of laboratory bioassays, field-collected mosquito larvae, eggs, and immature corixids and daphnids were placed in beakers with either QN50, methoprene or source water only (control). The mosquito larvae exposed to QN50 had reduced survivorship and average longevity relative to the control and to methoprene at most concentrations used in this study. The hatching rate of mosquito eggs was unaffected by methoprene or QN50. Corixid nymphs and daphnids experienced high mortality in both methoprene and QN50 relative to the control, but there was no difference in the effect between the compounds. The results of this preliminary study suggest that further research into the mode of action and efficacy of QN50 as a potential alternative to methoprene for mosquito abatement is warranted.     

Prey-size selection by Triops longicaudatus (Notostraca: Triopsidae) feeding on immature stages of Culex quinquefasciatus

The tadpole shrimp, Triops longicaudatus, was found to be a size-dependent predator of Culex quinquefasciatus larvae in the laboratory. However, changes in tadpole shrimp size were accompanied by changes in prey-size preference: larger-sized predators consumed an increasing proportion of larger prey items. Very large tadpole shrimp may be nonselective predators of this mosquito species. Quantified behavioral observations indicated that while second instar mosquito larvae were encountered significantly less frequently than were fourth instar larvae or pupae, they were captured at significantly greater rates and with shorter handling times. It is hypothesized that prey vulnerability has an important influence on tadpole shrimp prey size "preferences."     

Analysis of the gut contents of naiads of Enallagma civile (Odonata: Coenagrionidae) from a Texas pond

Foregut contents of naiads of the damselfly species, Enallagma civile, collected from a permanent pond, were analyzed to determine the natural prey for immatures of this species. The analyses revealed the naiads containing prey had fed predominantly on chironomid larvae. Corixid, cladoceran, ostracod and aquatic mite remains were found in some of the naiad specimens examined. However, no remains of mosquito larvae were detected in any of the specimens, even though mosquito larvae were observed as being continuously present in the pond sites where the naiad specimens were collected.     

A laboratory study of predation by damselfly nymphs, Enallagma civile, upon mosquito larvae, Culex tarsalis

The nymph of the damselfly, Enallagma civile, feeds on the larvae of the mosquito Culex tarsalis amongst a variety of other small aquatic invertebrates. Average daily consumption of 3rd instar Cx. tarsalis larvae by the last nymphal stage of E. civile was 6.06 larvae (range 4.64-8.67). Experiments in which density of prey (mosquito larvae) and predators (E. civile nymphs) were varied, showed that more prey was consumed as prey density increased. However, fewer prey were consumed at higher predator densities; mutual interferences among predators at higher predator densities was suspected.     

Laboratory evaluation of the effect of alternative prey and vegetation on predation of Culex annulirostris immatures by Australian native fish species

The impact of alternative prey and simulated vegetation on Culex annulirostris Skuse predation efficacy by Australian smelt, Retropinna semoni (Retropinnidae); crimson-spotted rainbowfish, Melanotaenia duboulayi (Melanotaeniidae); empire gudgeon, Hypseleotris compressa (Eleotridae); estuary perchlet, Ambassis marianus (Ambassidae); firetail gudgeon, Hypseleotris galii (Eleotridae); fly-specked hardyhead, Craterocephalus stercusmuscarum (Atherinidae); and Pacific blue-eye, Pseudomugil signifer (Atherinidae), was evaluated in Queensland, Australia. The presence of chironomid midge larvae and tusked frog, Adelotus brevis (Leptodactylidae), tadpoles did not have a significant negative impact on the predation rates of Cx. annulirostris by these 7 fish species. Hypseleotris galii, M. duboulayi, and R. semoni demonstrated strong preference for larvae of Cx. annulirostris over both alternative prey species. In the presence of alternative prey species, the mean predation rate of M. duboulayi on larvae of Cx. annulirostris remained greater than that of other fish species tested. When evaluated at varying densities of simulated vegetation, predation rates of all fish species were similar to those reported in open conditions.     

Chronic effects of Cd on the reproduction of the guppy (Poecilia reticulata) through Cd-accumulated midge larvae (Chironomus yoshimatsui)

Chronic effects of Cd on the growth and reproduction of the guppy (Poecilia reticulata) were studied using a food chain model, midge larvae as prey and guppy as predator. The transfer rate of Cd from the midge to the guppy was between 0.5 and 1% during the 30-day experiment. Growth rate of the guppy fed Cd-accumulated midge larvae (270 micrograms/g dry wt) for 30 days was not impaired. Cumulative numbers of fry produced by the guppy fed Cd-accumulated midge larvae (210 micrograms/g) for 2 months decreased to ca. 80% of the control. Guppies had been fed the Cd-accumulated midges from 30 days old for 7 months. Cumulative numbers of fry produced by the guppy fed midge larvae-accumulated 500, 800, and 1,300 micrograms Cd/g for 6 months decreased to 79, 65, and 55% of the control, respectively. Similar effects of Cd on the reproduction of guppy were shown between the guppies fed the Cd-accumulated midge larvae (500 micrograms Cd/g) and exposed to 10 or 20 micrograms Cd/liter for the 6 months. The Cd concentrations of the digestive tract, liver, and kidney increased strongly, indicating that such Cd accumulation was brought on mainly through the Cd-accumulated midges. Mortality of the female guppies fed larvae-accumulated 1,300 micrograms Cd/g increased abruptly from the 6 months of the experiment, whereas no male guppy died during the experiment.     

The effectiveness of Mesocyclops longisetus (Copepoda) for the control of container-inhabiting mosquitoes in residential environments

The cyclopoid crustacean Mesocyclops longisetus was evaluated for its predatory potential to reduce container-inhabiting mosquitoes in 5 suburban Florida backyards. Aedes albopictus, Ae. triseriatus, and Culex quinquefasciatus were the predominant species collected from containers. At an initial inoculation rate of approximately 120 copepods per container, M. longisetus populations eliminated resident mosquito larvae for a minimum of 14 wk in 30-liter plastic buckets and up to 29 wk in 0.4-liter ceramic flowerpots and 0.3-liter glass jars depending on species. Copepod populations generally peaked 13 wk after introduction (August) in ceramic flowerpots and glass jars and about 1 month later in tires, plastic buckets, and plastic flowerpots. At the time of peak abundance, average predator numbers ranged between 900 (glass jar) to >3000 (30-liter bucket) individuals per container. Although all mosquito species were eliminated from all containers sometime during the 35-wk study, M. longisetus appeared to preferably prey on Aedes larvae compared with Culex. Operationally, the use of M. longisetus as a tool for control of container-inhabiting mosquitoes in urban/suburban settings proved to be relatively inexpensive, required little labor for colony maintenance, was easily transported, and easily applied.     

Rift Valley fever virus (family Bunyaviridae, genus Phlebovirus). Isolations from Diptera collected during an inter-epizootic period in Kenya

A total of 134 876 Diptera collected in Kenya during a 3-year period were tested in 3383 pools for Rift Valley fever (RVF) virus. Nineteen pools of unengorged mosquitoes were found positive for RVF. All isolations were made from specimens collected at or near the naturally or artificially flooded grassland depressions that serve as the developmental sites for the immature stages of many mosquito species. The isolation of virus from adult male and female A. lineatopennis which had been reared from field-collected larvae and pupae suggests that transovarial transmission of the virus occurs in this species.     

Rift Valley fever virus (family Bunyaviridae, genus Phlebovirus). Isolations from Diptera collected during an inter-epizootic period in Kenya.

A total of 134 876 Diptera collected in Kenya during a 3-year period were tested in 3383 pools for Rift Valley fever (RVF) virus. Nineteen pools of unengorged mosquitoes were found positive for RVF. All isolations were made from specimens collected at or near the naturally or artificially flooded grassland depressions that serve as the developmental sites for the immature stages of many mosquito species. The isolation of virus from adult male and female A. lineatopennis which had been reared from field-collected larvae and pupae suggests that transovarial transmission of the virus occurs in this species.     

Colonization of Culex nigripalpus theobald (Diptera: Culicidae) by stimulation of mating using males of other mosquito species.

Culex nigripalpus Theobald (Diptera: Culicidae) was recolonized successfully by cohabiting Aedes taeniorhynchus males or males of other mosquito species starting in a large outdoor cage under natural light-dark cycles and temperatures and ending in a 1-ft.3 cage under artificial light-dark cycles at 24 degrees C without added stimulation.     

Evaluation of vegetation management strategies for controlling mosquitoes in a southern California constructed wetland

The abundance of mosquito larvae and adult production were measured in 3 vegetation treatments and 2 species of emergent macrophytes in replicated wetland mesocosms (12 x 80 m). During the 8-wk study, no significant differences were found in abundances of larvae and emerging adult mosquitoes among the vegetation treatments: 100% of the surface area in emergent vegetation, 50% of the surface area in emergent vegetation in 5-m-wide rows, and 50% of the surface area in emergent vegetation in 10-m-wide rows. Mosquito larvae (predominantly Culex tarsalis and Anopheles hermsi) were significantly more abundant in inundated bulrush (Schoenoplectus californicus) than in inundated cattail (Typha sp.). Adult emergence from vegetated zones containing bulrush also was significantly greater than from cattail. The failure of reduced emergent vegetation coverage to provide a significant reduction in mosquito production from the vegetated zones of the wetlands might have been caused by favorable conditions for mosquito oviposition and larval development after vegetation management and by the ineffectiveness of mosquito predators in emergent vegetation. A 50% reduction of vegetation did not significantly reduce the water quality of the wetland effluent; however, narrower rows (<5 m wide) of vegetation may be required to reduce mosquito production from vegetated regions of the treatment wetlands. Even though the abundance of mosquito larvae in open water is typically less than in emergent vegetation, creation of open-water zones in shallow treatment wetlands (<1 m depth) by drying the wetland followed by removal of emergent vegetation with heavy equipment is unlikely to provide a significant long-term reduction of mosquito production.     

Susceptibility of Aedes aegypti larvae to parasitism by Romanomermis culicivorax in laboratory and field conditions in Oaxaca, Mexico]

In June 1996 in the state of Oaxaca, Mexico, larvae of the mosquito species Aedes aegypti were exposed to infective preparasites of the nematode Romanomermis culicivorax, Ross and Smith, in the laboratory and in the field. For the laboratory experiments larvae in instars I-IV were used; they had been collected in natural reservoirs. The laboratory experiments were carried out in triplicate, with 100 larvae of each larval stage per experiment. Three preparasite application dosage ratios were tested: 5, 10, or 15 preparasites per mosquito larva. For the field studies 13 A. aegypti outdoor breeding sites were used, with larvae in instars I-IV and a 15:1 preparasite dosage ratio. With the laboratory experiments, an increase was observed in the average infestation of the larvae as the preparasite application ratio was increased from 5:1 to 15:1. With a 10:1 ratio, the rates of parasitism were 100%, 100%, 85%, and 74% in the larvae in instars I, II, III, and IV, respectively; for the 15:1 preparasite ratio, parasitism rates were 100%, 100%, 90%, and 79%, respectively. The field tests with the 15:1 preparasite dosage ratio in the 13 outdoor reservoirs produced parasitism rates of 80% to 98%, thus demonstrating the susceptibility of this species of mosquito to parasitism by R. culicivorax in Oaxaca, Mexico.     

Toxicity and bioaccumulation of fipronil in the nontarget arthropodan fauna associated with subalpine mosquito breeding sites

In order to examine ecological impact of fipronil use for larval culicine control in natural hydrosystems, toxicity and bioaccumulation of this new insecticide were analyzed on aquatic species representative of the nontarget arthropodan fauna (nonculicine larval Diptera: Chaoboridae, Chironomidae; planktonic Crustacea: Cladocera, Copepoda, Ostracoda) associated with target larval mosquito populations in the subalpine breeding sites. Standard toxicological bioassays using fipronil aqueous solutions from 1 to 2000 nM indicated different sensitivity levels among species. Insecticide bioaccumulation analyses, using [(14)C]fipronil solutions in simplified laboratory ecosystem, also indicated large differences among species. These differences may come from biological parameters characteristic of each species. Taking into account these nontarget effects of fipronil, a possible strategy of use of this insecticide for integrated mosquito control management was proposed, which is based upon selective dietary absorption of the insecticide by larval Culicidae.     

Perspectives on management of pestiferous Chironomidae (Diptera), an emerging global problem

In recent years, adult Chironomidae emerging from some urban natural or man-made habitats have increasingly posed a variety of nuisance and economic problems, and in some situations medical problems to humans in different parts of the world. Although there are an estimated 4,000 or more species of chironomid midges worldwide, less than 100 species have been reported to be pestiferous. Among midge control methods, numerous laboratory and field studies have been conducted on the use of organochlorines, organophosphates (OPs), pyrethroids and insect growth regulators (IGRs). Field use of OP insecticides such as chlorpyrifos, temephos and others in the USA and Japan has generally resulted in larval control for 2-5 wk or longer with application rates below 0.56 kg AI/ha (USA) and less than 1-5 ppm (Japan). Frequent use of some OP insecticides in the USA and Japan has caused their increased tolerance in several midge species. The IGRs, diflubenzuron and methoprene, provide alternate means for midge control. These IGRs in some situations suppressed adult midge emergence by greater than 90% at rates less than 0.3 kg AI/ha. A number of parasites and pathogens have been reported from midges in different parts of the world. Bacillus thuringiensis serovar. israelensis is effective against some midge species, but at rates at least 10x or higher established for mosquito larvicidal activity. The flatworm, Dugesia dorotocephala, and some fish species offer a good potential for midge control in some situations. In large habitats covering hundreds or thousands of ha, information on the basic ecology of larval midges and adult behavior is essential for formulating midge control criteria. More research is needed on the biological and physical and cultural control of these pestiferous insects.     

Trace Metal Levels in Chironomid Larvae and Sediments from a Bolivian River: Impact of Mining Activities

The effect of mining activity on metal accumulation in sediments and Chironomidae in a river in Bolivia was assessed. Surficial sediments and midge larvae (Chironomidae, Diptera) were collected at five sampling sites. Concentrations of the trace metals Cd, Cu, Cr, Ni, Pb, and Zn were measured in organisms and sediments by inductively coupled plasma atomic emission spectrometry. Sediments were subjected to two different extraction procedures to identify total trace metals and reducible trace metals. Geochemical characteristics of the sediment were analyzed: total organic carbon (TOC), Fe and Mn oxides, and particle size distribution. To determine the relative importance of the different sediment factors contributing to the variation in metal accumulation by the chironomid larvae, nonlinear regression models were constructed. No increase in metal concentration in sediment could be measured downstream of the mining activity. Larval concentrations, however, increased markedly. Only for zinc and chromium was a significant amount of variation (48 and 73%, respectively) found. The lack of relationship for the other metals probably was due to a unmeasured exposure route, the overlying water.     

Mansonia dyari, Mansonia flaveola and Aedeomyia squamipennis in the Dominican Republic, three new country records

We report the first collection of 3 mosquito species representing 2 genera in the Dominican Republic. The collections of adults and larvae of Mansonia dyari Belkin, Heinemann, and Page and Mansonia flaveola (Coquillett) from Santo Domingo City represent 2 additional mosquito species to the mosquito fauna of the Dominican Republic. Larvae were collected in the Quitasueno and Puerta de Hierro lagoons (covered with the Pistia stratiotes plants) in Santo Domingo. The associated species Aedeomyia squamipennis Lynch Arribalzaga was also collected for the first time and is the only representative of the genus Aedeomyia Theobald in the Dominican Republic. These collections increase the number of mosquito species belonging to the Genus Mansonia from 1 to 3 and total species from 45 to 48 in the Dominican Republic.     

Habitat characteristics of larval mosquitoes in zoos of South Carolina, USA

To investigate whether the unique assemblage of habitats in zoos could affect mosquito oviposition behavior and to provide zoos with suggestions for mosquito control, larvae were sampled and associated habitat variables were measured in 2 zoos in South Carolina, U.S.A. Fifty-nine sites were sampled from March 2008 to January 2009. A total of 1630 larvae representing 16 species was collected and identified. The dominant species was Aedes albopictus (46.0%), followed by Ae. triseriatus (23.6%), Culex restuans (12.4%), and Cx. pipiens complex (9.7%). Principal components and multiple logistic regression analyses showed that across both zoos the distribution of Ae. albopictus larvae was predicted by ambient and site temperature, precipitation, dissolved oxygen, and container habitats. The distribution of Ae. triseriatus larvae was predicted by natural containers and shade height < or =2 m. Overall larval mosquito presence (regardless of species) was predicted by ambient and site temperature, precipitation, dissolved oxygen, presence of natural habitats, and absence of aquatic vegetation. Additionally, C8 values of pairwise species associations indicated significant habitat-based relationships between Ae. albopictus and Ae. triseriatus, and Cx. pipiens complex and Cx. restuans. In general, species-habitat associations conformed to previously published studies. Recommendations to zoo personnel include elimination of artificial container habitats, reduction of shade sources < or =2 m over aquatic habitats, use of approved mosquito larvicides, and training in recognizing and mitigating larval mosquito habitats.