Oviposition attractancy of bacterial culture filtrates: response of Culex quinquefasciatus

Mitigating the Public Health Issues Caused by the Filarial Vector, Culex quinquefasciatus (Diptera: Culicidae) Through Phytocontrol and Larval Source Marker Management

Failure of conventional mosquito control strategies to curb the population of vectors have made the humans vulnerable to serious medical problems transmitted by them. This effect has been compounded by global climate change enabling the mosquitoes to cross geographical boundaries and cause trouble in regions where they were initially not found. As such, the scientific community has been compelled to devise alternative and innovative strategies of mosquito control that can be integrated with the conventional practices to implement multi-phasic approach of vector management. Culex quinquefasciatus is one such mosquito species that is reported to be one of the primary vectors of lymphatic filariasis and many other diseases of global health concern. However, not much is known about its breeding habitat ecology and microbial properties that have enabled the species to achieve reproductive success in urbanized habitats. The current investigation was carried out at Digha, West Bengal, India. The region, despite being endemic for lymphatic filariasis, has rarely been explored for its mosquito diversity and/or their breeding habitat characteristics. Therefore, these were attempted. For survey and sampling, seven villages were chosen, namely, Duttapur, Jatimati, Champabani, Padima, Gobindabasan, Bhagibaharampur and Palsandapur. The study showed that Cx. quinquefasciatus is the dominant mosquito species at the sampling sites with the highest density of their larvae being recorded from man-made structures like drains and pools close to human habitations and livestock. The study was, therefore, restricted to Cx. quinquefasciatus. Seasonal abundance showed that they were most prevalent in the monsoon followed by summer. The physicochemical characterization showed their larvae to prefer almost neutral pH (6.9 to 7.3), low chloride concentration (98 to 258 ppm) and turbidity. As far as other parameters are concerned, they were tolerant towards a wide range allowing them to adapt varied habitats in the study areas. The bacterial profiling of their natural habitat waters revealed the presence of Paenibacillus nanensis DGX1(OQ690670), Bacillus cereus DGX2(OQ690675), Bacillus sp. DGX3(OQ690700) and Escherichia coli DGX4(OQ690701). Bacillus cereus was found to have high oviposition attractant properties in oviposition assays. Bacillus cereus was also obtained from the midgut of third instar larvae indicating that they had entered from the surrounding medium and colonized the larval gut. Subsequent tests exhibited the roles of B. cereus in larval development. Numerous plant products have been reported either as insecticides for killing larvae or adult mosquitoes or as repellents for mosquito biting and the best alternatives for mosquito control. Larvicidal potential of emulsified neem oil formulation against the field collected 3rd instar larvae of Culex quinquefasciatus mosquito under laboratory conditions was also evaluated. The information thus obtained can be pooled to generate larval source markers and larval source management practices by altering their habitats that cannot be removed. Furthermore, the time of implementation of these strategies can also be planned.

Evaluation of indigenous plants' extracts for mosquitocidal activity against different stages of Culex quinquefasciatus say (Diptera: Culicidae)

Being vector of West Nile Virus and falariasis the control of Culex quinquefasciatus is likely to be essential. Synthetic insecticide treatment is looking most effective for vectors mosquito control. However, these products are toxic to the environment and non-target organisms. Consequently, ecofriendly control of vectors mosquito is needed. In this regard botanical insecticide is looking more fruitful. Therefore, the present research aimed to investigate the effectiveness of methanolic extract and various fractions, including, n-hexane, ethyl-acetate, chloroform, and aqueous fraction, obtained from methanolic extract of Ailanthus altissima, Artemisia scoparia, and Justicia adhatoda using separating funnel against larval, pupal, and adult stages of Culex quinquefasciatus. The larvae and pupae of Culex quinquefasciatus were exposed to various concentrations (31.25-1000 ppm) of methanolic extract and its fractions for 24 hours of exposure period. For knock-down bioassay (filter paper impregnation bioassay) different concentration of the methanolic extract and its various fractions (i.e. 0.0625, 0.125, 0.25, 0.5 and 1mg/mL) were applied for 1 hour exposure period. The results were statistically analysed using standard deviation, probit analysis, and linear regression. The R2 values of larvae, pupae, and adult range from 0.4 to 0.99. The values of LC50 (concentration causing 50% mortality) for late 3rd instar larvae after 24 hours exposure period range from 93-1856.7 ppm, while LC90 values range from 424 -7635.5ppm. The values of LC50for pupae range form 1326.7-6818.4ppm and and values of LC90 range from 3667.3-17427.9ppm, respectively. The KDT50 range from 0.30 to 2.8% and KDT90 values range from1.2 to 110.8%, respectively. In conclusion, Justicia adhatoda may be effective for controlling populations of vector mosquito.

Exploiting the chemical ecology of mosquito oviposition behavior in mosquito surveillance and control: a review

Vector control is an important component of the interventions aimed at mosquito-borne disease control. Current and future mosquito control strategies are likely to rely largely on the understanding of the behavior of the vector, by exploiting mosquito biology and behavior, while using cost-effective, carefully timed larvicidal and high-impact, low-volume adulticidal applications. Here we review the knowledge on the ecology of mosquito oviposition behavior with emphasis on the potential role of infochemicals in surveillance and control of mosquito-borne diseases. A search of PubMed, Embase, Web of Science, Global Health Archive, and Google Scholar databases was conducted using the keywords mosquito, infochemical, pheromone, kairomone, allomone, synomone, apneumone, attractant, host-seeking, and oviposition. Articles in English from 1974 to 2019 were reviewed to gain comprehensive understanding of current knowledge on infochemicals in mosquito resource-searching behavior. Oviposition of many mosquito species is mediated by infochemicals that comprise pheromones, kairomones, synomones, allomones, and apneumones. The novel putative infochemicals that mediate oviposition in the mosquito subfamilies Anophelinae and Culicinae were identified. The role of infochemicals in surveillance and control of these and other mosquito tribes is discussed with respect to origin of the chemical cues and how these affect gravid mosquitoes. Oviposition attractants and deterrents can potentially be used for manipulation of mosquito behavior by making protected resources unsuitable for mosquitoes (push) while luring them towards attractive sources (pull). In this review, strategies of targeting breeding sites with environmentally friendly larvicides with the aim to develop appropriate trap-and-kill techniques are discussed.

Rat volatiles as an attractant source for the Asian tiger mosquito, Aedes albopictus

Aedes albopictus is a vector of dengue, chikungunya, and dirofilariasis. Volatile compounds are crucial for mosquitoes to locate their hosts. This knowledge has allowed the identification of attractants derived from human odours for highly anthropophilic mosquito species. In this study, we used rats as a experimental model to identify potential attractants for host-seeking Ae. albopictus females. Porapak Q extracts from immature female rats were more attractive to Ae. albopictus females than those from mature and pregnant females, and males. Phenol, 4-methylphenol, 4-ethylphenol, and indole were identified compounds in male, immature, mature, and pregnant female extracts. There were quantitative differences in these compounds among the extracts that likely explain the discrepancy in their attractiveness. Ae. albopictus females were not attracted to the single compounds when was compared with the four-component blend. However, the binary blend of 4-methylphenol  + 4-ethylphenol and the tertiary blend of 4-methylphenol + 4-ethylphenol + indole were as attractive as the four-component blend. In the field trials, BGS traps baited with the tertiary or quaternary blends caught more Ae. albopictus females and males than BGS traps without lures. This is the first laboratory and field study to identify compounds that mediate the attraction of Ae. albopictus to one of its hosts.

Behavioral responses of gravid Culex quinquefasciatus, Aedes aegypti, and Anopheles quadrimaculatus mosquitoes to aquatic macrophyte volatiles

Mosquitoes use many cues to assess whether a habitat is conducive for reproduction, possibly including the presence of stimuli from aquatic macrophytes. The effect of water infusions of water hyacinth (Eichhornia crassipes), water lettuce (Pista stratioles), parrotfeather (Myriophyllum aquaticum), and water pennywort (Hydrocotyle umbellata) on mosquito oviposition and attraction was investigated. Gravid Culex quinquefasciatus deposited significantly more egg rafts in water hyacinth, water lettuce, or Bermuda hay (positive control) infusions compared to water, while water pennywort and parrotfeather infusions did not differ from water. In-flight attraction responses of Cx. quinquefasciatus, Aedes aegypti, and Anopheles quadrimaculatus were evaluated. The strongest attraction of gravid Cx. quinquefasciatus and Ae. aegypti occurred in the presence of volatiles from infusions of water hyacinth and water lettuce, which were equal in attractiveness to hay infusion. Water pennywort and parrotfeather infusions were not attractive. Gravid An. quadrimaculatus were not attracted to aquatic plant volatiles. The results suggest that water hyacinth and water lettuce emit volatile chemicals that attract two of three mosquito species tested and stimulate oviposition by Cx. quinquefasciatus, demonstrating that the level of attraction of aquatic plant volatiles varies among species in ways that may have relevance to bait-based detection and control methods.

Oviposition responses of Aedes mosquitoes to bacterial isolates from attractive bamboo infusions

Background

The mosquitoes Aedes aegypti and Aedes albopictus are vectors of pathogenic viruses that cause major human illnesses including dengue, yellow fever and chikungunya. Both mosquito species are expanding their geographic distributions and now occur worldwide in temperate and tropical climates. Collection of eggs in oviposition traps (ovitraps) is commonly used for monitoring and surveillance of container-inhabiting Aedes populations by public health agencies charged with managing mosquito-transmitted illness. Addition of an organic infusion in these traps increases the number of eggs deposited. Gravid females are guided to ovitraps by volatile chemicals produced from the breakdown of organic matter by microbes.

Methods

We previously isolated and cultured 14 species of bacteria from attractive experimental infusions, made from the senescent leaves of canebrake bamboo (Arundinaria gigantea). Cultures were grown for 24 h at 28 °C with constant shaking (120 rpm) and cell densities were determined with a hemocytometer. Behavioral responses to single bacterial isolates and to a mix of isolates at different cell densities were evaluated using two-choice sticky-screen bioassay methods with gravid Ae. aegypti and Ae. albopictus.

Results

In behavioral assays of a mix of 14 bacterial isolates, significantly greater attraction responses were exhibited by Ae. aegypti and Ae. albopictus to bacterial densities of 10⁷ and 10⁸ cells/mL than to the control medium. When we tested single bacterial isolates, seven isolates (B1, B2, B3, B5, B12, B13 and B14) were significantly attractive to Ae. aegypti, and six isolates (B1, B5, B7, B10, B13 and B14) significantly attracted Ae. albopictus. Among all the isolates tested at three different cell densities, bacterial isolates B1, B5, B13 and B14 were highly attractive to both Aedes species.

Conclusions

Our results show that at specific cell densities, some bacteria significantly influence the attraction of gravid Ae. aegypti and Ae. albopictus females to potential oviposition sites. Attractive bacterial isolates, when formulated for sustained release of attractants, could be coupled with an ovitrap containing a toxicant to achieve area-wide management of Aedes mosquitoes.

Preliminary evaluation of a nonanal lure for collection of gravid Culex quinquefasciatus

Gravid traps are important tools for disease monitoring and for research on mosquito ovipositional behavior. Two experiments were conducted to evaluate a 2% nonanal lure in gravid mosquito traps in Ifakara, Tanzania. The 1st experiment focused on whether water was needed in the pan below the trap for the nonanal lure to be effective. There was no significant difference between the numbers of gravid females of Culex quinquefasciatus collected in traps using a nonanal lure either with or without water. The 2nd experiment compared the lure, without water, to a grass infusion and a blank trap, without water or attractant. Significantly more mosquitoes were collected in traps with grass infusion than in traps with the other attractants, which were not significantly different from each other. Although more mosquitoes were collected in traps with grass infusion, substantial numbers were also collected in traps with the nonanal lure and unbaited traps.

Evaluation of a nonanal-trimethylamine lure for collection of Culex quinquefasciatus (Diptera: Culicidae) in gravid traps

Gravid traps are useful tools for monitoring vector-borne pathogens in mosquitoes, particularly for those pathogens transmitted by Culex quinquefasciatus Say. One of the primary challenges in the use of gravid traps is the necessity of the inclusion of an oviposition attractant, usually an infusion of organic material, which changes in attractiveness over time. However, a standardized lure, using nonanal and trimethylamine (N + TMA), has been developed and is commercially available. The N + TMA lure was tested against grass infusion and tap water in Tanzania, where Cx. quinquefasciatus is a vector of lymphatic filariasis. Traps baited with grass infusion collected significantly more mosquitoes than N + TMA-baited traps, which collected significantly more than traps baited with tap water. The advantages and disadvantages of the standardized lure are discussed.

Monitoring temporal fluctuations of Culex quinquefasciatus using oviposition traps containing attractant and larvicide in an urban environment in Recife, Brazil

The use of attractants and larvicides in oviposition traps is of practical interest for the surveillance and control of urban mosquitoes. In addition to increasing the safety of the traps, this combination is essential for an attract-and-kill control strategy based on trapping mosquito eggs. The combination of Bacillus thuringiensis var. israelensis (Bti) and grass infusion (GI) vs. GI alone were tested for their ability to attract in paired BR-OVT traps in the backyards of 10 houses in Recife, Brazil, for a period of 45 days. Results show that females prefer to oviposit in traps containing Bti (363 compared with 251 egg rafts over 45 days). Results from a one-year trial on the efficacy of BR-OVT traps loaded with GI and Bti as a sampling tool to monitor temporal fluctuations in the population densities of Culex quinquefasciatus in an urban environment are also reported. From December 2006-January 2007, one trap per home was installed and maintained for 348 consecutive days in 134-151 houses located in three urban blocks. Throughout the one-year field trial a total of 43,151 Culex egg rafts were collected in the traps. The data show that BR-OVT loaded with GI and Bti is sensitive enough to demonstrate continuous reproductive activity of Cux. quinquefasciatus in the study area throughout the year and to monitor temporal fluctuations in population density.

Proteus mirabilis interkingdom swarming signals attract blow flies

Flies transport specific bacteria with their larvae that provide a wider range of nutrients for those bacteria. Our hypothesis was that this symbiotic interaction may depend on interkingdom signaling. We obtained Proteus mirabilis from the salivary glands of the blow fly Lucilia sericata; this strain swarmed significantly and produced a strong odor that attracts blow flies. To identify the putative interkingdom signals for the bacterium and flies, we reasoned that as swarming is used by this bacterium to cover the food resource and requires bacterial signaling, the same bacterial signals used for swarming may be used to communicate with blow flies. Using transposon mutagenesis, we identified six novel genes for swarming (ureR, fis, hybG, zapB, fadE and PROSTU_03490), then, confirming our hypothesis, we discovered that fly attractants, lactic acid, phenol, NaOH, KOH and ammonia, restore swarming for cells with the swarming mutations. Hence, compounds produced by the bacterium that attract flies also are utilized for swarming. In addition, bacteria with the swarming mutation rfaL attracted fewer blow flies and reduced the number of eggs laid by the flies. Therefore, we have identified several interkingdom signals between P. mirabilis and blow flies.

Stability, oviposition attraction, and larvicidal activity of binary toxin from Bacillus sphaericus expressed in Escherichia coli

Bacillus sphaericus produces a two-chain binary toxin composed of BinA (42 kDa) and BinB (51 kDa), which are deposited as parasporal crystals during sporulation. The toxin is highly active against Culex larvae and Aedes and Anopheles mosquitoes, which are the principal vectors for the transmission of malaria, yellow fever, encephalitis, and dengue. The use of B. sphaericus and Bacillus thuringiensis in mosquito control programs is limited by their sedimentation in still water. In this study, the binA and binB genes were cloned and the recombinant BinAB protein was expressed in three strains of Escherichia coli. These recombinant strains were used in a toxicity assay against Culex quinquefasciatus larvae. The highest expression level was achieved when both proteins were expressed in a single operon construct. The BinAB protein expressed in the E. coli Arctic strain showed higher larvicidal activity than either of the recombinant proteins from the E. coli Ril or pLysS strains. Furthermore, it had the highest oviposition attraction (49.1%, P < 0.05). These data suggest that biologically active recombinant BinA and BinB toxins might be useful in mosquito control programs, delivered by inactivated bacterial cells or in traps.

MAP kinase cell signaling pathway as biomarker of environmental pollution in the sponge Suberites domuncula

In the present study, we analyzed the effects of two major pollutants of the environment, tributyltin (TBT) and water-accommodated fraction (WAF) of diesel oil, on MAP kinase activation, apoptosis induction and DNA damage, in the marine sponge Suberites domuncula. Our results clearly demonstrated a differential activation of the MAPKs depending on the chemicals tested. TBT induced the activation of p38 and JNK while diesel oil enhanced activation of both ERK and p38. The activation of MAPKs was observed after 1 h exposure and 6 and 24 h of recovery in seawater. In addition, DNA fragmentation, assessed by two techniques, the Fast micromethod(®) and the TUNEL assay, was detected after sponges were treated with both chemicals. Moreover, the study of caspase 3/7 activity showed that apoptosis was induced and triggered with all concentrations of TBT but only at high diesel oil concentrations. After TBT exposure, a correlation was observed between JNK activation, caspase 3 activity and DNA damage while p38 activation followed the two latter parameters at high concentrations of diesel oil, suggesting that sponges enhanced a specific apoptotic pathway depending on the xenobiotic tested. This study demonstrated a high signal response by the sponge Suberites domuncula to the tested chemicals. Cell signaling pathway studies may thus be of use in water quality biomonitoring programs.

Comparative responses of ovipositing Anopheles gambiae and Culex quinquefasciatus females to the presence of Culex egg rafts and larvae

Field observations have demonstrated that gravid Anopheles gambiae Giles s.s. (Diptera: Culicidae) are selective in their choice of oviposition sites. For example, immature stages of An. gambiae s.s. are rarely found in water that contains Culex quinquefasciatus Say immatures. The possibility that this may, in part at least, reflect a response by ovipositing An. gambiae s.s. females to volatile signals associated with Culex juveniles was evaluated by testing the response of An. gambiae s.s. females to varying densities of Cx. quinquefasciatus egg rafts and/or larvae in oviposition choice assays. For comparison, the oviposition choices of Cx. quinquefasciatus to conspecific egg rafts and/or larvae were similarly assayed. At a low density of Cx. quinquefasciatus egg rafts (1-15 egg rafts/100 mL water), An. gambiae s.s. females laid more eggs in the treatment water than in the control, with a maximum of twice as many in the treatment water at 5 egg rafts/100 mL water. At higher egg raft densities and in all treatments that included Cx. quinquefasciatus larvae, oviposition decreased significantly in the treatment dishes in a density-dependent manner. As previous studies have indicated, ovipositing Cx. quinquefasciatus females were attracted to and laid egg rafts in dishes containing conspecific egg rafts and, interestingly, also in dishes containing larvae.

Conservation of indole responsive odorant receptors in mosquitoes reveals an ancient olfactory trait

Aedes aegypti and Anopheles gambiae are among the best-characterized mosquito species within the Culicinae and Anophelinae mosquito clades which diverged ∼150 million years ago. Despite this evolutionary distance, the olfactory systems of these mosquitoes exhibit similar morphological and physiological adaptations. Paradoxically, mosquito odorant receptors, which lie at the heart of chemosensory signal transduction pathways, belong to a large and highly divergent gene family. We have used 2 heterologous expression systems to investigate the functional characteristics of a highly conserved subset of Ors between Ae. aegypti and An. gambiae to investigate whether protein homology correlates with odorant-induced activation. We find that these receptors share similar odorant response profiles and that indole, a common and ecologically relevant olfactory cue, elicits strong responses from these homologous receptors. The identification of other highly conserved members of this Or clade from mosquito species of varying phylogenetic relatedness supports a model in which high sensitivity to indole represents an ancient ecological adaptation that has been preserved as a result of its life cycle importance. These results provide an understanding of how similarities and disparities among homologous OR proteins relate to olfactory function, which can lead to greater insights into the design of successful strategies for the control of mosquito-borne diseases.

Activation of MAP kinase signaling pathway in the mussel Mytilus galloprovincialis as biomarker of environmental pollution

Stimulation of MAP kinase signal transduction pathway by various stressful stimuli was investigated in the marine bivalve Mytilus galloprovincialis. Analyses were performed in animals exposed in laboratory to selected pollutants and in mussels collected in winter and summer along the eastern Adriatic coast (Croatia). Effects of oxidative stress, induced by tributyltin, hydrogen peroxide and water soluble fraction of diesel fuel on the activation/phosphorylation of the three Mitogen-Activated Protein Kinases (MAPKs) p38, JNK and ERK using a newly developed ELISA procedure were evaluated. MAP kinase activation was analyzed 1h after exposure of mussels to chemical agents, and after recovery periods of 6 and 24h. Our results clearly indicated that pollutants generated different patterns of induction of the MAPK phosphorylation. Indeed, only pp38 and pJNK were activated with 11, 33 and 100 microg/L TBT, reaching a maximum activation after 6h in seawater following treatment of mussels with 11 microg/L TBT. Treatment with 0.074 and 0.222 mM H2O2 enhanced activation of both p38 and ERK. These two kinases were activated after 1h exposure, followed by a diminution after 6h of recovery in seawater and a reactivation after 24h. The levels of phosphorylated P38 and JNK were increased after mussel exposure with 7.5, 15 and 30% of water soluble fraction of diesel oil. P38 was activated concentration dependently at 1h exposure. Additionally, field study pointed out seasonal differences in MAP kinases activation as mussels collected during summer had a higher enzyme activation state than in winter, as well as sampling site differences which could be correlated to the industrial/tourism activity and environmental stresses (salinity). All the results converge towards MAP kinase signaling pathway being induced by various pollutants in M. galloprovincialis. This signaling cascade should be considered as a possible biomarker of environmental stress and pollution.

Reduced oviposition of Aedes aegypti gravid females in domestic containers with predatory fish

The presence of pathogens or predators in water may alter oviposition behaviour of gravid female Aedes aegypti mosquitoes. We evaluated the oviposition behaviour of A. aegypti in recipients containing larvivorous fish (Betta splendens and Poecilia reticulata). In four breeders, fish specimens were placed in 15 l of dechlorined water. Four control breeders only contained dechlorined water. Breeders with eucatex ovitraps and approximately 100 male and female mosquitoes were placed in wire netting cages. During a period of 7 weeks, eggs on the ovitraps were counted weekly. The median number of eggs laid in recipients with B. splendens (32.5/week) was lower than in those with P. reticulata (200.5/week) and the control group (186.5/week; P < 0.0001). The oviposition activity index (OAI) for P. reticulata did not show any considerable difference between posture in deposits with and without fish (-0005). Deposits with B. splendens showed a lower position than those used as controls (-0627). We conclude that B. splendens can be used to effectively prevent gravid A. aegypti females from laying eggs in large water containers.

Combined sewage overflow enhances oviposition of Culex quinquefasciatus (Diptera: Culicidae) in urban areas

Ecosystem changes caused by anthropogenic activities have modified the environment in ways that at times promote the emergence of vector-borne diseases. Here, we study the effects of combined sewage overflows (CSOs) from urban streams in Atlanta, GA, on oviposition site selection by Culex quinquefasciatus under seminatural field conditions. Counting egg rafts was a reliable indicator of oviposition preferences, and CSO water quality, especially when enriched, was a more attractive oviposition substrate than nonenriched water. Therefore, environmentally sound management of municipal waste water systems has the potential to diminish the risk of Culex-borne diseases in urban areas.

Oviposition responses of Anopheles gambiae s.s. (Diptera: Culicidae) and identification of volatiles from bacteria-containing solutions

In this study, a dual-choice oviposition bioassay was used to screen responses of gravid An. gambiae toward 17 bacterial species, previously isolated from Anopheles gambiae s.l. (Diptera: Culicidae) midguts or oviposition sites. The 10 isolates from oviposition sites have been identified by phylogenetic analyses of their 16S rRNA genes. Eight of the 10 isolates were gram-positive, out of which six belonged to the Bacilli class. Solid phase microextraction and gas chromatography coupled to mass spectrometry (GC-MS) were used to identify the volatiles emitted from the bacterial isolates. Aromatic and aliphatic alcohols, aliphatic ketones, alkylpyrazines, dimethyl oligosulfides, and indole were among the chemical compounds identified from the headspace above bacteria-containing saline. The mosquitoes laid significantly more eggs in six of the bacteria-containing solutions compared with the sterile solution. These six bacteria did not emit any compounds in common that could explain the positive oviposition response. Instead, the bacteria were grouped according to principal component analysis (PCA) based on the relative amounts of volatiles emitted. The PCA-plots facilitated the identification of 13 putative oviposition attractants for An. gambiae mosquitoes.

Transstadial and horizontal transfer of bacteria within a colony of Anopheles gambiae (Diptera: Culicidae) and oviposition response to bacteria-containing water

In a paratransgenic approach, genetically modified bacteria are utilized to kill the parasite in the vector gut. A critical component for paratransgenics against malaria is how transgenic bacteria can be introduced and then kept in a mosquito population. Here, we investigated transstadial and horizontal transfer of bacteria within an Anopheles gambiae mosquito colony with the focus on spiked breeding sites as a possible means of introducing bacteria to mosquitoes. A Pantoea stewartii strain, previously isolated from An. gambiae, marked with a green fluorescent protein (GFP), was introduced to mosquitoes in different life stages. The following life stages or older mosquitoes in the case of adults were screened for bacteria in their guts. In addition to P. stewartii other bacteria were isolated from the guts: these were identified by 16S rRNA sequence analysis and temporal temperature gradient gel electrophoresis (TTGE). Bacteria were transferred from larvae to pupae but not from pupae to adults. The mosquitoes were able to take up bacteria from the water they emerged from and transfer the same bacteria to the water they laid eggs in. Elizabethkingia meningoseptica was more often isolated from adult mosquitoes than P. stewartii. A bioassay was used to examine An. gambiae oviposition responses towards bacteria-containing solutions. The volatiles emitted from the solutions were sampled by headspace-solid phase microextraction (SPME) and identified by gas chromatography and mass spectrometry (GC-MS) analysis. P. stewartii but not E. meningoseptica mediated a positive oviposition response. The volatiles emitted by P. stewartii include indole and 3-methyl-1-butanol, which previously have been shown to affect An. gambiae mosquito behaviour. E. meningoseptica emitted indole but not 3-methyl-1-butanol, when suspended in saline. Taken together, this indicates that it may be possible to create attractive breeding sites for distribution of genetically modified bacteria in the field in a paratransgenic approach against malaria. Further research is needed to determine if the bacteria are also transferred in the same way in nature.

Laboratory and field evaluation of an oviposition trap for Culex quinquefasciatus (Diptera: Culicidae)

An ovitrap (BR-OVT) based on physical and chemical stimuli for attracting gravid Culex quinquefasciatus (Diptera: Culicidae) females was developed and evaluated under laboratory and field conditions. Attractants were assayed using alternative chamber bioassays prior to being used in the BR-OVT oviposition trap. A significant preference of gravid females for sites containing conspecific egg rafts was observed, as a response to the natural oviposition pheromone, as well as for sites treated with the synthetic pheromone erythro-6-acetoxy-5-hexadecanolide. Five- to 20-day old grass infusion was strongly attractive to gravid females for laying eggs. On the other hand, entomopathogenic Bacillus sphaericus (Bs) did not influence the choice of an oviposition site when used in combination with grass infusion and can therefore be used as a larvicide in ovitraps. Results from field trials showed that the BR-OVT with grass infusion and with or without Bs works as a preferred oviposition site for Cx. quinquefasciatus. The BR-OVT was more effective for egg collection when placed indoors and comparison with the number of egg rafts laid in cesspits over 40 days indicates that this very simple ovitrap may be a useful tool for monitoring populations of the most important of the vectors of bancroftian filariasis.

Attraction of gravid anopheles Pseudopunctipennis females to oviposition substrates by Spirogyra majuscula (Zygnematales: Zygnmataceae) algae under laboratory conditions

The attraction of Anopheles pseudopunctipennis gravid females to oviposition substrates containing Spirogyra majuscula algae was investigated under laboratory conditions. Gravid females deposited significantly more eggs in cups containing natural algae in water from breeding sites than in cups containing artificial (nylon rope) life-like algae in water from the corresponding natural breeding site, or in cups containing natural algae in distilled water. Bioassays with Spirogyra majuscula organic extracts indicated that these extracts at concentrations of 0.1%, 0.01%, and 0.001% attracted more oviposition, but concentrations of 1%, 10%, and 100% were repellent. Gas chromatography and mass spectrometry analysis of algae organic extracts revealed a mixture of ethyl acetate and hydrocarbons compounds. These results suggest that the attraction of gravid An. pseudopunctipennis to natural breeding sites containing filamentous algae is probably mediated by organic compounds released by the algae.

Molecular ecological analysis of planktonic bacterial communities in constructed wetlands invaded by Culex (Diptera: Culicidae) mosquitoes

The succession of the planktonic bacterial community during the colonization by Culex (Diptera: Culicidae) mosquitoes of 0.1-ha treatment wetlands was studied using denaturing gradient gel electrophoresis (DGGE) methodology. Relationships between apparent bacterial diversity and ecological factors (water quality, total bacterial counts, and immature mosquito abundance) were determined during a 1-mo flooding period. Analysis of DGGE banding patterns indicated that days postflooding and temporal changes in water quality were the primary and secondary determinants, respectively, of diversity in bacterial communities. Lower levels of diversity were associated with later postflood stages and increases in ammoniacal nitrogen concentration and total bacterial counts. Diversity was therefore most similar for bacteria present on the same sampling date at wetland locations with similar flooding regimes and water quality, suggesting that wastewater input was the driving force shaping bacterial communities. Comparatively small changes in bacterial diversity were connected to natural processes as water flowed through the wetlands. Greater immature mosquito abundance coincided with less diverse communities composed of greater total numbers of bacteria. Five individual DGGE bands were directly associated with fluctuations in mosquito production, and an additional 16 bands were associated with hydrological aspects of the environment during the rise and fall of mosquito populations. A marked decline in mosquito numbers 21 d after inundation may have masked associations of bacterial communities and mosquito recruitment into the sparsely vegetated wetlands. DGGE was an effective tool for the characterization of bacteria in mosquito habitat in our study, and its potential application in mosquito ecology is discussed.

Anopheles gambiae (Diptera: Culicidae) oviposition in response to agarose media and cultured bacterial volatiles

Anopheles gambiae s.s. Giles accepted a range of agarose gels, varying from 0.5 to 8% (wt:vol), for oviposition; laid more eggs on 0.5% agarose gels than on moist filter paper or on drier agarose; and laid equal numbers of eggs on 0.5% agarose gels and distilled water. Larvae hatched on agarose gel substrates and crawled onto the surface of moist agarose gels, but they tended only to burst the egg cap and remain within the egg case on drier gels. A mixture of cultured bacteria, originating from a natural larval habitat of An. gambaiae s.s. in western Kenya, was classified by 16S rDNA sequence analysis, and then this mixture or individual colonies from it was used as odor sources in ovipositional experiments with agarose substrates. Of 61 sequences from a mixed clone sequence library, most (78%) were Pseudomonas strains, whereas the remainder were Stenotrophomonas, Enterobacter, Pantoea, Klebsiella, Acinetobacter, Aeromonas, and Bacillus. Oviposition was significantly reduced when mixtures of bacterial colonies of these strains, or a lawn of colonies of a field isolate of S. maltophilia, was presented. Oviposition was neither reduced nor enhanced when field isolates of Pseudomonas putida or Pseudomonas alcaligenes colonies were presented. These results suggest that gravid An. gambiae females are sensitive to bacterial-derived odors emanating from cultured bacteria from natural larval habitats and that some bacterial odors may be repellent.

Role of bacteria in the oviposition behaviour and larval development of stable flies

Stable flies, Stomoxys calcitrans (L.), are the most important pests of cattle in the United States. However, adequate management strategies for stable flies, especially for pastured cattle, are lacking. Microbial/symbiont-based approaches offer novel venues for management of insect pests and/or vector-borne human and animal pathogens. Unfortunately, the fundamental knowledge of stable fly-microbial associations and their effect on stable fly biology is lacking. In this study, stable flies laid greater numbers of eggs on a substrate with an active microbial community (> 95% of total eggs oviposited) than on a sterilized substrate. In addition, stable fly larvae could not develop in a sterilized natural or artificial substrate/medium. Bacteria were isolated and identified from a natural stable fly oviposition/developmental habitat and their individual effect on stable fly oviposition response and larval development was evaluated in laboratory bioassays. Of nine bacterial strains evaluated in the oviposition bioassays, Citrobacter freundii stimulated oviposition to the greatest extent. C. freundii also sustained stable fly development, but to a lesser degree than Serratia fanticola. Serratia marcescens and Aeromonas spp. neither stimulated oviposition nor supported stable fly development. These results demonstrate a stable fly bacterial symbiosis; stable fly larval development depends on a live microbial community in the natural habitat, and stable fly females are capable of selecting an oviposition site based on the microbially derived stimuli that indicate the suitability of the substrate for larval development. This study shows a promising starting point for exploiting stable fly-bacterial associations for development of novel approaches for stable fly management.

Volatile substances from larval habitats mediate species-specific oviposition in Anopheles mosquitoes

Oviposition site selection has been recognized as critical both for the survival and population dynamics of mosquitoes. Volatile substances released from larval habitats have been implicated as potential olfactory cues mediating oviposition. In our continuing studies of cues involved in oviposition site selection, we collected material from the larval habitats of Anopheles albimanus Wiedemann and Anopheles vestitipennis Dyar & Knab, i.e., cyanobacterial mats and Typha domingensis Pers. litter, respectively. The volatile compounds were extracted by freeze-drying the material and trapping the volatilized material on a -55 degrees C titanium condenser. For oviposition trials conducted with wild-caught females, the tested volatile materials were pipetted onto filters floating on the surface of distilled water in Teflon beakers that were placed within oviposition cages. For both species, volatile materials in low concentrations increased oviposition, assessed as egg density, whereas there was a shift to reduced oviposition at higher concentrations. Volatile effect was strongly habitat/species-specific as shown by reciprocal treatment tests.

The hidden lifestyles of Bacillus cereus and relatives

Bacillus cereus sensu lato, the species group comprising Bacillus anthracis, Bacillus thuringiensis and B. cereus (sensu stricto), has previously been scrutinized regarding interspecies genetic correlation and pathogenic characteristics. So far, little attention has been paid to analysing the biological and ecological properties of the three species in their natural environments. In this review, we describe the B. cereus sensu lato living in a world on its own; all B. cereus sensu lato can grow saprophytically under nutrient-rich conditions, which are only occasionally found in the environment, except where nutrients are actively collected. As such, members of the B. cereus group have recently been discovered as common inhabitants of the invertebrate gut. We speculate that all members disclose symbiotic relationships with appropriate invertebrate hosts and only occasionally enter a pathogenic life cycle in which the individual species infects suitable hosts and multiplies almost unrestrained.