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Study of mosquito attractants for photo catalytic mosquito trap


Abstract and Figures

Photo catalytic mosquito trap is made of TiO2-Activated Carbon (AC) with a certain composition of AC. Research concerns on the heat spectrum which is produced by combination process of existing CO2 and humid air. The purpose of performance testing is to observe capability of this device in trapping mosquitoes related to the air temperature profile for heat spectrum is play important role for attracting mosquitoes. Result shows photo catalytic mosquito trap is more effective than devices which only consist of UV light or stream of CO2 and the humid air. A number of mosquitoes trapped by the photo catalyst coated panel configuration and UV lamps were lit proved far more effective because the heat production from recombination process. A little difference in temperature can be detected by mosquito. Keywords: Photo Catalytic, Mosquito, Recombination.
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International Journal of Engineering & Technology, 3 (1) (2014) 14-19
©Science Publishing Corporation
doi: 10.14419/ijet.v3i1.1478
Research Paper
Study of mosquito attractants for photo
catalytic mosquito trap
Dewi Tristantini*, Slamet, Angela Jessica Stephanie
Chemical Engineering Department, Engineering Faculty, University of Indonesia Kampus Baru
*Corresponding author E-mail:
Copyright © 2014 Dewi Tristantini et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original work is properly cited.
Photo catalytic mosquito trap is made of TiO2-Activated Carbon (AC) with a certain composition of AC. Research
concerns on the heat spectrum which is produced by combination process of existing CO2 and humid air. The purpose
of performance testing is to observe capability of this device in trapping mosquitoes related to the air temperature
profile for heat spectrum is play important role for attracting mosquitoes. Result shows photo catalytic mosquito trap is
more effective than devices which only consist of UV light or stream of CO2 and the humid air. A number of
mosquitoes trapped by the photo catalyst coated panel configuration and UV lamps were lit proved far more effective
because the heat production from recombination process. A little difference in temperature can be detected by mosquito.
Keywords: Photo Catalytic, Mosquito, Recombination.
1. Introduction
In a tropical country like Indonesia, the growth of mosquitoes is extremely rapid. Mosquitoes can transmit in various
types of diseases to human. Global warming increases surrounding air temperature which is also suitable for
mosquitoes’ propagation. Currently, the number of mosquitoes has reached 5 times the human population [1].
Anti-mosquito products are available in the market. Although proven effective to kill and drive out mosquitoes, it is
dangerous for human health. Mosquito spray, gas, and electric have active ingredients such as organophospate group
banned that are carcinogenic.
A new environmentally friendly solution can be used as mosquito trap is a photo catalytic process, utilizes energy
photons and TiO2 as potentially catalyst. Photo catalytic process is able to degrade various pollutants of air space and
produce CO2 and water vapor from the process and heat spectrum from recombination process. UV light (as source of
photon energy) also attracts mosquitoes. These reaction scan be used as attractant for mosquito come into this mosquito
trap. In this trap, deceived mosquitoes will be attracted to become closer, trapped, and death of dehydration.
The photo catalytic device based mosquito traps that have been certified international patent no. Domestic PCT/KR/01-
00427 and Korean Patent No. 43,847 in 2001. Although the devices available mosquito traps have been proved
effective to trap and kill mosquitoes, these devices have various shortcomings such as relatively expensive price,
availability must be imported from abroad, and especially the claim that these mosquito trap devices can degrade the air
pollutants that need to be questioned again because form design device that made it less effective. One technique that
allows the increase rate of indoor air pollutants degradation in order to get CO2 and water vapor as mosquito attractants
is to use adsorbent (activated carbon) as a buffer photo catalyst TiO2[2]. Addition of activated carbon (15% composition
weight) is the most optimum result and effective in catching mosquitoes. It is close with 13% composition weight of
activated carbon using for pollutant reduction. [3]
Comparison study for commercial mosquito trap shows that Mosquito Magnet Pro and Mosquito Magnet Liberty
mosquito trap and Bug Eater are better. It was assumed that CO2 from those devices more attractive to mosquitoes [4].
Heat spectrum is also play important role for attracting mosquitoes. Temperature will significantly affect the activity of
mosquitoes. Higher temperature showed that mosquitoes are more active and more attractive for mosquitoes to come
closer. [5].
International Journal of Engineering & Technology
In this study, the mechanism of mosquitoes attracting is based on the hypothesis that there are various mosquito
attractant such as CO2, water vapor and heat of the spectrum will be studied. By knowing the most dominant mosquito
attractor factor then the effectiveness of the tool in attracting mosquitoes can be improved.
2. Experimental
2.1. Device design
Figure 1 shows the construction of mosquito trap device for a configuration based on the various considerations
mentioned previously. It can be seen there are 2 lamps UV-A arranged on the upper side.
Fig. 1: Photo catalytic mosquito trap
In addition, the placement of the fan blade is in the middle of the tube for focus on trapping mosquitoes. Around the fan
blade, installed a buffer that can serve as a panel of TiO2. At the bottom of the screen there is a device that serves as a
place for air discharge and mosquito net barrier to exit. Thermometers are placed on four positions so it can be . T1 is
temperature in panel aluminum, T2 is temperature in the upper side of air lattice, T3 is temperature in the lower side of
air lattice and T4 is temperature outside mosquito trap which 3 cm in front of air lattice.
2.2. Photo catalyst adsorbent coating
There are two considerations for selection of coating methods, (1) method of making an attached film to the substrate
without any transparency effect, (2) type of buffer panels made of aluminum. In this study, we choose the film
preparation using direct TiO2 powder spray coating methods. Steps for composite coating are as follows:
First, treatment of activated carbon (AC) by washing and then drying it in furnace at a temperature of 250°C for 1 hour
and followed by grinding them into a fine powder of AC. The AC powder then sized for 0.125mm sieve
Second, the suspension formation of TiO2-AC by dissolving TiO2 powder mixture into 100 mL of demineralized water
and sonicating for 10 minutes. AC added to 1 mL of TEOS (tetraethyl orthosilicate) solution into the former solution
then sonicating for 20 minutes more. The clean panel covered with aceton and TiO2 suspension sprayed into the
aluminium area panels using a spray gun and dried panel with a hair dryer first. Repeating the two later steps 5 times
until a uniform layer of aluminum on panel formed. The last, drying the coated panel by using a programmable oven at
a temperature of 150°C for 1 hour.
2.3. Device performance test
To know the performance for each trap used in experiment, blank test is done. For first day, trap A tested by using panel
with composite and after that following by CO2 and water vapor and trap B only tested by using panel with composite.
The next day, trap A is tested by using panel with composite and trap B by using panel with composite and flowed by
CO2 and water vapor.
2.3.1. Role of CO2 and water vapor as mosquito’s attractant
To test the role CO2 and water vapor, CO2 and water vapor is flowed into mosquito trap with aluminum panel which is
non-coating and without using UV lamp.
This test is conducted for 12 hours (7 pm until 7 am). Testing is done using variation of CO2 flow (400 cc/minutes, 450
cc/minutes and 500 cc/minutes). One device uses the flow of CO2 and water vapor and another without them.
2.3.2. Role of heat spectrum as mosquito’s attractant
To test the role of heat spectrum, thermocouple K that is connected to data acquisition Adamtech is used for detecting
temperature at four positions around the mosquito trap.
The test is conducted for 4 hours (240 minutes) where UV and fan are turned on. Variable in this test is the treatment
for the aluminum panel. There are two panels, panel with composite and panel without composite. In result, the profile
of temperature for each treatment can be performed.
2.3.3. Role of photo catalyst
Testing the role of photo catalyst is intended to test the capabilities of photo catalyst to attract mosquitoes. This test is
conducted for 12 hours (7 pm until 7 am). Testing is done to compare the photo catalytic trap with mosquito trap with
CO2 flowed at rate 450 cc/minutes and water vapor and also with mosquito trap with only UV as its attractant.
3. Results and discussion
Two devices are used in this experiment. In order to know the ability of each trap, the blank test was done with the
results as shown in Figure 2.
Fig. 2: The result of blank test
It can be seen from Figure 2, the performance for those devices in trapping mosquito are similar for day 1 and day 2.
This blank test is to ensure there is no intrusion or problems with part of each trap. From this blank test, CO2, water
vapor and photocatalyst gives positive impact in attracting mosquito rather than photocatalyst alone.
3.1. Role of CO2 and water vapor as mosquito attractant
Tests are conducted to see the role of CO2 in attract mosquitoes to come and become trapped in the device and die
because of dehydration from a straw stuck in a constant fan. A test conducted by state UV lamp off and the fan is on.
Testing was done in laboratory warehouse with bright weather and rainy weather.
The test results are shown in Figure 3 and Figure 4, are the mosquito trap with CO2 and water vapor will attract and trap
more mosquito than the mosquito trap without CO2 and water vapor. It is because CO2 can be detected by mosquitoes
from 18-36 meter and humidity from water vapor will also attract mosquitoes [6].
3.2. Role of heat spectrum as mosquito’s attractant
This test is intended to see the role heat spectrum as mosquito attractant. Testing is done with state of UV light and fan
on. The treatment of panel were varied A with and without composite. Testing is done in 2 days which is cloudy at the
same place. Because the temperature from each day is not same, we use T/T0 for analysis to compare data from one day
to another day.
International Journal of Engineering & Technology
Fig. 3: The results of bright weather
Fig. 4: The results of rainy weather
Fig. 5: Temperature profile for panel without composite
Fig. 6: Temperature profile for panel with composite
Tests are shown in Figure 5 and Figure 6, weather really influence the recorded temperature. As seen in those figures,
the temperature can be higher or lower minute by minute. In overall, the temperature for will be increase because the
UV lamp will become hotter after a period time of testing. On the other hand, panel with composite will become hotter
also because of heat that probably comes from the recombination process [7].
The role of photo catalyst-adsorbent at panel can be seen by comparing the profile of T1 which is temperature at panel.
Fig. 7: Temperature profile at panel
Based on Figure 7, the increasing temperature on panel with composite is relatively faster than increasing temperature
on panel without it. This clearly shows that photocatalyst activated by photon energy of UV light will produce heat
through recombination process which is dominating in photocatalytic process [7].
3.3. Role of photo catalyst
This test is intended to see the role of photocatalyst on this device.
Based on Figure 8, the photocatalyt process will attract mosquitoes because of the heat spectrum as the result of
recombination process. Mosquitoes will be attracted to testing location because it was detected at their receptor. For
closer attractants, mosquito will be attracted more with certain wavelength of heat spectrum and UV light [8]. The
photocatalytic process will clearly more effective in catching mosquitoes which can be analyzed through photocatalytic
Fig. 8: Effect of photo catalyst
The light of UV-A (with a wavelength of 365 nm) will enable providing the energy required for exciting electrons from
the valence band into the conduction band of TiO2. Electrons (e-) in the valence band will move into the conduction
band, leaving positive holes (abbreviated as h+) in the valence band. This event is called excitation. However, most
couples of e- and h+ will recombine again, either on the surface of the particle or in the bulk phase, while producing
heat energy equivalent to human body heat radiation. The recombination events dominate in the photo-catalytic
mechanism [7]. Mosquitoes are coming into this device can be caused by heat energy generated by the recombination
process. Electrons in the valence band that managed to move to the conduction band will leave a hole in the conduction
band. Part of the hole formed will react with water vapor in the air to form hydroxyl radical (•OH), while the electrons
will react with oxygen molecules to form radical anion superoxide (•O2-) [9]. If there is an organic species in a room
where the instrument is placed radicals are highly reactive forms will cooperate in a completely oxidize the organic
species [9]. The photo-catalytic radicals are able to degrade various air pollutants in the living room into carbon dioxide
and water vapor [10]. Product carbon dioxide produced from the photo-catalytic process will be an attraction for
mosquitoes to get closer to the device [12]. Both heat generated by recombination events as well as carbon dioxide are
produced if there is an organic compound will be degraded mosquito attractants to approach this device.
Testing result for air around photo catalytic mosquito trap indicates that there is no CO2 and water vapor detected. It is
likely that the indoor air pollutant is in very small concentration or even there is not any indoor air pollution thus there
is no CO2 and water vapor produced.
At times during the 12-hour test also attracted mosquitoes into a prototype device that is not coated photocatalyst and its
UV lamp still on. Attraction of mosquitoes to the prototype device caused by the heat generated by UV lamps was lit so
long after mosquitoes taken, and fall into the trap. UV light can also attract mosquito especially Anopheles stephensi.
[12]. A number of mosquitoes trapped by the photo catalyst coated panel configuration and UV lamps were lit proved
far more effective because the heat production from recombination process. A little difference in temperature can be
detected by mosquito. Thermo receptor sensitivity in the mosquito can detect in accurateness of 0.2oC, thus the
difference of 1-2oC can give significant impact in attracting mosquitoes [13], [14].
4. Conclusion
Based on the results of research and discussions that have been described previously, obtained some conclusions,
CO2 and water vapor give positive impact as mosquito attractant.
UV light also can attract mosquito into the device.
Heat spectrum which is produce by recombination process plays significant role than CO2 and water vapor or UV
light in attracting mosquitoes.
If the device put in room contain with indoor air pollutant, the effectivity for this device will increase by the
production of CO2 and water vapor.
The present study was supported by “Penelitian Unggulan Perguruan Tinggi (Desentralisasi Dikti)” the Directorate of
Higher Education, Department of Education and Culture Republic of Indonesia.
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... Host-attractant baited traps and targets are some of the promising environmentally friendly technologies currently being considered for mosquito control since the beginning of the last decade [15,28,29]. Volatile attractive host odor has been recognized to play an important role in guiding malaria vectors to the human host and preferred feeding site(s) [15,16,24,[30][31][32][33][34]. ...
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Background Several human-produced volatiles have been reported to mediate the host-seeking process under laboratory conditions, yet no effective lure or repellent has been developed for field application. Previously, we found a gradation of the attractiveness of foot odors of different malaria free individuals to Anopheles gambiae sensu stricto Giles. In this study, foot odor of the individual with the most attractive ‘smelly’ feet to the An . gambiae was collected, analyzed and attractive blend components identified. Methods The foot odor of the individual with the most attractive ‘smelly’ feet to the An . gambiae was trapped on Porapak Q and analyzed by gas chromatography-linked mass spectrometry (GC-MS). Specific constituents perceived by the insect olfactory system were then identified by GC-linked to electro-antennography detector (GC-EAD) and characterized by GC-MS. The contribution of each constituent to the behavioral response of An . gambiae was assessed through subtractive assays under semi-field conditions in a screen-house using Counter Flow Geometry (CFG traps) baited with (i) the blend of all the EAD-active and (ii) other blends containing all components with exclusion of one component at a time. The number of mosquitoes trapped in the baited CFG traps were compared with those in the control traps. Results Eleven major and minor constituents: 2 carboxylic acids, six aldehydes, two ketones and one phenolic compound, were confirmed to be EAD-active. The contribution of each constituent to the behavioral response of An . gambiae was assessed through subtractive assays under semi- field conditions. Exclusion/ subtraction of one of the following compounds: i- butyric acid, i- valeric acid, n -octanal, n -nonanal, n -decanal, n -dodecanal, undecanal or n -tridecanal, from each blend led to reduction in the attractiveness of all the resulting blends, suggesting that all of them are critical/important for the attractiveness of the foot odor to An . gambiae mosquitoes. However, exclusion/subtraction of 4-ethoxyacetophenone, 4-ethylacetophenone and/or 2-methylphenol, led to significant enhancements in the attractiveness of the resulting blends, suggesting that each of these compounds had repellent effect on An . gambiae ss . Undecanal exhibited kairomonal activity at low natural concentrations under semi-field conditions but repellent activity at high unnatural conditions in the laboratory. Furthermore, the comparison of the mean mosquito catches in traps baited with the nine-component blend without 4-ethoxyacetophenone, 4-ethylacetophenone and the complete foot odor collection revealed that the former is significantly more attractive and confirmed the repellent effect of the two carbonyl compounds at low natural concentration levels. Conclusion These results suggest that differential attractiveness of An . gambiae to human feet is due to qualitative and/or qualitative differences in the chemical compositions of the foot odors from individual human beings and relative proportions of the two chemical signatures (attractants versus repellents) as observed from the ratios of the bioactive components in the foot odors of the most attractive and least attractive individuals. Chemical signature means the ensemble of the compounds released by the organism in a specific physiological state. The chemical signature is emitter-dependent, but does not depend on receiver response. Thus, there is only one chemical signature for one individual or species that may eventually include inactive, attractive and repellent components for another organism. The nine-component attractive blend has a potential as an effective field bait for trapping of malaria vectors in human dwellings.
... This action would reduce the water vapor as mosquito attractant. 23 Another study reported that coconut oil-derived fatty acid also showed even better repellent activity than DEET. 24 In contrast, another study reported that soybean oil itself had no repellent activity but only supported other repellent's effectivity. ...
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Latar Belakang: Penelitian mengenai sintesis Atraktan Asam Laktat-Asam Asetat-Amoniak untuk Pengendali Populasi Nyamuk Aedes sp telah dilakukan. Penelitian ini bersifat eksperimental.Tujuan: Penelitian ini bertujuan untuk mengetahui efektivitas Model Atraktan Asam Laktat-Asam Asetat-Amoniak. Pengujian hasil penelitian ini mengambil lokasi di Daerah Kecamatan Mungkid, Magelang, Jawa Tengah sebagai tempat dimana Aedes albopictus terdapat banyak.Metode: Metode sampling penelitian yang dilakukan bersifat random. Hasil: Hasil dari penelitian ini telah membuktikan bahwa dengan komposisi 85% asam Laktat, 12,5 % asam Asetat dan 2,5 % amonia, mempunyai kemampuan sebagai atraktan nyamuk Aedes sp. Hasil penelitian ini dikaji dengan standar Pedoman Pengumpulan Data Vektor (Nyamuk) di Lapangan : Riset Khusus Vektor dan Reservoir Penyakit di Indonesia yang diterbitkan oleh Balai Besar Penelitian dan Pengembangan Vektor dan Reservoir Penyakit Badan Penelitian dan Pengembangan Kesehatan Kementerian Kesehatan R.I. Tahun 2017.Kesimpulan: bahan aktif yang diuji efektif dijadikan atraktan. Hasil penelitian ini sebagai suatu solusi dalam mengendalikan populasi nyamuk Aedes sp. di tempat lain.
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Malaria is one of the most serious human diseases, affecting between 300 and 600 million people per year and killing, on average, two children per minute. In tropical Africa the mosquito Anopheles gambiae Giles sensu stricto is responsible for much of the transmission of malaria parasites between humans. This mosquito species preferably feeds on human blood, rests inside human houses and breeds close to human dwellings, making it an effective malaria vector. The major cues guiding Anopheles gambiae females to their human hosts are volatiles emanating from the human body. The main aim of the present thesis was to investigate the chemical components in human emanations that play a role in the host-seeking behaviour of this mosquito species and how these human odours are perceived by the olfactory system of the mosquito. The knowledge obtained can be applied in developing odour-baited traps that can be used to protect humans from being bitten by mosquitoes or to decrease the chance of being bitten by mosquitoes and to provide an alternative for the traditional but questionable "human landing" method in the investigation of mosquito population size. Glass beads to which skin emanations from human hands had been transferred elicited a level of attraction similar to a human hand ( Chapter 2 ). The attractiveness of these handled glass beads faded away four hours after transfer onto the beads. The headspace of handled glass beads elicited a dose-dependent EAG response. Glass beads provided a suitable neutral substrate for the transfer of human odour to enable the investigation of behavioural and electrophysiological activities of An. gambiae exposed to these odours and to allow chemical analysis of the human skin emanations by gas-chromatography-mass spectrometry performed in a twin-project. To study the chemical basis for the inter-individual differences in human attractiveness to mosquitoes , emanations from 27 human individuals, collected on glass beads, were tested against ammonia in a dual-choice olfactometer to establish the degree of attractiveness to An. gambiae ( Chapter 3 ). There were clear differences in the trap entry response as well as in the attractiveness relative to that of ammonia between the skin emanations of different volunteers. Consistency of the differences was observed when emanations of the three most and the three least attractive volunteers were tested pair-wise. Emanations from males elicited a higher trap entry response than those from females. Odours of younger volunteers significantly raised the trap entry response and were preferred over odours from older volunteers. Electroantennogram responses to skin emanations from volunteers with different behavioural attractiveness were not in all cases positively related to the behavioural response level, suggesting the involvement of repellent components. Stockings worn by humans were previously shown to be highly attractive to females of An. gambiae . The headspace of nylon stockings was collected and analysed with gas chromatography coupled on-line to electroantennography (EAG). EAG responses were detected consistently at 23 retention times, and 14 compounds that elicited such EAG responses were tentatively identified. These compounds, however, were not of typically human origin ( Chapter 4 ). Ammonia, L-lactic acid and a mixture of carboxylic acids were previously found attractive to An. gambiae. These compounds are all present in human skin odours, therefore a mixture of these components was studied in a dual-choice olfactometer ( Chapter 5 ). Ammonia was an attractant on itself, whereas lactic acid alone was not attractive. Carboxylic acids, offered as a mixture of 12 compounds, were repellent at the concentration tested. The addition of ammonia to the carboxylic acid mixture overruled the repellent effect of the latter. Combining ammonia with either lactic acid or the carboxylic acid mixture did not enhance the attractiveness of ammonia alone. However, a synergistic effect was found when ammonia, lactic acid and the carboxylic acids were applied as a blend. Human odour compounds that elicited electrophysiological or behavioural responses were tested in combination with ammonia + L-lactic acid against ammonia alone ( Chapter 6 ). The results showed that C3-C8 and C14 carboxylic acids augmented the attractiveness of ammonia + lactic acid at certain concentrations, whereas alcohols , ketones , 4-ethylphenol and indole only reduced the attractiveness at the concentrations tested. For some compounds, no effect was found at any of the concentrations tested. Based on the behavioural and electrophysiological findings, a field study in The Gambia ( West Africa ) was carried out to investigate the efficiency of mosquito traps baited with synthetic odour blends or human odour ( Chapter 7 ). This study showed that odours released from counterflow geometry (CFG) traps baited with up to nine compounds that were mixed during release were in many cases more attractive than odours from a tent occupied by a human. Carbon dioxide substantially increased the catch of the CFG traps for all mosquito species. CFG traps baited with the mixture of ammonia + lactic acid + 3-methyl butanoic acid + CO <sub>2</sub> resulted in the highest catches for most mosquito groups; the mixture is considered to be a promising candidate odour blend in the control of nuisance mosquitoes. Experiments with traps indoors showed that one odour mixture, consisting of ammonia + lactic acid + CO <sub>2</sub> + geranyl acetone + indole + 4-ethyl phenol was more attractive for An. gambiae than the control odour; this mixture holds promise for further experiments under conditions of higher An. gambiae abundance and for implementation in vector control programs. Using a single sensillum recording method, an electrophysiological study on the olfactory neuron responses of female An. gambiae mosquitoes was undertaken ( Chapter 8 ). Six functional types of sensilla trichodea and five functional types of sensilla basiconica (grooved peg sensilla) were identified. "Generalist" ORNs that are tuned to a broad range of odours were found in sensilla trichodea subtype E, whereas "moderate specialist" ORNs that are tuned to a narrow range of odours were found in subtype C and grooved peg sensilla, with two "extreme specialist" ORNs tuned to only one odour. There was overlap in response spectra between sensilla trichodea E and C or grooved peg sensilla, but no overlap was found between sensilla trichodea C and grooved peg sensilla except that both responded to ammonia. Neurons associated with the same sensillum tended to respond to similar odour stimuli but with different sensitivities. Neurons in grooved peg sensilla were tuned to more polar compounds including the important behavioural attractant ammonia and its synergist lactic acid, responses to which were only found in grooved peg sensilla. Phenols were among the most effective stimulants for several neuron types belonging to different functional classes. Across-fibre patterning is the most plausible coding principle operating in the olfactory system of this mosquito species. After a blood meal, female mosquitoes minimise host seeking activity and rest during egg maturation. To investigate whether the sensitivity of olfactory neurons changed after a blood meal and whether these changes correlate with the observed behavioural change, we compared the responses of ORNs in sensilla trichodea and grooved peg sensilla 2 - 24 h post blood meal with that of mosquitoes that had not fed on blood ( Chapter 9 ). Three instead of two functional types of sensilla trichodea E were found following a blood meal. A functional type that had not been detected in mosquitoes deprived of blood was found repeatedly. The most responsive neuron of the "new" functional type of sensillum showed a high sensitivity to indole. This neuron was also highly responsive to C6-9 carboxylic acids and moderately responsive to the human-specific odour compounds 7-octenoic acid and 3-methyl-2-hexenoic acid. These results indicate that changes in sensitivity and response profile of ORNs as a result of a blood meal are involved in modulating behaviour of An. gambiae females. The main conclusions from this thesis can be summarised as follows. This thesis provides additional evidence that chemical cues play a substantial role in the host attraction of An. gambiae (Chapter 2) and that skin emanations alone contribute significantly to inter-individual differences in attractiveness of humans to mosquitoes (Chapter3). The GC-EAG method can be used in the detection of kairomones used by An. gambiae , but a suitable substrate for collecting odours is essential (Chapter 4). Synergism was demonstrated to operate between ammonia, lactic acid and a mixture of carboxylic acids in attracting females of An. gambiae (Chapter 5) and olfactometric studies demonstrated the dose-dependent effects of human odour components to An. gambiae in addition to ammonia and lactic acid (Chapter 6). The results of our field study provided evidence that mosquito traps baited with synthetic mixtures were superior to those baited with a human being, suggesting great potential of these traps in future malaria control programs (Chapter 7). Based on the response to several compounds, olfactory receptor neurones were classified into functional groups, providing fundamental information for future studies of these neurons (Chapter 8). Qualitative and quantitative changes were found in olfactory neuron responsiveness before and after a blood meal, suggesting the involvement of the peripheral nervous system in the modulation of mosquito behaviour observed in different physiological stages (Chapter 9).
The use of stereolithography is well suited for the fabrication of a monolithic photocatalyst for cleaning of air contaminated by volatile organic compounds (VOCs). In this paper we present the influence of the geometry of the monolith on the reactor's efficiency. Our aim is to develop a model that describes the basic phenomena, which are involved, i.e., light absorption, hydrodynamic and transfer processes and the reaction kinetics. Three different geometries of the monolith reactor have been tested: mixer (M), crossed channels (C), and star geometry (S). It appears that the geometry has practically no influence on the external mass transfer rate but has a great influence on the kinetics of photocatalysis. The model will be used to predict and optimize the photocatalytic behaviour and to scale up the results to an industrial reactor.
PREVIOUS work has indicated that attractive factors other than carbon dioxide are present in the vapour from mammalian blood1 and body exudations2. A distillate obtained from mammalian blood proved highly attractive to Culex pipiens3. It has been recently reported that a mixture of nine biological acids and bases was attractive to C. pipiens and Anopheles maculipennis at concentrations down to 0.05 per cent, although none of the compounds was attractive when tested individually4.
Well-aligned rutlie and anatase TiO2 nanorods as well as anatase TiO2 nanowalls have been synthesized using a template- and catalyst-free metalorganic chemical vapor deposition (MOCVD) method. Structural analyses indicate that single-crystalline rutile and anatase TiO2 nanorods were formed at 630 °C and 560 °C, respectively, while anatase TiO2 nanowalls composed of well-aligned nanorods were formed at 535 °C. Optical characterizations of these TiO2 nanostructures show that the band gap energies for indirect transistion of the rutile TiO2 nanorods and anatase TiO2 nanorods as well as nanowalls are at 3.0 and 3.2 eV, respectively.
18. Reasons are given for considering that the measure of humidity which determines the behaviour of the mosquito is relative humidity and not saturation deficiency, even though the latter is the important one in the water relations of insects.
1. A pair of thermoreceptor units was identified in the sensilla coeloconica at the tip of the antennae on the mosquito,Aedes aegypti. 2. One thermoreceptor was warm-sensitive and responded with a phasic-tonic increase in spike frequency to sudden increases in temperature. The second thermoreceptor was coldsensitive, responding with a phasic-tonic increase in spike activity to sudden decreases in temperature. 3. The mean tonic spike activity of both the cold and warm receptors increased with increasing temperature to a peak of 30 imp/sec at 26 C for the cold receptor and 35 imp/sec at 28.5 C for the warm receptor. The tonic activity declined as the temperature was increased further. The maximum phasic sensitivity was observed with small temperature changes ( T = 0.2C). This was 136 imp/sec/C temperature drop in the cold receptor and 130 imp/ sec/ C rise in the warm receptor. 4. The importance of temperature in the host-seeking and attack behavior of the mosquito is discussed.
Previously we identified that residence time and water vapor are the vital parameters that affect the photodegradation of indoor air pollutants at parts-per-billion (ppb) levels using TiO2. The presence of water vapor competes with pollutants for adsorption sites on TiO2 thus reducing the pollutant removal rate. By immobilizing TiO2 on activated carbon (AC), a satisfactory pollutant removal rate is achieved even at high water vapor levels. This study further examines the effect of TiO2 immobilized on AC by co-injecting binary pollutants simultaneously since the presence of other pollutants might have an inhibition effect on the photocatalytic activity under different humidity levels. 200 parts-per-billion NO, 20 ppb BTEX and 200 ppb SO2 were co-injected under different residence time and humidity levels to investigate their mutual effect on TiO2 and TiO2 immobilized on AC. Results showed that no significant pollutant removal difference was observed between TiO2 and TiO2 immobilized on AC at longer residence time. The presence of BTEX only reduced NO conversion by 5%. At evaluated humidity levels, however, a significant different pollutant removal rate was observed. The presence of BTEX reduced NO conversion by more than 10%. The use of TiO2 on AC, reduced both the competition effect of the pollutant and water vapor on TiO2. The inhibition effect of BTEX and SO2 on NO conversion was significantly reduced when TiO2 immobilized on AC compared to TiO2 only. The by-product, NO2, from the photodegradation of NO, was also reduced despite the presence of SO2 and BTEX under high humidity level.
In the present work, the effect of mixing TiO2 with different portions of activated carbon (AC) has been studied. Transmission electron microscopy (TEM), scanning electron micrograph (SEM), laser scattering, FTIR and UV spectrophotometric analysis have shown changes of some of the TiO2 physico-chemical characteristics in catalysts containing an AC concentration lower than 15% in weight. Changes in the catalyst colour, the vibration bands of the hydroxylic groups from FTIR studies and the UV absorption spectrum have been observed. It seems that these changes correspond with TiO2 acid–base changes. SEM and TEM studies show a perfect TiO2 particles distribution on the AC surface in catalysts with lower AC contents, that also yields a homogeneous particle size distribution. One of the most interesting features of the resulting catalysts is their fast decantability in comparison with that of TiO2. This way one of the most important drawbacks of photocatalysis, the catalyst separation from the solution, may be overcome.The present study shows that the AC not only exerts a synergistic effect when is combined with TiO2 as some authors suggest, but it also modifies the catalyst characteristics.
A silver ion doped TiO2 based photocatalyst, with improved destruction of airborne microbes, has been developed. The performance of the silver ion doped photocatalyst is demonstrated using a catalyst coated filter in a recirculating air experimental facility. Bacillus cereus, Staphylococcus aureus, Escherichia coli, Aspergillus niger, and MS2 Bacteriophage have been used as indexes to demonstrate the high disinfection efficiency of the enhanced photocatalysis process. The microbial destruction performance of the enhanced photocatalyst is found to be an order of magnitude higher than that of a conventional TiO2 photocatalyst. The process of enhanced photocatalysis can thus be used effectively against high concentrations of airborne microorganisms, making it an attractive option as a defense against bio-terrorism.