A research for an eco-friendly mosquito control by using a new mosquito trap (Mos-hole trap) in a cowshed in Yeoju of Korea

Abstract

We performed this study to find out if we could control mosquitoes in a cowshed by using CO₂-baited mosquito traps. We used eco-friendly Mos-hole traps that were developed for mosquito control in human living areas and we also evaluated the traps' efficacy, if the traps would be effective in controlling mosquitoes in a cowshed. The study was performed for 54 days (from 18 May to 10 July 2012). During the first nine turns (from 18 May to 18 June), we used 12 mosquito traps, which were baited with low CO₂ emission (35–100 ml/minute) by burning and combusting liquid naphtha. In the next phase (10 to 13 turns; 21 June to 4 July), we kept the same low CO₂ emission in six traps but increased the CO₂ concentration (500 ml/minute) in the other six traps. In the 14th turn (July 10), all 12 mosquito traps were used with higher CO₂ concentration, using compressed cylinders of CO₂. Mosquitoes were collected at each turn and the total trapped female mosquitoes during the study period were 31,715 individuals, and we identified 6 genera and 16 species. The predominant species was Aedes vexans nipponii (63.838%). We found that 5.2 times more mosquitoes were caught at higher emission rates of CO_2. Finally, our study partly revealed that higher emission of CO₂ might be a reliable substitute for proper control of the adult female mosquitoes and we absolutely need to develop a more efficient mosquito trap for cowshed areas.

Keywords:

• cowshed
• CO₂ emission
• female mosquito control
• Mos-hole trap

Introduction

During the last 10 decades, the earth's average temperature has risen by about 0.7°C (Revich et al. 2012). Most of the natural scientists in the world believe that global warming is caused by anthropogenic activities which resulted in the increased concentrations of greenhouse gases, such as carbon dioxide, methane, nitrous oxide and ozone (Karl & Trenberth 2003). This increased greenhouse gas concentrations have warmed up the earth's water and atmosphere temperature. Such increases of water and air temperature also affect insects' life cycles. For example, the increased water temperature would enhance the growth of mosquito larvae and the female mosquitoes are able to produce more offspring. The female mosquitoes would be able to digest blood meal quickly because of increased air temperature and so they suck blood more frequently. From those results it is evident that the mosquitoes would be faster disease vectors in geographic range levels (Githeko et al. 2000; Reiter 2001).

The World Health Organization (2003) reported that 30 new diseases have recently emerged in the world (Epstein et al. 1998). Mosquitoes have vectored worldwide resurgence and redistribution of diseases such as malaria and dengue fever (Epstein et al. 1998; Gubler & Kuno 1998). Especially, Japanese encephalitis (JE) has had a higher incidence in several countries including Japan, Philippines, Indonesia, India and South Korea. Mosquitoes have been the nuisance pests, remaining close to human living areas and affecting human life for a long time (Tellez-Rebollar 2005; Hubalek 2007). More than 3 billion people in 107 countries live under the threat of malaria transmission. Because of mosquitoes, 300–500 million people get infected with Malaria annually, and every year over 1 million people die of malaria. Unfortunately, most of the affected people are children (MRB 2005). Except wars and natural disasters, malaria is the cause of 50% of the mortalities since prehistoric times (Kevin 2005).

It is well known that mosquitoes suck blood from different animal hosts and transmit mosquito-borne diseases like encephalitis, malaria, elephantiasis (filaria), yellow fever, dengue fever and JE to humans (Reiter 2001). A virus of Bunyaviridae family and Phlebo genus transmitted by mosquitoes causes a common disease to human and livestock in the worldwide (Hunter 1994; Obi 2004; Yakubu & Singh 2008).

The small red house mosquito (Culex tritaeniorhynchus Giles) sucks blood from livestock carrying JE, causing virus pathogens, and transmits JE into humans' blood during sucking blood from a human (Yi & John 1983). In South Korea, malaria, JE and elephantiasis diseases were found because of the mosquitoes that carry those disease pathogens (Reiter 2001). Most of the diseases caused by mosquitoes are zoonotic in nature and are transmitted from humans to animals or from animals to human beings.

Livestock have always suffered by bites of various arthropod parasites, which may directly affect their body weight loss, milk production, quality of meat and quality of leather and wool; they also cause abortion and death of livestock (Steelman 1976). Livestock farmers are affected by livestock abortion and young animals' stillbirth and malformation, which are caused by the transmission of mosquito-borne diseases, such as bovine ephemeral fever, Akabane disease, tuberculosis, acute fever, respiratory problem and digestive disorders. To reduce the incidence of JE transmission from animals to human beings, we should prioritise controlling the mosquitoes (Yi & John 1983). Therefore, our major focus is to develop appropriate control methods to minimize those problems.

More than 3500 species of mosquito have been identified in the world (Reiter 2001). Many female mosquitoes need to suck blood from other animals to develop and lay viable eggs (Richard et al. 2000; Reiter 2001). If there are more livestock, mosquitoes are found in abundance. Such abundance increases the chances of transmitting pathogens to animals and to men (McClelland 1980; Yakubu & Singh 2008).

Generally, it is well known that mosquitoes are easily attracted towards higher concentration of CO₂, which is the product of animals' respiration (Rudolfs 1922; Reiter 2001; Silver 2008). The CO₂ concentration is a good cue to find out animal hosts by the female mosquitoes (Quarles 2003). It has been reported that a human or the same-sized animal emits 250 ml CO₂ in one minute (Reeves 1953; Laporta & Sallum 2011). A western African mosquito species can detect CO₂ from a 15–30 m distance, but this ability to detect CO₂ depends on mosquito species (Gillies & Wilkes 1969; Silver 2008). Headlee (1934) and Silver (2008) reported that they were able to trap 400–500% more mosquitoes using a New Jersey light trap with a provision of CO₂ in evenings within two hours.

Mosquito-borne diseases can be controlled by eliminating mosquitoes, keeping the yard clean and healthy, avoiding the places of growing mosquito larvae around the cowshed and proper management of manure in cowshed (Lawler & Lanzaro 2005). Although an alternative way to control mosquitoes is the use of pesticides, this method can contaminate the environment and also affect livestock and human health. Frequent and haphazard use of pesticides for the eradication of mosquitoes do not kill all the mosquitoes but it may have a big impact in ecosystems through the eradication of other non-targeted species and destroys the food chain structure of the ecosystem (Federighi 2008). Insecticidal resistance of mosquitoes is becoming 12 times stronger and their resistance has more developed during the past 20 years (Kevin 2005). Because of the overutilization of pesticides, the environment has become more polluted and the natural enemies of mosquitoes have decreased (Lee & Yu 1999). Therefore, the use of eco-friendly mosquito traps must be the best practical way for controlling mosquitoes in a cowshed. This study also attempts to test mosquito control efficiency of Mos-hole trap to find if this new mosquito control method is more eco-friendly, without the use of chemicals in a cowshed area.

The purposes of this study were to (1) control mosquitoes in a cowshed by using a new mosquito trap, called Mos-hole trap, which was developed for mosquito control in human living areas, (2) test out the efficiency of the new method to control mosquitoes in a cowshed and (3) study the attraction of mosquito towards Mos-hole traps at different levels of CO₂emission. We hypothesized that the higher CO₂ would attract more mosquitoes and this new method could be the best possible way to control mosquitoes in a cowshed.

Materials and methods

The study site

The cowshed site (called Daengal, 37° 17′ 30″ N, 127° 38′ 28″ E) is located in Buknae-myeon Oeryong-ri, Yeoju-gun in Gyeonggi-do of South Korea. The study site is covered by forests in almost all sides. The average annual temperature is 12°C and the average temperature from May to August is between 17°C and 26°C.

Materials and sampling

A preliminary survey was done on 18 May to facilitate the whole study and to find out the outside circumstances of a cowshed. Twelve Mos-hole traps (350 mm diameter and 400 mm height; E-TND Co., Hanam, Gyeinggi-do of South Korea) were set up around the cowshed (Figure 1). The Mos-hole trap contained stainless steel frame and was coated by fabric clothing outside. It also had rain block cover at the top of the trap. Mosquito suction barrel was at the central top part of frame. A mosquito catch bag was assembled at the lower part of the suction barrel to keep the mosquitoes trapped. The lower end of the inside case was fitted with a suction fan and connected with electric power (220 V) for creating suction pressure to suck mosquitoes and to release mosquito attractant outside. Liquid naphtha bottles (1000 ml bottle in each trap) were used inside the traps to release low proportion of CO₂. The compressed CO₂ cylinder was kept outside for releasing high proportion of CO₂. Both the source of CO₂ release technique and the liquid naphtha system to create CO₂, H₂O, humidity and heat were used to attract mosquitoes. The traps were kept at ground level and installed approximately at 5m distance from the wire screen of the cowshed. This study was carried out from 18 May to 10 July 2012 (54 days) and we used two different CO₂ emission concentrations (35–100 ml/minute and 500 ml/minute) to know the optimum CO₂ concentration at the cowshed.

Figure 1. Experimental design about the mosquito study shows that 12 mosquito traps were installed around the cowshed. Each number in circle shows 12 Mos-hole traps around the cowshed. The distance of each trap was approximately 15 m and the distance from cattle shed wire border was about 5 m. Other environments around new cowshed were old, abandoned cowshed, used tires, small stream and water reservoir.

The study was conducted by applying three different treatments (details in Figure 2). In the first treatment, all 12 mosquito traps were baited with 35–100 ml/minute emission (low proportion) of CO₂ from first turn to ninth turn (18 May to 18 June) by burning and combusting liquid naphtha (1000 ml bottles) kept inside at the bottom of the Mos-hole trap (Figure 2A). In the second treatment, the emission of CO₂ was increased to 500 ml/minute by using six CO₂-compressed cylinders in even-numbered traps (Figure 2B). In the odd-numbered traps, the same low proportion CO₂ emission of the first treatment was maintained. The second treatment was applied from 10th turn to 13th turn (21 June to 4 July) to examine the differences in trapped mosquito population size between low proportion CO₂ and high proportion CO₂ emission. In the third treatment (10 July), 500 ml/minute of CO₂ was emitted at all odd- and even-numbered traps by using 12 compressed cylinders of CO_2. The CO₂ emission pressure was constantly maintained by the pressure regulator during the whole study.

Figure 2. Experimental design of three different treatment levels (I, II and III) about mosquito study: (I) CO₂ concentration, 35–100 ml/minute in all 12 traps in first nine turns (18 May–18 June) by using liquid naphtha as source of CO₂; (II) CO₂ concentration, 35–100 ml/minute in all odd-numbered traps (six traps) and 500 ml/minute in all even-numbered traps (six traps) of 10th to 13th turns (18 June –4 July, lower and upper graph line) by using liquid naphtha and CO₂ cylinders as sources of CO₂; (III) CO₂ concentration, 500 ml/minute in all traps (12 traps) of 14th turn (July 10, upper graph line, last turn) by using CO₂ cylinder as source of CO₂.

In each turn, all samples were collected and a new catch bag was replaced. The status of power supply and the amount of CO₂ emission were checked. Mosquito samples collected were brought to the laboratory of Seoul Women's University for species' identification and counting the mosquito numbers under stereo microscope. Identification of mosquito species was followed by the morphological identification keys (Casse et al. 1950; Ree 2003; Varnado et al. 2012).

Statistical analysis

The number of mosquitoes collected per day per trap was calculated by dividing each turn of total mosquito numbers by numbers of traps used and the duration of sampling days (Table 1). Shannon Wiener's diversity index (H), richness (S) and evenness (E) were determined by using PC-Ord version 4.0 (McCune & Mefford 1999; McCune & Grace 2002).

Table 1. Taxa table of mosquito and average number of mosquitoes per day per trap at three phase stages (I, II, III).

Phase		I								II								III
										21 June		26 June		02 July		04 July		10 July
Mosquito taxa	21 May	25 May	28 May	02 June	05 June	08 June	14 June	16 June	18 June	No CO2 tank	Co2 tank	No CO2 tank	CO2 tank	No CO2 tank	Co2 tank	No CO2 tank	Co2 tank	All CO2 tank	Total
Duration of sampling (days)	3	4	3	5	3	3	6	2	2	3	3	5	5	6	6	2	2	6
No. of mosquito traps used (n)	12	11	12	11	12	12	11	12	10	6	6	5	6	6	6	6	6	11
No. of disturbed mosquito traps (n)	–	1	–	1	–	–	1	–	2	–	1	1	–	–	–	–	–	–
Aedes albopictus Skuse	0.31	0.05	0.31	0.62	0.19	0.39	0.21	0.13	0.25	0.11	0.22	0.12	0.2	0.56	0.42	1.33	1.33	0.58
Aedes bekkui Mogi	0.03	–	–	–	–	–	–	–	0.10	–	–	–	–	–	–	–	–	–
Aedes hatorii Yamada	–	–	–	–	0.08	–	–	–	–	–	–	–	–	–	–	–	–	–
Aedes vexans nipponii Theobald	2.64	3.73	2.36	1.22	1.61	3.69	1.68	7.38	27.5	8.94	51.67	11.28	219.00	14.42	73.64	10.58	171.75	91.38
Other Aedes	–	–	0.11	–	–	–	–	–	–	–	–	–	–	–	–	–	–	–
Anopheles lesteri Baisas and Hu	0.08	0.02	0.06	–	0.03	0.31	0.24	0.38	–	0.22	1.50	1.20	8.23	1.03	1.81	0.42	1.58	0.65
Anopheles sinensis Wiedemann	0.22	0.34	0.14	0.04	0.67	0.44	0.11	1.21	2.50	0.67	1.17	0.28	3.40	0.64	0.61	1.17	1.58	2.09
Anopheles sineroides Yamada	–	–	–	0.02	–	–	–	0.04	–	–	–	–	0.07	–	0.25	–	–	0.09
Anopheles yatsushiroensis Miyazaki	–	–	–	0.04	–	–	–	–	–	–	–	–	–	–	–	–	–	0.08
Other Anopheles	–	–	0.06	–	–	–	–	–	–	–	–	0.08	–	–	–	–	–	–
Armigeres subalbatus Coquillett	–	0.34	0.33	0.47	1.03	1.06	0.97	1.75	1.30	0.28	0.39	0.04	0.87	0.28	0.25	0.08	1.08	1.77
Culex orientalis Edwards	–	–	–	–	–	–	0.06	0.04	–	–	0.22	0.12	0.27	–	–	0.08	0.33	0.06
Culex pipiens pallens Coquillett	0.03	2.07	1.00	3.22	1.89	7.72	7.26	19.00	20.80	14.28	35.44	21.28	43.97	19.22	12.42	28.17	69.67	28.53
Culex pseudovishnui Colless	0.03	–	–	–	–	–	–	–	–	–	–	–	–	–	–	–	–	–
Culex tritaeniorhynchus Giles	0.64	–	0.83	0.24	1.92	2.31	–	–	0.05	–	–	–	–	–	0.08	–	–	–
Culex vagans Wiedemann	–	–	–	–	–	–	–	–	–	–	–	–	0.03	–	–	–	–	–
Mansonia ochracea Theobald	–	–	–	–	–	–	–	–	–	–	–	–	0.03	–	–	–	–	–
Tripteroides bambusa Yamada	–	–	–	–	–	–	–	–	–	–	–	0.04	–	–	–	–	–	–
S	8	6	9	8	8	7	7	8	7	6	7	9	10	6	8	7	7	9	18
E	0.534	0.584	0.723	0.628	0.811	0.728	0.519	0.493	0.507	0.501	0.444	0.404	0.291	0.545	0.294	0.46	0.378	0.346	0.317
H	1.109	1.047	1.588	1.307	1.687	1.416	1.011	1.025	0.986	0.899	0.864	0.888	0.669	0.977	0.612	0.894	0.736	0.761	0.916
D	0.523	0.570	0.722	0.635	0.793	0.684	0.490	0.531	0.566	0.526	0.521	0.510	0.344	0.557	0.303	0.481	0.438	0.415	0.491

Note: Phase I, first nine turns, shows the number of mosquitoes per day/trap when CO₂ was released at the rate of 35–100 ml/minute in all traps by combusting liquid naphtha (LN). Phase II, 10th to 13th turns, shows the number of mosquitoes attracted per day/trap in two kinds of CO₂ concentrations: no CO₂ tank and CO₂ tank; in odd-numbered traps CO₂ was released at the rate of 35–100 ml/minute through combustion of LN and in even numbered traps, CO₂ was released at the rate of 500 ml/minute by using compressed gas cylinders. Phase III, 14th turn, shows the number of mosquitoes attracted per day/trap when CO₂ was released at the rate of 500 ml/minute in all traps by using compressed CO₂ cylinders. This study has been conducted at Yeoju, and the study period was from 18 May to 10 July 2012. We calculated the richness (S), evenness (E), Shannon Wiener's diversity index (H) and Simpson's diversity index (D).

Results

Abundance and diversity of mosquitoes

We collected 31,715 mosquitoes from 161 mosquito samples collected during 54 days of study period. We found six kinds of mosquito genus in the samples. The genus composition consisted of Aedes (64.531%), Culex (31.107%), Anopheles (3.241%), Armigeres (1.114%), Tripteroides (0.004%) and Mansonia (0.003%). We identified 16 species of six genera. Sixteen species compromised Aedes vexans nipponii (63.838%), Culex pipiens pallens (30.445%), Anopheles lesteri (1.609%), Anopheles sinensis (1.566%), Armigeres subalbatus (1.114%), Aedes albopictus (0.664%), Culex tritaeniorhynchus (0.550%), Culex orientalis (0.107%), Anopheles sineroides (0.043%), Aedes bekkui (0.012%), Anopheles yatsushiroensis (0.011%), Aedes hatorii (0.007%), Tripteroides bambusa (0.004%), Mansonia ochracea (0.003%), Culex pseudovishnui (0.003%), Culex vagans (0.003%), unidentified Anopheles (0.013%) and unidentified Aedes (0.010%) (Figure 3). The number of species in each genus was as follows: five of Culex, four of Aedes, four of Anopheles, one of Armigeres, one of Tripteroides and one of Mansonia. Some of the Anopheles and Aedes mosquito species could not be identified because of the development of fungus in samples contaminated with rainwater. We found that only 3% mosquitoes had sucked blood and 97% mosquito had not sucked blood, out of the total number of 31,715. The total species' richness (S) was 18, evenness (E) was 0.317, the Shannon Wiener's diversity index (H) was 0.916, and Simpson's diversity index (D) was 0.491 (Table 1).

Figure 3. Species' composition (%) of mosquitoes found in sampling in cowshed of Yeoju during the study period (18 May to 10 July 2012).

Additional CO₂ emission

We found positive relationship and significant effect between the increased proportion of CO₂ emission and the number of mosquitoes trapped. In the first phase treatment stage (I), from first turn to ninth turn (21 May to 18 June), we used low proportion CO₂ emission (35–100 ml/minute) and we found 3.98, 6.55, 5.2, 5.37, 7.42, 15.92, 1.15, 29.93 and 52.5 mosquitoes day/trap. We observed steady increments of mosquito population along each turn (Figure 4). Before we studied the second phase treatment stage (II), from 10th to 13th turn (June 18 to July 4), we found that many mosquitoes still existed around the cows and we decided to increase amount of CO₂ (500 ml/minute) emission in even-numbered traps. The number of mosquitoes trapped in each turn was 90.61, 275.06, 89.48 and 247.32 day/trap, respectively. However, the number of mosquitoes trapped in odd-numbered traps (no additional CO₂ emission) at the same turns was 24.5, 34.43, 36.15 and 41.83 day/trap. Our result showed that 5.2 times more mosquitoes were caught at the increased CO₂ emission traps than at the low proportion of CO₂ traps (ANOVA, Pr >F = 0.0299). In the third treatment phase stage (III), 14th turn (July 10), we used 12 traps with increased CO₂ emission (500 ml/minute) and the mosquito population was 125.23 day/trap. When we used increased CO₂ (500 ml/minute) emission in the traps, we caught higher mosquito population at each turn.

Figure 4. Trapped mosquito population with different levels of CO₂ released: The graph line is showing the number of mosquitoes attracted per day/trap; phase I – In the first nine turns, release of CO₂ at the rate of 35–100 ml/minute in all traps by combusting liquid naphtha (LN); phase II – The lower graph line in 10th to 13th turns shows the number of mosquitoes attracted per day/trap in odd-numbered traps, when CO₂ was released at the rate of 35–100 ml/minute through combustion of LN; upper graph line from 10–13 turns shows the number of mosquitoes attracted per day/trap in even-numbered traps, when CO₂ was released at the rate of 500 ml/minute by using compressed gas cylinders; phase III – The upper graph line in 14th turn shows the number of mosquitoes attracted per day/trap, when CO₂ was released at the rate of 500 ml/minute in all traps by using compressed CO₂ cylinders. The schemes of phase I, phase II and phase III are shown in Figure 2.

Discussion

Controlling mosquito population by using CO₂-baited Mos-hole trap in a cowshed is a relatively new technology. Knowing the biology, behavior and ecology of mosquito species is the most basic requirement for the successfulness of the mosquito control program. Mosquitoes have greater diversity, higher breeding capacity and greater efficiency to travel long distances, which poses problems for their effective control. Kline (2006) states that if there is higher biotic potential and higher population density of mosquitoes, they could not be reduced to a minimum level by using only traps. In our study, the use of high proportion (500 ml/minute) of CO₂ as attractant in combination with H₂O, humidity and heat-release mechanism in the Mos-hole traps was found to be more effective for attracting and catching a large number of mosquitoes rather than low proportion release (35–100 ml/minute) of CO₂ with similar mechanism. Among the sampled mosquitoes, we identified six genus with 16 species (2 species cannot be identified) during the period of study (Figure 3). Among the 16 species, Aedes vexans nipponii, which is active for seeking host specially in day time, and Culex pipiens pallens, generally nocturnal in behavior (Bockarie et al. 2009), have shown highly dominant response (63.84% and 30.45%) towards CO₂-baited Mos-hole trap. Trout et al. (2007) and Trout and Brown (2009) also reported similar results that a majority of Aedes species were trapped under CO₂-baited light traps (without the light), and traps under tree canopy catch more Culex species in CO₂-baited light traps (without the light) at ground level. Our study result showed similar trend as found by Trout et al. (2007). Likewise, Anopheles sinensis and Anopheles lesteri, which are active at dusk or, dawn or, night (Bockarie et al. 2009), and Armigeres subalbatus, active during both day and night (Das et al. 1971; Rudra et al. 2013), have shown mildly dominant (1.57%, 1.61% and 1.11%, respectively) response towards CO₂-baited Mos-hole trap. The positive response of Aedes vexans nipponii, Culex pipiens pallens, Anopheles lesteri, Anopheles sinensis and Armigeres subalbatus species towards CO₂-baited traps suggests us that CO₂-baited Mos-hole trap is efficient for controlling these species of mosquitoes. However, Aedes albopictus, Culex tritaeniorhynchus, Culex orientalis, Anopheles sineroides, unidentified Anopheles (other Anopheles), Aedes bekkui, Anopheles yatsushiroensis, unidentified Aedes (other Aedes), Aedes hatorii, Tripteroides bambusa, Mansonia ochracea, Culex pseudovishnui and Culex vagans (0.664%, 0.550%, 0.107%, 0.043%, 0.013%, 0.012%, 0.011%, 0.010%, 0.007%, 0.004%, 0.003%, 0.003% and 0.003%, respectively) showed poor dominant response (Figure 3). The actual cause of less attraction of these species is unknown. Further investigation with different levels of CO₂ emission and study of other outside circumstances regarding their habitat, biology and abundance in the study site are essential to find out the actual cause.

We used three kinds of treatment to find out mosquito attraction towards the CO₂-baited traps. In the first treatment, the lower rate (35–100 ml/minute) emission of CO₂ was applied in all 12 traps. Emission of this lower amount of CO₂ appears to be insufficient in catching higher number of mosquitoes. A steady increase of CO₂ emission has seen an increase in trapped mosquito population (Figure 4) during the period. Even though the trend of increase in trapped mosquito population is minimal, the result showed that the release of CO₂ has positive response towards trapping of adult female mosquitoes. In the second treatment, comparative study was done by applying low proportion of CO₂ in six odd-numbered traps and high proportion of CO₂ (500ml/minute) in even-numbered traps to find out the mosquito catch efficiency of the traps. Increased emission rate (500ml/minute) of CO₂ was nearly equal to the breathing of cows (emission of CO₂ at 250 ml/min is similar to that of an human-sized animal; Reeves 1953; Laporta & Sallum 2011), which had a significant effect in capturing adult female mosquitoes. A positive relation was seen in increased proportion of CO₂ and the captured number of mosquito population. The number of mosquitoes captured is 5.2 times more in additional CO₂-emitted traps (83.8% mosquitoes) than in traps that did not emit additional CO₂ (16.2% mosquitoes). In the third treatment, increased rate of CO₂ was applied (500ml/minute) in all traps; it was found that trapped mosquito population increased significantly as compared to previous stages (Figure 4). Headlee (1934) found that the use of CO₂ in combination with mechanical trap increased the number of mosquito catches. Our study is also very close to that of Headlee (1934). Therefore, use of CO₂ at 500 ml/minute might be one of the good non-chemical options for controlling mosquitoes' population in a cowshed.

Our study further reveals that the emission of higher rate of CO₂ also improves in catching blood-sucked population of mosquitoes. The captured mosquito specimen consisted of 3% blood-sucked population. Mosquitoes that feed on blood have the potentiality for transmitting diseases. Parasites use mosquitoes to complete some part of their life cycle where they multiply or change their form. After a mosquito lays her eggs, she seeks a host for another blood meal and transmits the fully grown parasites to other animals or human beings and vice versa. A female mosquito can lay 200–300 eggs at a time and 2–3 times in her life cycle after getting a blood meal. In a generation, a female mosquito can produce approximately 500 mosquitoes. We collected 794 blood-sucked mosquitoes during our study. If they got to produce offspring, then approximately 397,000 mosquitoes would have been produced and these 397,000 mosquitoes would have produced 19.85 billion mosquitoes within a three-month period of their life cycle. Therefore, capturing of blood-sucked population of mosquitoes in CO₂-baited Mos-hole traps is another additional advantage in the field of mosquito control and control of mosquito-borne diseases in livestock as well as in human beings.

The result found by testing new technology to control mature female mosquitoes, by using CO₂-baited MOS-hole traps, in this study is found encouraging. We could use this mosquito control method both in cowsheds and in home areas. This technology is more eco-friendly than that of many chemical control methods, because it causes less environment pollution and less health hazardous effects in human beings as well as in animals. Chemicals have environment pollution effect, resurgence problem of pests and resistances developed against chemical in the pests while using it to control them. Moore et al. (1990) also indicate that gravid Culex mosquitoes may not be affected by the use of pesticides to control them. However, the successfulness of the CO₂-baited Mos-hole traps for trapping mosquitoes depends on many other physical environment and geographical situations of the study place. In the context of this study, some of the unfavorable situations like a small water stream in three sides of the shed, with stagnant water at various places near to it, greatly provide favorable condition for laying eggs and larvae growth of mosquitoes. Likewise, storage of a big heap of waste tires and storage of agricultural by-products for cattle near the cowshed favors mosquitoes by providing resting place. On the other hand, grown-up weeds in the periphery of the shed and thick forests in 40–200 m distance in all sides provide harbour for good resting, laying, and growing atmosphere for mosquitoes from which a big number of adult mosquitoes come out on regular basis.

Therefore, it seems essential to manage all outside circumstances that harbour mosquitoes for getting full effectiveness of the technology. Therefore, an integrated approach like destruction of mosquitoes' resting places like weeds, clearing stagnant water to avoid laying eggs, stall cleaning, safe storage of agricultural products and cleaning the periphery of the yard may help in increasing the effectiveness of the technique and can decrease mosquito population. A single approach of control might not be fully effective for controlling them.

Conclusion

The study of new technology about mosquito control presented in this article has some positive aspects and some shortcomings. This technology exhibits positive response in catching several mosquito species of Aedes, Culex, Anopheles and Armigeres. Higher level (500ml/minute) emission of CO₂ might be a reliable substitute to control adult female mosquitoes in cowshed areas. In case of lowly attracted species, we need to know all the behavioral aspects and abundance of those mosquito species in the study site. It is necessary to conduct more research to find out the species-specific response towards CO₂ for lowly attracted species of Aedes, Culex, Anopheles, Tripteroides and Mansonia. We further suggest consideration of other circumstances nearby the study site, if they harbour mosquitoes. We recommend the use of an integrated approach to control mosquitoes in such a situation.

Acknowledgements

This study was supported by research grants from Seoul Women's University.