Distribution of Aedes aegypti and Aedes albopictus In Zones 1-4 of the Ala Wai Canal
Team Rocket
Kelsey Hung, Nicki Silva, Jaime Rosenberg, Shannon Yoshikawa
Question:
What is the population density of the Aedes aetgypti and Aedes albopictus species of mosquitos found in zones one through four of the Ala Wai Canal and how does this affect the surrounding life?
Project Background:
Our group decided to survey the first four zones of the Ala Wai, starting at the bridge on Date street and down to the boat launching dock, to find out which species of mosquitoes were found there, as well as an approximation of the density of each species in the areas surrounding our school. The two prominent, non-native species of mosquito that we focused on were the Aedes aegypti (the yellow fever mosquito) and Aedes albopictus (the Asian tiger mosquito). It was important to monitor and record the movement of the population of these mosquitoes because they were both vectors, meaning that they could potentially carry disease-causing organisms and spread them to the people with whom they came in contact with (Vector, 2004). Specifically, the Aedes aegypti can spread yellow fever and the Aedes aegypti can be a carrier of the Dengue virus. In addition to being harmful to humans, infected mosquitoes can be harmful to other animals such as native birds (Leong, 2010).
In 1826, the first mosquitoes that arrived in Hawai’i were night-biters. However, the first day-biting mosquitoes did not come until sometime between 1892 and 1897 (Vector, 2004). The first among those included the Aedes aegypti and Aedes albopictus (Leong, 2010). In the early 1900’s these two species of mosquitoes caused alarming outbreaks of yellow fever and Dengue fever around the state. In the mid 1960’s, major efforts were taken to eradicate Aedes aegypti from the state of Hawai’i. Although most of the effort was successful, today there is still a population of Aedes aegypti found exclusively on the Big Island of Hawai’i. Unfortunately, those mosquitoes can easily be brought to the other islands by means of shipment or travel, so it is important that their presence is constantly monitored on outer islands.
Both the Yellow Fever and Asian Tiger mosquitoes breed in areas with ready access to fresh water, which is where they lay their eggs. They prefer objects such as old tires, which can hold stagnant water, where their eggs will not be disturbed (Leong, 2010). Mosquitoes develop in a four stage life cycle called complete metamorphosis. The cycle starts when a mature female lays the eggs, which are either single or stuck together. The eggs eventually hatch and are considered to be in their larval stage, also known as “wrigglers.” During the wriggler stage the larvae live in the water. Next is the pupal stage, which also is an aquatic stage. Finally, the adult mosquito pushes out of the pupal casing and is fully developed and ready for their first meal (Leong, 2010).
In the past, the yellow fever mosquito has been the cause of yellow fever and Dengue fever epidemics. Past efforts to extinguish the species in the United States have failed, leaving the yellow fever mosquito still present across America. During the summer, they are active in the north, but in the south, they are active year round (Womack). The larvae take anywhere between 4 and 10 days to complete development, depending on environmental conditions (temperature, food supply, etc.). They live in towns and cities where their human food sources are nearby. They are not known to wander far from their breeding sites (Womack).
The Asian tiger mosquito also has the ability to carry and transmit Dengue fever. Its larvae are known for their aquatic development in small amounts of stagnant water, and have been reported to develop fully in only ¼” of water (Crans).
Mapping out zones one through four of the Ala Wai’s mosquito population will be helping a larger project that is already in action. On the Big Island, West Hawai’i Explorations Academy is also taking part in surveying areas and recording where these mosquitoes are abundant. By doing this, we will be pinpointing what sorts of environments the mosquitoes prefer and thrive in. By gaining further knowledge, we are hopeful that in the long run we can identify which environments to be wary of, so mosquitoes do not get the opportunity to breed.
The types of traps we used are called MosquiTraps, and they are black cylindrical containers that hold water in the bottom and sticky paper in the upper part. The trap works by attracting the mosquitoes with the water or bait. Once the mosquitoes fly inside the trap, they are surrounded by a wall of sticky paper on either side of them because it is also in the shape of a cylinder. The mosquitoes get stuck on the sticky paper and then we can identify them under a microscope when we collect our traps. The trap also has a cone shaped top that allows a wide base for the mosquitoes to fly into but makes it difficult for the mosquitoes to find their way out of the trap. One of the challenges that we had with this trap was that the sticky paper became loaded with debris and many other types of insects besides the mosquitoes. It was difficult to distinguish between the mosquitoes and gnats at times, especially when the bodies were slightly degraded. Another challenge that we had with the trap was being able to determine how much water was necessary in order to attract the mosquitoes to lay their eggs.
By locating places where these two mosquito species are abundant, we can also be proactive about keeping their numbers down and assuring their population does not have significant increases. We deployed four traps along the Ala Wai Canal throughout zones one, two, three and four. We also deployed one in Manoa near the Manoa stream. Taking into consideration a mosquito’s ideal environment, we placed the traps in areas close enough to the water, but high enough so that they would not be disturbed at high tide. We also tried to camouflage the traps by covering them with dried leaves or placing them in between tree branches. Unfortunately, our camouflages did not prevent trouble makers from disturbing a few of our traps and destroying data. The first trap we deployed was just on the right side of the boat ramp. Both times that trap was stolen or disturbed. The second trap was in front of the “One Team” sign on the fence of the tennis courts. The third trap was deployed in front of the lower school auto line beneath some bramble. The final mosquito trap we deployed in school was planted about fifty feet makai of the bridge on Date Street.
Map of the Ala Wai, we planted traps in zones 1-4
http://www.sealancers.org/Maps/alawai.gif
The MosquiTrap we used to collect our data
http://www.ufmg.br/online/arquivos/Dengue_armadilha-thumb.jpg
A mature Aedes aegypti, also known as the Yellow Fever mosquito
(
A diagram on how to identify an adult Yellow Fever mosquito
(
A mature Aedes albopictus, also known as the Asian Tiger mosquito
(http://www.mosquito-va.org/images/asian_tiger_mosquito_02.jpg)
Picture of Aedes aegypti under a microscope
Picture of Aedes albopictus under a microscope
Materials and Method:
Materials:
MosquiTrap (4-5)
Beakers
Light micoscope
Fly Nap
Mosquito bait, AtrAedes Lure
Tape and Cling Wrap
Method:
1. Go survey the zones of the Ala Wai to determine safe, secure places to set the traps
2. In the meantime, we can go out and collect larvae to identify and record
3. Put the traps out when they arrive and leave them out for a designated amount of time
4. Bring traps back to the lab and make sure the mosquitoes inside are immobilized or dead before opening it up to examine the species present
5. Identify and record the number of each species in each zone as well as the environmental conditions of the area the trap was left
6. Analyze data to conclude the environment in which each species is most abundant
7. Repeat process for trap taken to Manoa Stream
Data:
Date / Trap #1 / Trap #2 / Trap #3 / Trap #4 / Trap #5 (Manoa)TRIAL 1
3/16 – 4/ 2
(17 Days) / All data stolen / Asian Tiger: 2
Yellow Fever: 2 / Asian Tiger: 6
Yellow Fever: 3 / Asian Tiger: 26
Yellow Fever: 0 / Asian Tiger: 1
Yellow Fever: 0
TRIAL 2
4/2 – 4/19
(17 Days) / All data stolen / Asian Tiger: 4
Yellow Fever: 1 / Asian Tiger: 4
Yellow Fever: 0 / Asian Tiger: 33
Yellow Fever: 0 / All data stolen
Discussion:
From our data, it seems like there is not a very large mosquito population surrounding our school and the Ala Wai Canal. The trap that yielded the most mosquitoes overall was trap #4, which was placed in zone one of the Ala Wai up by the bridge on Date Street. It is unfortunate that our trap #1 was tampered with and stolen during both trials, because that is the zone closest to our campus so it would have been interesting to see how many mosquitoes would have been present. It is very interesting that all the traps that yielded mosquitoes had significantly lower numbers than the trap in zone one. It would be intriguing to know why there were more mosquitoes present in that area than in the other zones where the traps were deployed.
A factor that may have affected the number of mosquitoes yielded is that trap #4 was in a slightly different environment than the other traps deployed at school. Trap number four was higher above the water level and was on the side of the walkway, whereas the other traps were more in the plants and closer to the water level. This factor may have been the cause of the deviation of mosquitoes yielded. There was also a homeless man that lived near that area whereas the other sites of deployment were more secluded.
The mosquitoes that we counted in all the traps were either already mature adults when we caught them, or they were in the aquatic larvae form. Because it is very difficult to identify the mosquitoes when they are in their larvae form, we left them in a closed beaker with water and waited until after they hatched to identify them. As adults, they have more distinguishing features that let us more easily identify them using the identification key.
During our second trial of deploying traps, we used mosquito bait, provided by Cory that is called AtrAedes Lure, which is a plant based bait. Employing the bait was expected to increase our yield of mosquitoes, however, based on our data it does not seem like it made a significant difference. We were extremely surprised to find that the bait did not help very much. Cory also said that other organic materials would have served just as well as bait. We also could have used things such as rabbit food pellets. The water in the traps was also meant to attract mosquitoes since all living things need water, and mosquitoes especially seek out stagnant water as an ideal environment in which to lay their eggs. Another factor that may have altered our results in the first and second trials is the weather conditions. During the first trial, there had been a lot of rain, and the extra humidity in the air may have also affected the results. On the other hand, during the time of our second trial, it had been a lot more dry and hot. There may be a possibility that the traps with the bait in a more humid environment would have yielded more mosquitoes than the traps with the bait in the more dry environment they were in.
There is a possibility that errors were made in collecting the data. Because the Asian Tiger and Yellow Fever mosquitoes look very similar, it is possible that some were misidentified or miscounted. From research, we know that the only known population of the Yellow Fever mosquito in the state is on the Big Island, so it is probable that the organisms we identified as Aedes aegypti were not really of that species. Working to differentiate between the two species of mosquitoes was difficult and tedious work, but we learned to pay closer attention to detail and certain prominent characteristics of the individual organisms. The identification key proved to be very helpful in many cases.
Conclusion:
After conducting our experiment of surveying zones one through four of the Ala Wai Canal and analyzing our data, we have learned that there are significantly more Aedes albopictus (Asian Tiger Mosquito) than Aedes aetgypti (Yellow Fever Mosquito) surrounding the Ala Wai Canal. From the data that we collected we can also infer that there is not an immense mosquito population in the area surrounding our school near the canal. We can also conclude that mosquitoes are not necessarily more attracted to water sources with organic material.
There were a lot of factors that we had to take into consideration before deploying our traps and analyzing the data. We had only considered factors like weather and air humidity after we ran both trials. Unfortunately, a substantial amount of our data was lost due to our traps being tampered with and destroyed. However we can safely say that the data we gathered does reflect the mosquito population in the area, and there is not a tremendous population. It is safe to say that our mosquito population is under control and is not under any immediate threat of a population explosion of the vector carrying Yellow Fever and Asian Tiger mosquitoes.
Our experiment is relevant to what is going on right now at WHEA because we are supporting their program of mapping out the geographic distributions of the different mosquito species. This is helping to keep an eye on the vector species as well as study the preferred habitats of both the Aedes aetgypti and Aedes albopictus. By surveying the zones of the Ala Wai here on Oahu, we can also be certain if the Yellow Fever mosquito population is expanding to different islands, since originally it was only prominent on the Big Island. It is important to monitor the population of any species in order to see any trends in increases or decreases and assure that there are no major environmental changes occurring.
If we were to run this experiment again, it would be beneficial to us to conduct more trials in order to obtain more data. We could also experiment with various types of bait and see which attracts the mosquitoes the best. Also, to attempt to eliminate weather as a factor we could try to do the trials in similar weather conditions and for shorter periods of time to assure less of a deviation in the weather and temperatures. For further experimentation we could take this project to another estuary or watershed to see the density of the mosquito populations on different sites on the island. Like we mentioned earlier, because these mosquitoes are vectors, we feel it is important to monitor the populations already established on the island. Even though we ran into a lot of challenges with having to change our experiment entirely and having our data tampered with, all in all we feel that this experiment was a success.
Works Cited:
Crans, Wayne. “Aedes Albopictus.” (2010). Rutgers New Jersey Agricultural Experiment Station
Center for Vector Biology Web Site. accessed Beb 12, 2012.
Leong, Mark and Nelson, John. “Mosquitoes.” (2010). Vector Control Branch Bulletin.
Hawaii Department of Health, Honolulu. Web. 12 February 2012.
“Vector Control Branch.” (2004). Hawaii State Department of Health. Retrieved 12 February
from Department of Health website:
Womack, M. 1993. The yellow fever mosquito, Aedes aegypti. Wing Beats, Vol. 5(4):4.