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| Future Research Interests |
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The CMCD focuses primarily on one mosquito for disease control, Culex nigripalpus. This mosquito is the known vector for Saint Louis encephalitis (SLE) and is believed to be the vector for West Nile virus (WN). In order for the District to develop a better understanding of how well this species is controlled by CMCD applications, as well as the disease transmission capability of Culex populations, the Research Department at the CMCD is interested in collecting and age grading Culex nigripalpus.
Age grading is accomplished by dissecting the ovaries of female mosquitoes and examining them. Similar to the rings on trees, the female mosquitoes' ovaries create "rings" with each batch of eggs laid. The age of the mosquito can be determined by counting the "rings" on the ovaries.
A female mosquito needs a blood meal in order to develop eggs. After the mosquito obtains blood, it takes approximately four days for the mosquito to digest the blood and produce a batch of eggs. The eggs are then laid as soon as a good site is located. Therefore, for every egg batch laid, the mosquito is roughly four days older. The approximate age of the mosquito can be determined by adding up the number of "rings" on the ovaries and multiplying that number by four.
Knowing the age distribution of Culex nigripalpus populations before and after control treatments helps the CMCD to understand the effectiveness of the control. That is, if the Culex populations are primarily older before control and younger after control, then the older adults that may have been ready to lay eggs were killed. However, the young adult populations are not as likely to be capable of laying eggs so soon. The fewer female mosquitoes able to produce eggs mean the smaller the population of Culex mosquitoes and that control efforts are effective.
The age distribution of Culex nigripalpus is also very important to understand for disease transmission. While a female mosquito needs a blood meal to produce eggs, she also needs blood in order to transmit disease. However, the blood would have to already be infected with the virus. In the case of WN and SLE, it takes approximately ten days to two weeks for the virus to incubate inside the mosquito to the point when the disease can be transmitted to another organism through a mosquito bite. Therefore, a mosquito that has already laid several batches of eggs is more likely to be capable of transmitting a disease rather than a mosquito that has only laid one batch of eggs. This is because for every egg batch laid, the mosquito is approximately four days old. If the mosquito has laid three batches of eggs in its lifetime, it could be at least twelve days old. Therefore, if that mosquito had bitten an organism infected with WN during its first blood meal, then it was potentially capable of transmitting that disease to the host of its final blood meal.
The age grading of Culex nigripalpus mosquitoes through dissection will help the CMCD to understand the level of control achieved for the species as well as the potential of the current populations to transmit disease. |
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Projects
