The white-spotted mosquito and the northern house mosquito are believed to maintain the natural
transmission cycle of West Nile Virus between birds and mosquitoes in Illinois. During the spring
and early summer the white-spotted mosquito, which feeds on birds, is the dominant species and is
responsible for bird-to-bird transmission of WNV. As the weather warms,
the northern house mosquito, the most common night-flying mosquito, becomes
more dominant. The female of this species is probably responsible
for the rapid amplification of the arbovirus among birds and
may act as the major bridge vector to mammals, including humans,
in the Midwest. Two types of climate models have been developed to provide
an estimate of the likely date where the northern house mosquito begins
to become the dominant species, and thus when the risk of WNV to horses,
humans, and other wildlife is likely to increase.
The information provided here is based on recent research conducted by scientists at the Midwestern Regional Climate Center, Illinois State Water Survey and the Illinois Natural History Survey in association with the National Climatic Data Center. This research is described in the following publication:
Kunkel, K.E., R. Novak, R. Lampman, and W. Gu, 2006: Modeling the impact of variable climatic factors on the crossover of Culex Restuans and Culex Pipiens (Diptera Culicidae) vectors of West Nile Virus in Illinois. American Journal of Tropical Medicine and Hygiene, 74, 168-173.
Mosquitos
and West Nile Virus
MAXIMUM TEMPERATURE EXCEEDANCE
MODEL (Threshold of 81°F):
How to Interpret the Model Results
| 81°F MAX TEMP MODEL - CURRENT MODEL RUN: |
8/12/2008 |
| Based on the current model run there is: | |
|
• a 50 percent chance that the crossover date will be later than |
August 6, 2008 |
|
• a 90 percent chance it will be earlier than |
August 6, 2008 |
| • and a 10 percent chance it will be earlier than | August 6 , 2008 |
|
• The current run of the model has a median crossover date of |
August 6, 2008 |
|
• The earliest crossover date projected by the current model run is |
August 6, 2008 |
|
• The latest crossover date projected by the current model run is |
August 6 , 2008 |
Model Run History for the Current Year
| 81°F Max Temp Model | |||||||
| Model Run Date 2008 | Probability that crossover will occur earlier than given date | ||||||
| Earliest | 10 percent | 25 percent | MEDIAN | 75 percent | 90 percent | Latest | |
| 5/6 | 7/7 | 7/23 | 7/29 | 8/8 | 8/18 | 8/27 | 9/28 |
| 5/13 | 7/12 | 7/25 | 7/31 | 8/9 | 8/20 | 8/31 | 10/2 |
| 5/20 | 7/18 | 7/28 | 8/2 | 8/11 | 8/22 | 8/31 | 10/4 |
| 5/27 | 7/23 | 7/30 | 8/5 | 8/13 | 8/25 | 9/5 | 10/4 |
| 6/3 | 7/25 | 7/30 | 8/3 | 8/12 | 8/22 | 8/31 | 9/27 |
| 6/10 | 7/23 | 7/29 | 8/2 | 8/10 | 8/17 | 8/26 | 9/20 |
| 6/17 | 7/24 | 7/27 | 7/31 | 8/6 | 8/14 | 8/20 | 9/15 |
| 6/23 | 7/28 | 7/30 | 8/2 | 8/7 | 8/15 | 8/21 | 9/12 |
| 7/1 | 7/30 | 7/31 | 8/2 | 8/6 | 8/13 | 8/19 | 9/11 |
| 7/8 | 8/3 | 8/4 | 8/5 | 8/10 | 8/14 | 8/22 | 9/7 |
| 7/15 | 8/3 | 8/3 | 8/4 | 8/7 | 8/13 | 8/16 | 9/4 |
| 7/22 | 8/4 | 8/4 | 8/5 | 8/7 | 8/11 | 8/14 | 8/26 |
| 7/29 | 8/5 | 8/5 | 8/5 | 8/7 | 8/9 | 8/13 | 8/24 |
| 8/5 | 8/7 | 8/7 | 8/7 | 8/7 | 8/8 | 8/9 | 8/14 |
| 8/12 | 8/6 | 8/6 | 8/6 | 8/6 | 8/6 | 8/6 | 8/6 |
DEGREE DAY MODEL:
How to Interpret the Model Results
| DEGREE DAY MODEL - CURRENT MODEL RUN: | 8/26/2008 |
| Based on the current model run there is: | |
|
• a 50 percent chance that the crossover date will be later than |
August 22, 2008 |
|
• a 90 percent chance it will be earlier than |
August 22, 2008 |
| • and a 10 percent chance it will be earlier than | August 22, 2008 |
|
• The current run of the model has a median crossover date of |
August 22, 2008 |
|
• The earliest crossover date projected by the current model run is |
August 22, 2008 |
|
• The latest crossover date projected by the current model run is |
August 22, 2008 |
Model Run History for the Current Year
| Degree Day Model | |||||||
| Model Run Date 2007 | Probability that crossover will occur earlier than given date | ||||||
| Earliest | 10 percent | 25 percent | MEDIAN | 75 percent | 90 percent | Latest | |
| 5/6 | 7/7 | 7/23 | 8/1 | 8/11 | 8/24 | 8/30 | 9/19 |
| 5/13 | 7/12 | 7/25 | 8/1 | 8/12 | 8/26 | 9/1 | 9/20 |
| 5/20 | 7/14 | 7/27 | 8/4 | 8/13 | 8/26 | 9/5 | 9/20 |
| 5/27 | 7/16 | 7/27 | 8/7 | 8/16 | 8/28 | 9/7 | 9/20 |
| 6/3 | 7/20 | 7/30 | 8/6 | 8/17 | 8/27 | 9/5 | 9/17 |
| 6/10 | 7/18 | 7/27 | 8/3 | 8/12 | 8/21 | 8/29 | 9/13 |
| 6/17 | 7/19 | 7/26 | 8/2 | 8/11 | 8/19 | 8/26 | 9/11 |
| 6/23 | 7/19 | 7/29 | 8/4 | 8/13 | 8/20 | 8/27 | 9/11 |
| 7/1 | 7/22 | 8/2 | 8/7 | 8/13 | 8/20 | 8/25 | 9/10 |
| 7/8 | 7/29 | 8/6 | 8/10 | 8/16 | 8/21 | 8/28 | 9/6 |
| 7/15 | 8/3 | 8/8 | 8/11 | 8/17 | 8/22 | 8/28 | 9/8 |
| 7/22 | 8/5 | 8/9 | 8/11 | 8/16 | 8/21 | 8/26 | 9/5 |
| 7/29 | 8/9 | 8/11 | 8/14 | 8/18 | 8/22 | 8/26 | 9/5 |
| 8/5 | 8/12 | 8/13 | 8/15 | 8/17 | 8/21 | 8/24 | 9/1 |
| 8/12 | 8/16 | 8/17 | 8/18 | 8/19 | 8/21 | 8/23 | 8/31 |
| 8/19 | 8/21 | 8/21 | 8/22 | 8/22 | 8/23 | 8/24 | 8/29 |
| 8/26 | 8/22 | 8/22 | 8/22 | 8/22 | 8/22 | 8/22 | 8/22 |
These graphs show the results of the individual model runs so far this season. As more of the “actual” weather is included in the model runs (i.e. as the summer progresses) and less “probable” weather (i.e. past climatology) is included, the plots of the dates will tend to converge on the crossover date.
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