West Nile Virus Mosquito Crossover Dates

Experimental Data, for Champaign-Urbana Only - 2011

culex pipiens

Culex pipiens - Northern House Mosquito
Photo courtesy Robin McLeod

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.

MAXIMUM TEMPERATURE EXCEEDANCE MODEL (Threshold of 80°F):

How to interpret the model results
81°F MAX TEMP MODEL - CURRENT MODEL RUN: 7/27/2011
Based on the current model run there is:
    • a 50 percent chance that the crossover date will be later than July 28, 2011
    • a 90 percent chance it will be earlier than July 28, 2011
    • and a 10 percent chance it will be earlier than July 28, 2011
    • The current run of the model has a median crossover date of July 28, 2011
    • The earliest crossover date projected by the current model run is July 28, 2011
    • The latest crossover date projected by the current model run is July 28, 2011
Model Run History for the Current Year
81°F Max Temp Model
Model Run Date 2011 Probability that crossover will occur earlier than given date
Earliest 10 percent 25 percent MEDIAN 75 percent 90 percent Latest
5/4 7/8 7/23 7/30 8/8 8/20 8/28 9/30
5/11 7/7 7/22 7/28 8/7 8/18 8/27 9/26
5/18 7/14 7/23 7/29 8/6 8/19 8/28 9/30
5/25 7/15 7/20 7/27 8/3 8/16 8/21 9/22
6/1 7/16 7/20 7/25 7/31 8/7 8/15 9/14
6/8 7/12 7/15 7/18 7/21 7/29 8/3 8/18
6/15 7/20 7/21 7/24 7/28 8/3 8/8 8/25
6/22 7/27 7/28 7/30 8/2 8/8 8/15 9/5
6/29 7/27 7/27 7/28 7/31 8/3 8/9 8/25
7/6 7/28 7/28 7/29 7/30 8/2 8/7 8/25
7/13 7/30 7/30 7/30 7/31 8/2 8/6 8/19
7/20 7/27 7/27 7/27 7/27 7/27 7/27 7/27
7/27 7/28 7/28 7/28 7/28 7/28 7/28 7/28

Graph of 81F Max Temp Model Data

DEGREE DAY MODEL:

How to Interpret the Model Results
DEGREE DAY MODEL - CURRENT MODEL RUN: 7/27/2011
Based on the current model run there is:
    • a 50 percent chance that the crossover date will be later than July 23, 2011
    • a 90 percent chance it will be earlier than July 23, 2011
    • and a 10 percent chance it will be earlier than July 23, 2011
    • The current run of the model has a median crossover date of July 23, 2011
    • The earliest crossover date projected by the current model run is July 23, 2011
    • The latest crossover date projected by the current model run is July 23, 2011
Model Run History for the Current Year
Degree Day Model
Model Run Date 2011 Probability that crossover will occur earlier than given date
Earliest 10 percent 25 percent MEDIAN 75 percent 90 percent Latest
5/4 7/9 7/24 8/2 8/12 8/25 9/3 9/20
5/11 7/8 7/23 7/31 8/11 8/22 8/31 9/18
5/18 7/11 7/23 8/1 8/11 8/22 8/31 9/19
5/25 7/12 7/22 7/30 8/9 8/20 8/30 9/16
6/1 7/14 7/22 7/30 8/6 8/14 8/22 9/10
6/8 7/13 7/18 7/23 7/30 8/7 8/13 8/29
6/15 7/14 7/20 7/26 8/1 8/7 8/11 8/27
6/22 7/16 7/25 7/29 8/3 8/9 8/15 8/25
6/29 7/18 7/25 7/28 8/1 8/6 8/9 8/19
7/6 7/24 7/28 7/29 8/1 8/5 8/10 8/20
7/13 7/26 7/27 7/27 7/28 7/30 8/1 8/9
7/20 7/24 7/24 7/24 7/24 7/24 7/24 7/24
7/27 7/23 7/23 7/23 7/23 7/23 7/23 7/23

Graph of Degree Day Model Data

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.

NOTE: These models were derived from Champaign-Urbana, Illinois data. The threshold temperature may vary regionally.

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