Trap Counts

About the Counts

A man checking a New Jersey Light Trap for mosquitos
Vector Control Director Levi Zahn checks a New Jersey Light Trap

The Williston Vector Control District has two different types of traps located throughout the county: New Jersey Light Traps and Carbon Dioxide (CO2) traps. CO2 traps are operated on a weekly to a twice-weekly basis for the purpose of collecting insects for viral testing. CO2 traps are much more sensitive in assessing mosquito population changes than NJLT’s, however NJLT’s have been used for over 50 years and offer a good base line. CO2 traps are also operated for the purpose of collecting insects for viral testing and enhance existing surveillance operations. NJLT’s are only baited with an incandescent light bulb and are therefore less effective in areas where light pollution is bad. Average trap counts for New Jersey Light Traps are provided below.

Since mosquitoes are highly mobile insects and can have a high variability in day-to-day trap collections, spray decisions are often made holistically taking into consideration the mosquitoes behaviors and hypothetical flight ranges. Therefore, management decisions are often not made based on the collections from one single trap over a single night, but are based on a number of traps within an area, often over a period of time. Due to cost and logistical reasons, traps are not placed into every single neighborhood. Exact trap locations are not provided to reduce the potential for theft and vandalism. Additionally, local habitats can drastically change the local abundance of adult mosquitoes.

Treatment blocks are only used as a guide for coordinating mosquito management operations. Borders are arbitrary and are based upon convenient geographic boundaries.

It is beneficial to perform mosquito management operations before mosquito populations reach their peak. Treatments that take place before peak often result in fewer treatments over the duration of a mosquito season.

2022 Trap Counts

Average Mosquitoes per New Jersey Light Trap per Week

Disease Week 20

(5/15 - 5/21/2022)


(5/22 - 5/28/2022)


(5/29 - 6/4/2022)


(6/5 - 6/11/2022)


(6/12 - 6/18/2022)


(6/19 - 6/25/2022)


(6/26 - 7/2/2022)

Williston 4.75 2.02 1.97 10.26 55.13 186.95
Grenora - 0.14 0.57 9.29 61.29 47
Ray 0.00 1.57 1.57 1.26 6.09 60.50

City of Grenora Average Trap Counts

Week 21 (5/22 - 5/28/2022) - Week 25 (6/19 - 6/25/2022)

City of Ray Average Trap Counts

Week 20 (5/15 - 5/21/2022) - Week 25 (6/19 - 6/25/2022)

Williston Average Trap Counts

Week 20 (5/15 - 5/21/2022) - Week 25 (6/19 - 6/25/2022)

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