Norfolk County Mosquito Control Project

Aerial Larvicide Program

click here for town maps showing wetland areas to be treated  

Introduction:

Spring and summer flooding following snow melt and/or heavy rainfall creates a potential each year for significant mosquito larval development in various wetlands across Norfolk County. The predominate species which develop in the spring are Ochlerotatus abserratus, Ochlerotatus excrucians and Ochlerotatus canadensis. In the summer the predominate species following river flooding are Ochlerotatus trivittatus, Aedes cinereus. Aedes vexans, Psorophora ferox and Ochlerotatus canadensis. All of these mosquito species are strong human biters and can create significant nuisance level populations during the late spring and summer months. During certain years some of the summer mosquito species, such as Aedes vexans, may be involved in the transmission of Eastern Equine Encephalitis (EEE) from birds to humans. In an effort to proactively control these aggressive human biting species and in an environmentally responsible manner, the Norfolk County Mosquito Control Project conducts an aerial larval control operation using a product called Bacillus thuringiensis israelensis often referred to as Bti.

Pre-application activities:

The Norfolk County Mosquito Control Project (NCMCP) currently holds a contract with JBI Helicopter Services, Inc. for the purpose of conducting these aerial larval control applications. The Norfolk County Mosquito Control Project has established that if conditions warrant it, the larger wetlands will be targeted with an application of Bti granular (Vectobac Gā) at a rate of 5 pounds per acre during the spring and 7.5 pounds per acre during the summer. Geographic Information System (GIS) Maps showing specific wetlands to be targeted and landing zones (LZs) where the aircraft will be loaded with fuel and insecticide are prepared for the pilots. Infrared as well as color aerial photographs are used by NCMCP for locating potential larval development sites and for delineating habitats on these GIS maps for further field investigations. Personnel from NCMCP are dispatched to dip select wetlands in the targeted towns to determine whether the larval density exceeds the established threshold. The final GIS data is uploaded into the aircrafts Ag-Nav® navigation system which allows the pilot to fly to each specified wetland electronically using a minimum of fuel and airtime. JBI Helicopter Services, Inc. uses this aerial guidance system to accurately record the applications over the targeted wetlands. NCMCP uses this data to compile an accurate record of the application which includes digital maps showing the wetlands treated. Imbedded in this GIS data NCMCP can also retrieve such information as time of application, elevation of the aircraft at time of application, airspeed as well as other parameters which help in analyzing the effectiveness of the overall application.

     The Application:

Once the wetlands are checked and the larval density established a decision is made to conduct an aerial application using Bti granular.  .

The application is conducted using Bell 206B Jet Rangers.

   

The application covers approximately 13,000 acres in total during the spring and as much as 7,000 areas during each summer application.

The spring application is conducted in mid to late April depending on seasonal weather conditions and between the hours of 6:30 AM. and 7:30 P.M. Weather conditions need to be fairly stable with winds not exceeding 12 mph. Summer applications may occur any time during the summer months following heavy rain events. Field personnel visit treated wetlands 48 hours post application to determine efficacy.

Results:

The typical wetlands treated during the spring are described as Palustrine - Forested - Broadleaf and Palustrine - Scrub/Shrub - Broadleaf as delineated on the National Wetland Inventory Maps.

  

Summer applications are more typically conducted over river floodplain areas especially within wetlands adjacent to the Neponset and Charles Rivers.

 

One final note is that the Norfolk County Mosquito Control Project has been able to significantly limit the acreage to be treated because of this intense larval monitoring. From one season to the next there will always be some fluctuation of the acreage treated due to weather related affects to local ground water levels in the targeted areas. 

As part of the Norfolk County Mosquito Control Projects Integrated Pest Management (IPM) procedures, the Project will track complaint calls received from areas adjacent to the larger wetlands across the county to determine which areas may need more intensive larval surveillance during future larval development events.

Once again, coordination with the East Middlesex Mosquito Control Project, the Plymouth County Mosquito Control Project and the Northeast Massachusetts Mosquito and Wetlands Management District was very helpful in determining what the larval development conditions were across the eastern half of Massachusetts.

2004 Pre and Post Data 1                    2004 Pre and Post Data 2                    2005 Pre and Post Data 1                    2005 Pre and Post Data 2

Data shown above is from  RDS sites where Bti granules were present post-treatment.

Control Sites includes data from RDS sites where there was no evidence of Bti granules in surveys conducted post-treatment.

 

Additional application pictures:

[ pic1.jpg | pic2 .jpg | pic3.jpg ]