2021 Enhanced Larval Control Program

In 2019 we saw unprecedented levels of EEE in the MetroWest area. 12 CMMCP member communities were designated as “Critical” risk, and an additional 11 were designated as “High” risk for EEE. Several control measures were implemented by CMMCP, the Mass. Department of Public Health and the State Reclamation and Mosquito Control Board in 2019 for risk-reduction including larval control, public education, and both truck-mounted and aerial adulticiding.

In an effort to reduce risk in 2020 from 2 species of mosquito that are implicated in the EEE transmission cycle in either birds or humans, CMMCP performed enhanced larval control operations in the communities designated as “Critical” and/or “High” risk in 2019[1].

In 2021 we will again perform enhanced larval control in communities designated as "Critical" risk in 2019. The mosquito species targeted in these applications are Culiseta melanura and Coquillettidia perturbans. Larvae of these species have unique habits that make Bti less effective in their control. Cs. melanura larvae inhabit the protected areas under root systems in white cedar and red maple swamps called “crypts”. Crypts are domed structures the tree create to raise the root system and be less impacted by consistent high-water levels. These areas offer a protected habitat for these larvae to go through their larval development. Applications of granular or liquid based Bti either by hand or aircraft do not significantly penetrate the crypt habitat, so larval control is poor to non-existent.

Cq. perturbans larvae also have a unique biology; their larvae attach to the root systems of emergent vegetation such as cattails, breathing air through the root system of the plant. Since these larvae do not freely float looking for food like other mosquito species, the Bti bacteria are less available for consumption by the larvae. Most mosquito larvae rise to the surface of the water to breathe air, and descend to the bottom to filter-feed; Cq. perturbans larvae are stationary until they reach pupation and are ready to emerge.   

The product to be employed for control of these 2 species is a biological product called Natular® (the active ingredient is a bacterium called spinosad, Saccharopolyspora spinosa)[2]. 2 certified organic formulations will be used, a short-term (Natular® G) and a 30-day extended release formulation (Natular® G30). Natular® G will be used in Cq. perturbans habitats and should expose these larvae to this bacterium within the effective control window which is 2-3 days. Natular® G30 will be applied over wetland habitat for Cs. melanura larval control. The extended release period should allow for better penetration of this bacteria into the crypt habitats.

Rotary equipment (helicopter) will be used for these applications in areas greater than 5 acres, and follow up treatments by hand or backpack applications will be done in smaller habitats by CMMCP field staff.

Water sampling will occur in Cs. melanura habitat to determine if the product is reaching the crypts[3], and larval mosquito development and subsequent control will also be monitored in these areas. We will track adult mosquito emergence using surveillance traps and other methods in proximity to some of the treated areas to determine if emergence of these 2 species has been suppressed by these enhanced larval control efforts.

Target dates for application will begin May 25 to coincide with weather and appropriate larval life stage. Pesticide labels and OMRI (organic) certifications are available from our office or on our website at https://www.cmmcp.org/pesticide-information/pages/spinosad-saccharopolyspora-spinosa.


  • Cs. melanura (~538 acres)
  • Cq. perturbans (~1,526 acres)




MAP (.pdf)

Cs. melanura habitat acres

Cq. perturbans habitat acres



Ashland 2021 





Grafton 2021 





Holliston 2021





Hopedale 2021 





Hopkinton 2021 





Marlborough 2021 





Milford 2021 





Northborough 2021





Northbridge 2021 





Shrewsbury 2021





Southborough 2021





Westborough 2021











~538 acres

~1,526 acres

A full report will be posted here when ready.

[1] “Critical” – Ashland, Grafton, Holliston, Hopkinton, Hopedale, Marlborough, Milford, Northborough, Northbridge, Shrewsbury, Southborough, Sturbridge & Westborough. 

“High” – Auburn, Berlin, Blackstone, Boylston, Hudson, Millbury, Millville, Sherborn, Stow & Webster

[2] The National Pesticide Information Center, http://npic.orst.edu/ has information on Bti and spinosad

[3] Sampling will be done by CMMCP staff, but testing will be done at the UMASS laboratory in Amherst, MA and the lab at Cornell University in NY.