The Chelmsford Board Of Health has released this public notice about aerial spraying for mosquito larvae:

AERIAL APPLICATIONS TO CONTROL MOSQUITO LARVAE

The Towns of BILLERICA and CHELMSFORD will be conducting helicopter applications of the biological larvicide, BTI, to control mosquito larvae between April 15, 2013 and April 25, 2013. The applications will be conducted over specific large wetlands within the two communities. Applications will be done between daybreak and dusk.

Richard J. Day,
Chelmsford Board of Health
Richard Berube,
Billerica Health Department

April 12, 2013

There is an online map of the spray areas [pdf] on the Central Massachusetts Mosquito Control Project website, as well as a description of the process.

Anyone with questions should contact the Chelmsford Board of Health, 50 Billerica Road, Chelmsford, MA 01824, 978-250-5241.