Press release 4/10/12 from the Health Director – aerial Bti application cancelled
Wayland is a participating member of the East Middlesex Mosquito Control Project. The Project provides mosquito control services to 25 participating communities located west and northwest of Boston. Each, spring in April, the Project conducts a Bti larviciding program that consists of aerial spraying of wetlands by helicopter. Bti is a biological larvicide used to control floodwater species of mosquito larvae. On April 4th, the Wayland Board of Health received notification from Dave Henley Superintendent of the Eastern Middlesex Mosquito Control Project that due to the abnormally dry weather of the past 2 months and also in part
the warm weather that we experienced in mid-March, the Project has decided to cancel the spring aerial Bti application. Henley reports that this is the first time that the April Bti application has been cancelled since it started in 1987. There are several weather related factors that have led to this decision. Most of the wetlands have dried down especially in river flood plains and in red maple swamps. In some cases entire wetlands have dried.
According to the Boston Globe as of 4/3/2012, precipitation levels for the calendar year to date are 6.35 inches below normal. From February 1st through April 4th, there has only been 2.32 inches of precipitation.
Typically when wetlands are flooded, Bti is more effective. When wetlands are drier than normal, pools of water gradually recede and the mosquito larvae become more concentrated. When mosquito larvae are more concentrated, then more Bti is needed to effectively provide control. Unfortunately, when wetlands are drier than normal, more of the Bti granules land on dry ground so there is less Bti that actually reaches the water. As a result during abnormally dry conditions, Bti aerial applications are less effective.
Typically there are three or four major mosquito species that comprise the spring mosquito brood. During years when there is flooding between mid April and early May, a fourth species will emerge. The helicopter application is timed to provide control of the first three species. Due to the extraordinary warm weather that we experienced in mid March, the first two species emerged 10 - 14 days earlier than normal. This early emergence has caused a greater separation between the spring species so that one helicopter application would not be able to provide effective control against the three primary spring species. Due to the dry conditions it’s likely that the spring mosquito population will not be a major problem to residents.
The Wayland Board of Health will continue communications with Project personnel as they closely monitor the situation. As part of our program the catch basins in town will be treated this spring (sometime in June) with the larvicide ALTOSID XR Briquettes supplied by the Wayland Board of Health. This catch basin treatment is to reduce the number of the culex mosquitoes, which are known to reproduce in a catch basin type of environment. The culex species are also known as “bridge” vectors that will feed on birds and people. Throughout this season we will continue to post mosquito control updates on the Health Department website and to other information sources as it is available to us.
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