Week 34 – Aug 19 – 20

2009 Mosquito Report: Week 34

Report based on data collected from traps deployed on Wednesday, August 19, 2009 and retrieved on Thursday, August 20, 2009. Report prepared by John Smith, Chan Suom, M.S., and Nate Boonisar.

1. Current mosquito activity/trend

CDC Light Traps:
Host-seeking mosquito activity was mixed in Norfolk County. Avon and Sharon were mixed with parts reporting higher than average counts, and other sections reporting lower than average mosquito activity. Braintree, Canton, Foxboro, Franklin, Holbrook, Medfield, Medway, Millis, Milton, Norfolk, and Wrentham reported higher than average numbers; whereas Walpole reported lower than average activity. Bellingham, Dedham, Needham, and Plainvillereported average mosquito activity.

Gravid Traps:
For the first time in many weeks, gravid mosquito activity has returned to more normal numbers. The towns of Canton, parts of Dedham, Franklin, Holbrook, parts of Quincy, and parts of Sharon experienced higher than average gravid mosquito activity. Parts of Dedham, Medfield, Needham,Norwood, and Randolph continued with the lower than average mosquito count trend. The remaining towns now report average gravid mosquito activity.

2. Current Predominant Species

CDC Light Traps:
The most predominant CDC trapped mosquitoes in Norfolk County this week were Culex pipiens/restuans and Aedes vexans. Culiseta melanura has been highly active and numerous in the towns of Avon and Holbrook. Ochlerotatus canadensis populations are high in Avon, Foxboro, and Sharon. Although their numbers are slowly declining, Coquillettidia perturbans populations are high in Avon, Braintree, Millis, and Norfolk. Newly emergedOchlerotatus triseriatus have made their presence felt in Medfield, resulting in higher than average activity for the town. Ochlerotatus trivittatus have also made a prominent presence in Canton and Norfolk. Psorophora ferox populations continue to be higher than average in Canton. The Charles and Neponset River flood plains have dried down to near normal conditions. The USGS stream flow monitoring stations on both rivers are indicating a flow at the 75th to 89th percentile which means these river system remain prone to flooding. Even with the drier weather, site visits continue to show high levels of human biting mosquito activity although there has been a “slight” decline in rates from Epi Week 32.

Gravid Traps:
Although gravid traps remain predominated by Culex pipiens/restuans, there was an odd occurrence of higher than average Anopheles punctipennis andUranotaenia sapphirina populations in parts of Dedham. Ochlerotatus japonicus numbers have returned to average in most towns.

3. Comparison to previous season

Host-seeking mosquito activity this week was mixed, with higher than average numbers attributed to Culex pipiens/restuans populations. Coquillettidia perturbans and Aedes vexans were higher than average in some parts of the county, but it appears that their numbers are slowly declining when compared with previous weeks. There were localized population booms of Ochlerotatus triseriatus and Ochlerotatus trivittatus in some parts of the county. Consistent with previous weeks’ activity, Psorophora ferox numbers continue to be high in Canton. Gravid trap activity has returned to normal in most parts of Norfolk County. Some towns reported higher than average gravid mosquito activity whereas a few towns continued with the lower than average count trend. There was an oddly high population of Anopheles punctipennis and Uranotaenia sapphirina in parts of Dedham.

4. Weather Summary

This week was hot and very humid with two episodes of rainfall. A cluster of thunderstorms moved across the county along and to the west of I – 95 on Thursday providing ¼ to ¾ of an inch of rain across these areas with little if any rainfall east of I-95. The second batch of rainfall was Saturday night into pre-dawn hours of Sunday associated with the fringes of Hurricane Bill. This provided another widespread ¼ to ¾ of an inch of rain. Despite this, our monthly rainfall remains below normal (25% to 75% of normal) countywide.

Total weekly rainfall: 1.34 inches (+0.46 in.)
Total Monthly rainfall: 1.78 inches (-0.69 in.)
Total Yearly rainfall: 28.59 inches (+1.79 in.)

5. Number of requests for service

NCMCP received 5,016 calls for service as of 8/22/09. NCMCP received 439 calls for service this week.

6. MCP/Commission response

NCMCP continues to conduct “area wide” ground ULV applications in many areas of the county due to high numbers of calls as a result of these large populations of human biting mosquitoes. Calls for service declined slightly from last week to this week but are still running high. Due to this continuing high demand ULV activities have been expanded again this week especially in towns adjacent to the Charles and Neponset River flood plains. NCMCP is wrapping up treatments to rain basins in high density basin areas such as centers of towns. It appears with the less frequent flushing of Culexhabitat that their numbers are recovering to more normal levels. Coordination between NCMCP and all local Boards of Health is ongoing relative to interpretation of surveillance data and how best to get the word out to the public relative to avoidance of mosquito bites. NCMCP remains prepared to conduct additional ground adulticide, ground larvicide and aerial larvicidecontrol activities as required.


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