Week 34 – Aug 20 – 21

2008 Mosquito Report: Week 34

Report based on data collected from traps deployed on Wednesday, August 20, 2008 and retrieved on Thursday, August 21, 2008. Report prepared by John Smith, Chan Suom, M.S., and Nate Boonisar.

1. Current mosquito activity/trend

CDC Light Traps:
CDC activity, once again, reflected a mix of reflood/floodwater species including Aedes vexans, Psorophora ferox and Ochlerotatus canadensis. Compared to Week 34 in 2007, the towns of Avon, Canton, Dedham, Franklin, Holbrook, Millis, Milton, Needham, Norfolk, and Plainville experienced higher CDC trap activity due in large part to the emergence of Aedes vexans from recent rain/flood events, though trap counts remain relatively low compared to last week’s figures. Aedes vexans numbers, in general, continued falling off their peak of week 32. Ochlerotatus canadensis numbers seem to indicate lower level activity across the county. Salt marsh mosquito activity continues along the coast in fairly high numbers.

Gravid Traps:
Gravid trap activity showed increased activity in the towns of Avon, Bellingham, Braintree, Canton, Dedham, Franklin, Holbrook, Millis, Milton, Needham, Norfolk, Norwood, Quincy, Randolph, Sharon, Stoughton, Walpole, Westwood, and Weymouth. Gravid trap collections, in many areas, increased dramatically from week 33 to week 34 with many trap sites at or above their multi year average. Recent heavy rain events no doubt had an impact on Culex spp.s production. Ochlerotatus japonicus populations are increasing at some of the traps sites while declining at others.

2. Current Predominant Species

The most predominant mosquito in CDC traps this week was again Aedes vexans. Culex spp.s were the second most common species in most CDC traps, followed by Coquillettidia perturbans and Ochlerotatus canadensis. Culiseta melanura collections remain very low relative to their multi year averages.

3. Comparison to previous season

CDC collections continue to show an active period for reflood/floodwater species. The trend in collections of Aedes vexans numbers over the past couple of weeks indicates a fairly rapid decline. Ochlerotatus canadensis numbers are low but do indicate some activity in many parts of the county. The bad news is that many of the gravid trap collections showed significant increases especially in the eastern most traps. In general, we are seeing more activity later this season when compared to the end of the 2007 season.

4. Weather Summary

A pattern change this week brought mainly dry weather to the county. A cold frontal passage on Tuesday brought a brief period of showers to most of the county, with some heavier thunderstorms in eastern sections. Rainfall amounts ranged from a trace to 0.10” across most of the county, with some local amounts up to ¼ inch across far eastern sections. The cold front brought sunny, dry, but cool weather for the remainder of the week with temperatures averaging slightly below normal.

Total weekly rainfall: 0.04 inches (+0.73 in.)
Total Monthly rainfall: 4.93 inches (+2.46 in.)
Total Yearly rainfall: 33.02 inches (+6.22 in.)

5. Number of requests for service

Year to date NCMCP has received 3,781 calls for service as of 8/23/08. This represents a total of 329 calls for the week. Numbers of calls per week are approach the higher weekly call numbers of the past two seasons again most likely due to higher numbers of reflood/floodwater species present at this time. Last year at this time the calls for service (year to date) were 5,184.

6. MCP/Commission response

In general our response has been to continue ground ULV applications targeting areas of high public demand and areas of positive WNv mosquito pools.Additional trapping of gravid Culex pipiens/restuans has taken place in areas active for WNv. Coordination between NCMCP and the local Boards of Health is ongoing relative to control/surveillance options in the vicinity of WNv positive birds/mosquito pools.


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