Week 29 – July 15 – 16

2009 Mosquito Report: Week 29

Report based on data collected from traps deployed on Wednesday, July 15, 2009 and retrieved on Thursday, July 16, 2009. Report prepared by John Smith, Chan Suom, M.S., and Nate Boonisar.

1. Current mosquito activity/trend

CDC Light Traps:
As predicted, most towns across Norfolk County experienced a significantly higher than average host-seeking mosquito activity, due in large part toAedes vexans. Franklin and Plainville host-seeking mosquito activity was average, whereas Medfield, Needham, and Norfolk encountered lower than average activity.

Gravid Traps:
Gravid mosquito activity varied across Norfolk County. The following towns recorded higher than average mosquito samples: Avon, Bellingham,Canton, Franklin, Medfield, Medway, Milton, Norfolk, parts of Quincy, parts of Sharon, Stoughton, and Weymouth. Braintree, Dover, Dedham, Foxboro, Millis, Westwood, and Wrentham reported average activity, whereas Holbrook, Needham, Norwood, Plainville, Randolph, and Walpoleexperienced lower than average gravid mosquito activity.

2. Current Predominant Species

CDC Light Traps:
The most predominant CDC trapped mosquitoes this week were Aedes vexans and Coquillettidia perturbans. Notably, high Psorophora feroxpopulations have appeared especially in Canton. There are isolated spikes in Oc. canadensis and Oc. excrucians populations across the county. Oc.trivittatus has made a significant appearance in Canton and Walpole. The Weymouth trap collected a higher than usual population of Ae. cinereus. Oddly enough, Culex pipiens/restuans populations remain high in Foxboro, Holbrook, Medway, Millis, and Quincy in our CDC traps. Field site visits of theNeponset River floodplain is showing a rapid drying down to more normal river flow conditions. Cs. melanura numbers are above the average at the Holbrook site which has collected positive EEE pools in the past. If incidence of EEE in Cs. melanura collections continues and/or increases we will need to keep an eye on the aging populations of the mammal biting species such as Aedes vexans, Oc. canadensis and Coquillettidia perturbans. NCMCP may consider submission of more of these species for virus analysis if this occurs.

Gravid Traps:
Gravid traps collections are predominately Culex pipiens/restuans. Most collections are at or above their averages for this week. Avon and Miltoncollected higher than average Oc. japonicus populations, the remainder of Norfolk County reported lower than average numbers of Oc. japonicus.

3. Comparison to previous season

Host-seeking mosquito activity this week was higher than average due to the recent emergence of Ae. vexans as a result of previous, numerous rain events creating suitable habitat all around the county although this is most pronounced in communities associated with the Neponset River due to recent flooding of this river system. Coquillettidia perturbans populations remain high in many parts of Norfolk County. Ps. ferox and Oc. trivittatus havemade their first significant debut in our CDC traps in Canton and Walpole. Isolated populations of Culex pipiens/restuans remain strong in some parts of the county. Gravid trap activity for Norfolk County was varied and may be a result of scattered rain events disturbing and/or flooding larval habitat of this species. It is important to note that this trap period had ideal weather conditions, the first time this season. The higher numbers collected this week compared to previous weeks may be due to this favorable weather and not entirely as a result of population increases. Having noted this, we do believe that population increases are occurring in certain reflood species. Comparisons between numbers collected in 2009 and the average for each trap may be more informative than comparisons of trends from last week to this week.

4. Weather Summary

This week featured drier weather with rain showers and thunderstorms at both ends of the week. Predawn showers on Sunday the 12th produced a general 0.5 – 0.75 inches of rain county-wide. Another round of showers and thunderstorms on the night of the 17th-18th produced a widespread 0.25-0.75 inches of rain. Totals for the week were between 0.75 and 1.25 inches across the region which is near to slightly above normal.

Total weekly rainfall: 0.94 inches (+0.26 in.)
Total Monthly rainfall: 3.46 inches (+1.68 in.)
Total Yearly rainfall: 23.24 inches (+0.19 in.)

5. Number of requests for service

NCMCP received 2,243 calls for service as of 7/17/09. NCMCP received 387 calls for service this week.

6. MCP/Commission response

NCMCP has been conducting “area wide” ground ULV applications in areas of high calls or where light trap/landing count collections dictate additional applications. Due to an increase in demand these ULV activities have been expanded this week. NCMCP continues treatments to rain basins in high density basin areas such as centers of towns although these activities have been interrupted from time to time due to redeployment of field staff to other ground larvicide activities. Coordination between NCMCP and the 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, groundlarvicide and aerial larvicide control activities as required.


144 Production Rd, Suite C

Walpole, MA 02081

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Fax: (781) 769-6436