2011 Annual Report - Sacramento-Yolo Mosquito & Vector Control ...

Surveillance6.5%9.2%.9%13.1%American Light TrapsIn 2011 the District used 26 American Lighttraps in fixed sites within Sacramento andYolo Counties for a total of 1,314 trappingnights. The total number of mosquitoescollected with those traps was 56,465. Ofthese, 36,579 (64.8%) were females. Themost abundant mosquito species capturedby the American Light traps were Culextarsalis, followed by Culex pipiens, Culisetainornata, Aedes melanimon, Anophelesfreeborni, Culiseta incidens, and Culexerythrothorax. Other mosquito species werecollected in smaller numbers and accountedfor less than 2% of the total collection.American Light Trap Collection2.0% 1.8%9.9%9.2%6.5%24.5%13.1%Magnet Traps ®The District used a total of 26 MosquitoMagnet traps in 2011 in Sacramentoand Yolo Counties during 1,173 trappingnights. A total of 74,810 mosquitoes werecollected by these traps, and most (94%)were females. The most abundant speciescollected were Cx. tarsalis, An. freeborni,Ae. melanimon, Aedes washinoi, Cs.inornata, Cx. pipiens, Cx. erythrothorax,and Cs. incidens. Other species collectedaccounted for less than 1% of the totalcollection.Mosquito Magnet Trap CollectionMosquito Magnet Trap CollectionMosquito Magnet Trap CollectionAmerican Light Trap Collection4.8% 2.8% 1.5% 0.9%5.2%2.0% 1.8%4.8% 2.8% 1.5% 0.9%Cx 5.3% tarsalis5.2%33.0%Cx pipiensCs inornata33.0%Cx tarsalis 5.3%Ae melanimonCx pipiensAn freeborni 9.5%Cs inornata51.4%Cs incidensAe melanimonCx erythrothoraxAn freeborni 9.5%Other18.7% Cs incidensCx erythrothorax24.5%Other18.7%American Light Trap Collection51.4%5.2%6.3%Cx tarsalisAn freeborniAe melanimonAe washinoiCs inornataCx pipiensCx erythrothoraxCs incidensOther3.1% 0.9%Gravid TrapsA total of 26 Gravid traps were used in2011 in Sacramento and Yolo Countiesduring 1,321 trapping nights. A total of37,880 mosquitoes were collected by thesetraps, and most (88.3%) were females. Themost abundant species, as expected, wasCx. pipiens, followed by Cs. incidens, An.freeborni, and Cx. tarsalis. Other mosquitospecies constituted less than 1% of the totalcollection.Gravid Trap CollectionGravid Trap CollectionGravid Light Trap Collection5.2%Cx tarsalis6.3%An freeborniAe melanimonAe washinoi84.5%Cs inornataCx pipiensCx erythrothoraxCs incidensOther3.1% 0.9%84.5%Cx pipiensCs incidensAn freeborniCx tarsalisOtherCx pCs iAn fCx tOthAdult mosquito abundance trendsAll mosquito species are monitored throughout the year, but theDistrict is particularly interested in the abundance of certain speciesfrom the standpoint of disease transmission and nuisance. Two Culexspecies, Cx. pipiens and Cx. tarsalis, are considered the main vectorsof West Nile virus in our area. The abundance of these species isclosely monitored and is used as part of the risk assessment for WestNile virus transmission. Cx. pipiens, the northern house mosquito, isa medium-sized, brown mosquito, which usually breeds in foul orpolluted waters, such as artificial containers, fish ponds, improperlymaintained swimming pools, catch basins, septic tanks, dairy drains,waste treatment ponds, etc. It tends to bite in the dusk or early eveninghours of the day and feeds mostly on birds, but will readily bitemammals, including humans. In 2011, abundance for this speciesfollowed the same pattern as observed in previous years, with twopeaks – a major peak in June and another in September. Comparedto the 5 year average, Cx. pipiens numbers were much higher at thefirst peak in June, and the peak was about one to two weeks later thanthe average.Cx. tarsalis, the western encephalitis mosquito, is also a medium-sizedand brownish mosquito, with a median white band on the proboscisand white bands on the legs. This species can colonize a widevariety of aquatic sources, such as wetlands, duck clubs, rice fields,and irrigated crops, but in recent years it has been commonly foundin significant numbers also in suburban and urban environments,breeding in abandoned or not maintained swimming pools. It is also abird feeding mosquito that may feed readily on humans, and it is mostactive in the dusk and early hours of the evening. In 2011, there wasa major peak in Cx. tarsalis numbers in August, four weeks later thanthe 5 year average peak for that species.Cx. erythrothorax is a distinctive orange to light brown mosquito whichinhabits tule pond areas. It does not fly long distances and usuallystays near the location of its breeding source. Another Culex sp., Cx.stigmatosoma is a foul water breeding mosquito and has banded legslike the Cx. tarsalis mosquito. These mosquitoes can vector West Nilevirus, but are not particularly widespread. We also find Cx. thriambusand Cx. apicalis in our District’s area.8 Sacramento–Yolo Mosquito & Vector Control District