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

SurveillanceAn. freeborni, the western malaria mosquito, is a large mosquito and ismost active at dusk and will readily enter houses. It can be a significantnuisance during its peak population periods. Females feed on mostmammals and are most active in the dusk and early evening hours. Thisspecies may be abundant in rice fields, and occurs in clear, seepage waterin sunlit algae-laden pools. It usually has a bi-modal population trendwith the first peak in February and a second, greater peak in Augustand September, when it can be considered a major pest due to the bitingactivity. In 2011 An. freeborni populations were much higher early inthe season than in previous years, as expected by the higher populationsobserved later in the season in 2010 going into the winter. Later in the year,numbers followed the same trend as previous years, with a peak in August,although this second peak seemed wider than the 5 year average for thisspecies. Other Anopheles species found in our area are An. franciscanusand An. punctipennis.ABUNDANCE TRENDS OF MOSQUITO VECTORSOF DISEASE IN SACRAMENTO AND YOLOCOUNTIES IN 2011No. females per trap night3632282420161284Culex pipiens 2006–2011There are several Aedes species of mosquitoes which are also of concernto the District. Ae. melanimon and Ae. nigromaculis are floodwatermosquitoes. They lay eggs on ground which will become flooded later,either by natural flooding or by agricultural practices. When the fieldswith eggs on them are flooded, the larvae emerge from the eggs anddevelop to the adult stage. When this occurs the resulting biting activityfor humans and other mammals in the area is significant. For this reason,these mosquitoes are not primarily of disease transmission concern but ofnuisance concern. These mosquitoes are day and dusk biting mosquitoesrather than the principally dusk biting type of the Culex and Anophelesspecies. Another Aedes mosquito of interest is Ae. sierrensis, the westerntreehole mosquito. This mosquito is the primary vector of canine heartwormin our area. It is unique in that its natural breeding source is treeholes. Thisspecies is difficult to control as there can be numerous trees with treeholesin a wooded area and the treeholes can be at varying heights, and thusdifficult to treat with mosquito control products, even though it has a limitedflight range. This is a small black and white mosquito and it is active duringthe day as well as at dusk. All of these Aedes mosquitoes are primarilymammal biting mosquitoes. Other less common Aedes sp. that can befound in our area and can be a localized nuisance or concern include: Ae.washinoi, Ae. vexans, Ae. sticticus, and Ae. bicristatus. Another mosquitospecies that can be found in treeholes and sometimes artificial woodencontainers in our District’s area is Orthopodomyia signifera, but it is not ascommon as Ae. sierrensis.In addition to the species mentioned above, which are all active primarilyduring the spring and summer months, the Culiseta sp. mosquitoes areactive either primarily in the winter months (Cs. inornata) or all year long(Cs. incidens). These are large mosquitoes and are primarily mammalbiters which feed usually at dawn and dusk. Cs. inornata and Cs. incidensbreed in a variety of natural aquatic habitats, with Cs. incidens also beingadapted to artificial containers and more polluted sources as well. Thesemosquitoes are primarily nuisance mosquitoes; however Cs. incidens hasbeen suggested as a canine heartworm vector and is a secondary vectorof West Nile virus. Cs. particeps is also found in our District area, but is notas common in our traps as Cs. inornata and Cs. incidens.No. females per trap nightNo. females per trap night036322824201612840363228242016128405 year average 2011Anopheles freeborni 2006–20115 year average 2011Culex tarsalis 2006–20115 year average 2011In addition to adult mosquito surveillance, the District conducts an intensive immature mosquito surveillance program. Mosquito breeding sourcesare routinely inspected by field technicians, who collect mosquito larvae and bring them to the District’s laboratory for identification. The dataprovided by the program is used for targeting control efforts and determining their efficacy.2011 Annual Report9