It’s monsoon season and that means more mosquitoes in the air. Regional Flood Control District (RFCD) staff use several methods to reduce the numbers of all types of mosquitoes.
The District is responsible for maintenance of 62 detention basins in the unincorporated areas of Pima County. Two older regional stormwater detention basins, Camino Verde Basin on Camino Verde Road south of Ajo Way and the Massingale Basin on Massingale Road and Camino de Oeste, are slow to drain naturally. When these basins receive significant amounts of drainage, RFCD first uses heavy-duty pumps to reduce the amount of standing water. Then the remaining water is treated with a granular larvicide called BTI. BT stands for Bacillis thuringensis, a group of natural soil-dwelling bacteria; the I stands for israelensis, the specific strain of the bacteria that kills mosquitoes in the larval stage. It is safe for birds and all other animals. In fact, BTI is available in floating “dunks” for home use at local hardware stores. Smaller basins are also treated with BTI as required if water remains in them for more than several days.
Most mosquito bites are irritating, but harmless. “Floodwater mosquitoes (so-called ankle biters) are not typically mosquito species that are disease vectors and they don’t carry West Nile virus,” explains Chris Cawein, Deputy Director at RFCD. “Whenever rain hits, we look at the storm report and gauges” to determine which large and small basins or areas might need treatment. “Most basins drain within one to two days, but if they retain water for more than three days, they’re on the list to treat.”
“We do a lot of preparatory work before the monsoon season to improve drainage in certain problematic basins and other areas to reduce mosquito breeding habitat,” says Cawein. Regardless of the preparatory work, some areas just will drain slowly.
He says mosquito abatement activities can run anywhere from April to October, but “our season is driven by rain events, with July through September being the primary months. After the first frost – typically in October, mosquitoes aren’t too much of a problem.”
Pima County Health Department monitors mosquitoes in four areas and provides counts to RFCD from traps at Cortaro Mesquite Bosque, Mesquite Circle Pond, Arroyo Chico Phase 2, and Rillito River/Swan Wetlands. RFCD uses this data to determine which areas need treatment.
Some areas are treated weekly, like the Kino Environmental Restoration Project area on Ajo Way across from Kino Veterans’ Memorial Stadium, “because people use the trails there, it’s near other parks, and there’s a large body of water,” says Cawein. “The larvicide lasts a week and keeps the mosquito population under control.”
Contact RFCD at 243-1800 to report mosquito activity, and standing water in basins, washes or on District property.