Ask Axios: Does mosquito spray kill good bugs?

"Does anyone know if this (mosquito) spray also kills larvae of beneficial insects?" — Kathleen Elsberry, DSM

Driving the news: Helicopter applications of the larvicide spinosad were applied last week in areas of unincorporated Polk County that hold water and are prime mosquito habitat.

• And Des Moines launched the season's first city-wide mosquito treatment yesterday via trucks.

Answer: When applied appropriately, the risk to non-target species is mitigated, Dave Williamson, a code enforcement manager for Polk County, tells Axios.

Zoom in: Spinosad is highly toxic to bees but the threat is greatly reduced if it's applied in the evening when they are not active, according to a 2019 paper from Michigan State University.

Yes, but: It also suppresses a broad number of caterpillar species and shouldn't be used in areas where threatened or endangered butterflies are located.

Polk and DSM officials use granular or tablet forms of mosquito pesticides, which are applied directly to standing water and pose little or no threat to bees, spokespeople said.

• DSM additionally uses spray applications in neighborhoods, which are applied at dusk or dawn as recommended.

The big picture: Diseases like the West Nile virus and malaria can be spread to humans by mosquito bites, according to the CDC.

⛔️ Opt out: DSM residents can request no spray of their property online or by calling 800-942-2555.

Editors note: This story first appeared as an "Ask Axios" question in the Axios Des Moines newsletter.