CORVALLIS, Ore. — The increased number of mosquitoes flying around Western Oregon this summer could lead to an unintended consequence: a spike in non-native fish released into home water features, ponds and wetlands in attempts to control the insect.
These do-it-yourself solutions are not effective for mosquito control and they harm the environment.
That’s according to Sam Chan, Oregon State University Sea Grant Extension watershed health and aquatic invasive species specialist, and Dana Sanchez, Extension wildlife specialist. Two of the most common fish released are the guppy (Poecilia reticulata) and the western mosquitofish (Gambusia affinis), because they eat mosquito larvae.
These do-it-yourself solutions are not effective for mosquito control and they harm the environment, Chan and Sanchez said. It's against the law in Oregon to release non-native fish into any public waterway, and a permit is required for private land. Even releases into small backyard ponds and water features can become problematic if a flood allows fish to escape.
"Those wanting to or who have made these releases may not know that there are more effective long-term solutions or realize that Gambusia will consume much more than mosquito larvae, including native fish, amphibians, invertebrate insects and zooplankton," Chan said. "In Western Oregon, many of the native fish, amphibians and aquatic invertebrates such as dragonflies also consume mosquito larvae."
Chan is also concerned that released mosquitofish and guppies consume zooplankton, which feed on algae. Without zooplankton, harmful algal blooms can form. Oregon has seen several in recent years.
Frogs missing after cold spring
This year’s large mosquito hatch was likely the result of a wet spring. Sub-freezing temperatures in April destroyed frog egg masses, Sanchez said, leaving many residents without their best mosquito-eating allies.
"Field sampling this year has revealed that quite a few previously active and even abundant frog sites had low to no reproduction this year," she said.
Steps to reduce mosquito habitat
The first step to controlling mosquito populations is habitat management, Sanchez said. According to the Oregon Department of Fish and Wildlife, recommended actions include:
- Minimize standing water around homes, structures and irrigated areas
- Eliminate water-filled containers such as buckets and old tires
- Clean roof gutters and connect and drain roof drains properly
- Manage water troughs and birdbaths
Safer alternatives to fish releases
A targeted biological control for mosquito larvae is Bacillus thuringiensis israelensis (Bti), Sanchez said. This naturally occurring bacterium, widely sold in affordable “mosquito dunks,” is safe around mammals, birds, fish and amphibians.
Acoustic sonic devices are also an effective tool, Chan said. Placed in water where mosquito larvae live, the devices emit specific wavelengths that disrupt larvae development.
Using Bti or sonic devices, along with preventive habitat management, are more effective and sustainable ways to reduce mosquito populations than releasing non-native fish, Sanchez said.
Sanchez, an associate professor, and Chan, an assistant professor, are faculty members in Oregon State’s Department of Fisheries, Wildlife, and Conservation Sciences in the College of Agricultural Sciences.
Previously titled Releasing non-native fish to control mosquitoes is often ineffective and harmful to environment
